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  • 1.
    Alvi, Muhammad Rouf
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Burkhard O., Jahn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Computational Investigation of Brook-Type Silabenzenes and Their Possible Formation through [1,3]-Si -> O Silyl Shifts2013In: Organometallics, ISSN 0276-7333, E-ISSN 1520-6041, Vol. 32, no 1, p. 16-28Article in journal (Refereed)
    Abstract [en]

    Quantum chemical calculations with the M062X hybrid meta density functional theory method were performed in order to examine formation of Brook-type silabenzenes 4a 4l, silapyridines 6a 6d, and five-membered ring silaheteroaromatics 8a8d through [1,3]-trimethylsilyl (TMS) and [1,3]-tri(isopropyl)silyl (TIPS) shifts from a tetrahedral silicon atom to an adjacent carbonyl oxygen of cyclic conjugated acylsilane precursors. All Brook-type silabenzenes and silapyridines, having a 2-trialkylsiloxy substituent, are at lower relative energies than their precursors, whereas silaheteroaromatics 8a 8d are found at slightly higher energies. The free energies of activation for the thermal [1,3]-TMS shifts range from 29 to 44 kcal/mol, with the lowest for a Brook-type silapyridine and the highest for a silafuran. The geometries of the Brook-type silabenzenes, silapyridines, silafuran and silathiophene indicate aromatic character, but the silapyrroles are nonaromatic. At M062X/6-311+G(d)//M062X/6-31G(d) level all Brook-type silabenzene dimers studied herein are more stable than two silabenzenes, also for a silabenzene with bulky TIPS, OTIPS and tert-butyl substituents (4l). Yet, comparisons of the B3LYP/6-31G(d) dimerization energies of 4l with that of the isolable 1-Tbt-silabenzene (Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl) of Tokitoh [J. Chin. Chem. Soc. 2008, 55, 487] indicate that 4l will also be a monomeric silabenzene, and thus, a suitable synthetic target.

  • 2.
    Ayub, Rabia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    El Bakouri, Ouissam
    Univ Girona, IQCC, C Maria Aurelia Capmany 6, Girona 17003, Catalonia, Spain..
    Jorner, Kjell
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Sola, Miguel
    Univ Girona, IQCC, C Maria Aurelia Capmany 6, Girona 17003, Catalonia, Spain..
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Can Baird's and Clar's Rules Combined Explain Triplet State Energies of Polycyclic Conjugated Hydrocarbons with Fused 4n pi- and (4n+2)pi-Rings?2017In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 82, no 12, p. 6327-6340Article in journal (Refereed)
    Abstract [en]

    Compounds that can be labeled as "aromatic chameleons" are pi-conjugated compounds that are able to adjust their pi-electron distributions so as to comply with the different rules of aromaticity in different electronic states. We used quantum chemical calculations to explore how the fusion of benzene rings onto aromatic chameleonic units represented by biphenylene, dibenbzocyclooctatetraene, and dibenzo[a,e]pentalene modifies the first triplet excited states (T-1) of the compounds. Decreases in T-1 energies are observed when going from isomers with linear connectivity of the fused benzene rings to those with cis- or transbent connectivities. The T-1 energies decreased down to those of the parent (isolated) 4n pi-electron units. Simultaneously, we observe an increased influence of triplet State aromaticity of the central 4n ring as given by Baird's rule and evidenced by geometric, magnetic, and electron density based aromaticity indices (HOMA, NICS-XY, ACID, and FLU). Because of an influence of,triplet state aromaticity in the central 4n pi-electron units,, the most stabilized, compounds, retain the triplet excitation in Baird pi-quartets or octets, enabling the outer benzene rings to adapt closed-shell singlet Clar pi-sextet character. Interestingly, the T-1 energies go down as the total number of aromatic cycles within a molecule in the T-1 state increases.

  • 3.
    Ayub, Rabia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Jorner, Kjell
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    The Silacyclobutene Ring: An Indicator of Triplet State Baird-Aromaticity2017In: Inorganics, ISSN 2304-6740, Vol. 5, no 4, article id 91Article in journal (Refereed)
    Abstract [en]

    Baird's rule tells that the electron counts for aromaticity and antiaromaticity in the first pi pi* triplet and singlet excited states (T-1 and S-1) are opposite to those in the ground state (S-0). Our hypothesis is that a silacyclobutene (SCB) ring fused with a [4n]annulene will remain closed in the T-1 state so as to retain T-1 aromaticity of the annulene while it will ring-open when fused to a [4n + 2]annulene in order to alleviate T-1 antiaromaticity. This feature should allow the SCB ring to function as an indicator for triplet state aromaticity. Quantum chemical calculations of energy and (anti)aromaticity changes along the reaction paths in the T-1 state support our hypothesis. The SCB ring should indicate T-1 aromaticity of [4n]annulenes by being photoinert except when fused to cyclobutadiene, where it ring-opens due to ring-strain relief.

  • 4.
    Ayub, Rabia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Papadakis, Raffaello
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Jorner, Kjell
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics. uppsala university.
    Zietz, Burkhard
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics. uppsala university.
    Cyclopropyl Group: An Excited-State Aromaticity Indicator?2017In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 23, no 55, p. 13684-13695Article in journal (Refereed)
    Abstract [en]

    The cyclopropyl (cPr) group, which is a well-known probe for detecting radical character at atoms to which it is connected, is tested as an indicator for aromaticity in the first * triplet and singlet excited states (T-1 and S-1). Baird's rule says that the -electron counts for aromaticity and antiaromaticity in the T-1 and S-1 states are opposite to Huckel's rule in the ground state (S-0). Our hypothesis is that the cPr group, as a result of Baird's rule, will remain closed when attached to an excited-state aromatic ring, enabling it to be used as an indicator to distinguish excited-state aromatic rings from excited-state antiaromatic and nonaromatic rings. Quantum chemical calculations and photoreactivity experiments support our hypothesis; calculated aromaticity indices reveal that openings of cPr substituents on [4n]annulenes ruin the excited-state aromaticity in energetically unfavorable processes. Yet, polycyclic compounds influenced by excited-state aromaticity (e.g., biphenylene), as well as 4n-electron heterocycles with two or more heteroatoms represent limitations.

  • 5.
    Chajara, Khalil
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry. Department of Biochemistry and Organic Chemistry, Organic Chemistry II. Organisk kemi.
    Ottosson, Henrik
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry. Department of Biochemistry and Organic Chemistry, Organic Chemistry II. Organisk kemi.
    An improved pathway to 6,6-disubstituted fulvenes2004In: Tetrahedron Letters, no 45, p. 6741-6744Article in journal (Refereed)
    Abstract [en]

    Pentafulvenes with alkyl and/or aryl substituents at the exocyclic position are formed rapidly in high yields through reaction of crystalline sodium cyclopentadienide directly with the appropriate ketones.

  • 6. Czyzewski, Michal
    et al.
    Bower, Justin
    Box, Matthew
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Steel, Patrick G.
    Silene equivalents through the rhodium-catalysed reactions of alpha-hypersilyl diazoesters: a computational and experimental study2011In: Chemical Science, ISSN 2041-6520, Vol. 2, no 12, p. 2367-2372Article in journal (Refereed)
    Abstract [en]

    The generation of silenes through the rhodium-catalysed decomposition of alpha-hypersilyl diazocarbonyl compounds has been explored both computationally and experimentally. This transformation proceeds via a pathway involving initial formation of the carbene, followed by rearrangement, initially to a silene and ultimately to a ketene. Density functional theory (DFT) calculations of model compounds suggested that silene formation was most preferential with electron donating substituents attached to the carbonyl group. The predictions were experimentally evaluated and hypersilyl diazoacetates provided an unusually long-lived species (t(1/2) > 40 h) that reacts as a formal silene equivalent. Further DFT calculations support the formation of an internally stabilised silene in the form of a 1,2-silaoxetene. Importantly the acylsilene-silaoxetene reaction is reversible and consequently this silene equivalent reacts with alpha,beta-unsaturated carbonyl compounds to form cyclic silyl enol ethers which have considerable potential for further synthetic transformations.

  • 7. Czyzewski, Michal
    et al.
    Sellars, Jonathan D.
    Guliashvili, Tamaz
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Tibbelin, Julius
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Johnstone, Lisa
    Bower, Justin
    Box, Matthew
    Davies, Robert D. M.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Steel, Patrick G.
    The first intramolecular silene Diels-Alder reactions2014In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 50, no 22, p. 2919-2921Article in journal (Refereed)
    Abstract [en]

    The synthesis of silaheterocycles through the first examples of an intramolecular silene Diels-Alder reaction is described.

  • 8.
    Dahlstrand, Christian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Jahn, Burkhard O.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Villaume, Sebastien
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Polyfulvenes: Polymers with "Handles" That Enable Extensive Electronic Structure Tuning2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 46, p. 25726-25737Article in journal (Refereed)
    Abstract [en]

    The fundamental electronic structure properties of substituted poly(penta)fulvenes and pentafulvene-based polymers are analyzed through qualitative molecular orbital (MO) theory combined with calculations at the B3LYP and HSE06 hybrid density functional theory (DFT) levels. We argue that the pentafulvene monomer unit has a unique character because electron density in the exocyclic C=C double bond can be polarized into and out of the five-membered ring, a feature that is not available to other more commonly used monomers. It is investigated how the energy gaps between the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO, respectively), as approximate band gaps, are influenced by exocyclic substitution, introduction of linker groups, benzannulation, and ring substitution. In particular, the exocyclic positions of the fulvene act as handles by which the electronic structure of the polymer can be tuned between the quinoid and fulvenoid valence bond isomers; electron-withdrawing exocyclic substituents lead to polyfulvenes in the quinoid form while those with electron-donating substituents prefer the fulvenoid. Taken together, the HOMO-LUMO gaps of polyfulvenes can be tuned extensively, varying in ranges 0.77-2.44 eV (B3LYP) and 0.35-2.00 eV (HSE06) suggesting that they are a class of polymers with highly interesting, yet nearly unexplored, properties.

  • 9.
    Dahlstrand, Christian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Rosenberg, Martin
    Department of Chemistry, University of Copenhagen.
    Kilså, Kristine
    Department of Chemistry, University of Copenhagen.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Exploration of the π-Electronic Structure of Singlet, Triplet, and Quintet States of Fulvenes and Fulvalenes Using the Electron Localization Function2012In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 116, no 20, p. 5008-5017Article in journal (Refereed)
    Abstract [en]

    The singlet ground states and lowest triplet states of penta- and heptafulvene, their benzannulated derivatives, as well as the lowest quintet states of pentaheptafulvalenes, either the parent compound or compounds in which the two rings are intercepted by either an alkynyl or a phenyl segment, were investigated at the (U)OLYP/6-311G(d,p) density functional theory level. The influence of (anti)-aromaticity was analyzed by the structure-based aromaticity index HOMA, the harmonic oscillator model of aromaticity. The extent of (anti)aromatic character was also evaluated in terms of the pi-electron (de)localization as measured by the pi component of the electron localization function (ELF pi). The natural atomic orbital (NAO) occupancies were calculated in order to evaluate the degree of pi-electron shift caused by the opposing electron-counting rules for aromaticity in the electronic ground state (S-0; Hiickel's rule) and the first pi pi* excited triplet state (T-1; Baird's rule). Pentaheptafulvalene (5) shows a shift of 0.5 pi electrons from the 5-ring to the 7-ring when going from the S-0 state to the lowest quintet state (Qu(1)). The pentaheptafulvalene 5 and [5.6.7]quinarene 7 were also investigated in their 90 degrees twisted conformations. From our study it is apparent that excitation localization in fulvalenes, but not in fulvenes, to a substantial degree is determined by aromaticity localization to triplet biradical 4n pi-electron cycles. Isolated benzene rings in these compounds tend to remain as closed-shell 6 pi-electron cycles.

  • 10.
    Dahlstrand, Christian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Yamazaki, Kaoru
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Kilså, Kristine
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Substituent Effects on the Electron Affinities and Ionization Energies of Tria-, Penta-, and Heptafulvenes: A Computational Investigation2010In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 75, no 23, p. 8060-8068Article in journal (Refereed)
    Abstract [en]

    The extent of substituent influence on the vertical electron affinities (EAs) and ionization energies (IEs) of 43 substituted tria-, penta-, and heptafulvenes was examined computationally at the OVGF/6-311G(d)//B3LYP/6-311G(d) level of theory and compared with those of tetracyanoquinodimethane (TCNQ) and tetrathiafulvalene (TTF) as representing strong electron-acceptor and -donor compounds, respectively. The substituents X at the exocyclic positions of the fulvenes were either NH2, H, or CN, while the substituents Y at the ring positions were H, CI, F, CN, or NH2. The variations of the EAs and lEs were rationalized by qualitative arguments based on frontier orbital symmetries for the different fulvene classes with either X or Y being constant. The minimum and maximum values found for the calculated EAs of the tria-, penta-, and heptafulvenes were 0.51-2.05, 0.24-3.63, and 0.53-3.14 eV, respectively, and for the IEs 5.27-9.96, 7.07-10.31, and 6.35-10.59 eV, respectively. Two of the investigated fulvenes outperform TCNQ (calcd EA = 2.63 eV) and one outperforms TTF (calcd IE = 6.25 eV) with regard to acceptor and donor abilities, respectively. We also evaluated the properties of bis(fulvene)s, i.e., compounds composed of a donor-type heptafulvene fused with an acceptor-type pentafulvene, and it was revealed that these bis(fulvene)s can be designed so that the IE and EA of the two separate fulvene segments are retained, potentially allowing for the design of compact donor-acceptor dyads.

  • 11.
    Denisova, Aleksandra
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Emanuelsson, Rikard
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Expanding the (Cross-)Hyperconjugation of 1,4-Disilacyclohexa-2,5-dienes to Larger Monomers and Oligomers: A Computational Investigation2016In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 6, no 43, p. 36961-36970Article in journal (Refereed)
    Abstract [en]

    We used density functional theory calculations to examine molecules that can be regarded as expanded 1,4-disilacyclohexa-2,5-dienes as well as oligomers based on these or 1,4-disilacyclohexa-2,5-diene with the aim to identify systems with extended (cross-)hyperconjugation. Among the three "expanded 1,4-disilacyclohexa-2,5-dienes" considered cyclobutadisilole is the most interesting as it has a higher thermodynamic stability than the isomeric 1,6-disilacyclodeca-2,3,4,7,8,9-hexaene and significantly lower first electronic excitation energy than 1,6-disilacyclodeca-2,4,7,9-tetraene. Cyclobutadisilole with trimethylsilyl substituents at Si shows particularly low excitations with the first strong transition at 3.46 eV (358 nm), i.e., similar to 1.1 eV lower than in 1,4-disilacyclohexa-2,5-diene. The monomers were connected into oligomers via their Si atoms using bis(dimethylsilanediyl) linkers, and some extended hyperconjugation was revealed. The first allowed UV/Vis excitation in the cyclobutadisilole-based tetramers is calculated at 2.57 eV (482 nm), although the lowering in excitation energies when going from monomer to tetramer is merely similar to 0.5 eV and hyperconjugation has modest impact on geometries. Yet, the tetra(cyclobutadisilole) has a significantly lower first allowed excitation when compared to a previously studied tetra(1,4-disilacyclohexadiene) with first excitation at 3.9 eV (318 nm).

  • 12.
    Denisova V, Aleksandra
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Tibbelin, Julius
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Emanuelsson, Rikard
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    A Computational Investigation of the Substituent Effects on Geometric, Electronic, and Optical Properties of Siloles and 1,4-Disilacyclohexa-2,5-dienes2017In: Molecules, ISSN 1420-3049, E-ISSN 1420-3049, Vol. 22, no 3, article id 370Article in journal (Refereed)
    Abstract [en]

    Thirty two differently substituted siloles 1a–1p and 1,4-disilacyclohexa-2,5-dienes 2a–2p were investigated by quantum chemical calculations using the PBE0 hybrid density functional theory (DFT) method. The substituents included σ-electron donating and withdrawing, as well as π-electron donating and withdrawing groups, and their effects when placed at the Si atom(s) or at the C atoms were examined. Focus was placed on geometries, frontier orbital energies and the energies of the first allowed electronic excitations. We analyzed the variation in energies between the orbitals which correspond to HOMO and LUMO for the two parent species, here represented as ΔεHL, motivated by the fact that the first allowed transitions involve excitation between these orbitals. Even though ΔεHL and the excitation energies are lower for siloles than for 1,4-disilacyclohexa-2,5-dienes the latter display significantly larger variations with substitution. The ΔεHL of the siloles vary within 4.57–5.35 eV (ΔΔεHL = 0.78 eV) while for the 1,4-disilacyclohexa-2,5-dienes the range is 5.49–7.15 eV (ΔΔεHL = 1.66 eV). The excitation energy of the first allowed transitions display a moderate variation for siloles (3.60–4.41 eV) whereas the variation for 1,4-disilacyclohexa-2,5-dienes is nearly doubled (4.69–6.21 eV). Cyclobutadisiloles combine the characteristics of siloles and 1,4-disilacyclohexa-2,5-diene by having even lower excitation energies than siloles yet also extensive variation in excitation energies to substitution of 1,4-disilacyclohexa-2,5-dienes (3.47–4.77 eV, variation of 1.30 eV).

  • 13.
    Eklöf, Anders M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Guliashvili, Tamaz
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Relation between the π-Contribution to Reversed Si═C Bond Polarization and the Reaction Profile for the Thermolytic Formation of Silenes2008In: Organometallics, ISSN 0276-7333, E-ISSN 1520-6041, Vol. 27, no 20, p. 5203-5211Article in journal (Refereed)
    Abstract [en]

    A quantum chemical investigation of the reaction profiles for the thermal formation of silenes Z2Si═C(XSiH3)Y from silanes Z2(H3Si)Si−C(═X)Y (X = O, S, NMe; Y = NMe2, OMe, SMe, Me; Z = SiH3, Me) has been performed. Focus was put on the influence of the π-conjugative contribution to reversed Si═C bond polarization (Siδ−═Cδ+) as determined by natural resonance theory (NRT) at the B3LYP density functional theory level. Good linear correlations between the weights of π-conjugated reverse polarized resonance structures (ΣΦRP(π)) in the electronic structure and the Si═C bond lengths were found for the two classes of silenes with Z = SiH3 and Me (r2 = 0.957 and 0.955, respectively). Silenes that are strongly influenced by the π-conjugative reverse polarization have low barriers for back-reaction to the silanes, making these silenes more difficult to isolate when formed through a [1,3]-silyl shift than those that are naturally polarized. Modest exponential dependencies of the activation barriers for the reverse reactions on ΣΦRP(π) are found (r2 = 0.685 for Z = SiH3 and r2 = 0.699 for Z = Me). Species with the silyl groups replaced by trimethylsilyl groups, e.g., the Brook-type silene (Me3Si)2Si═C(OSiMe3)t-Bu, have lower contributions of ΣΦRP(π) by 3−23% than the corresponding model silenes, a result of steric bulk. The weight ΣΦRP(π) to the electronic structure of (Me3Si)2Si═C(OSiMe3)t-Bu was calculated to be 7.4%. With Z = Me, the silenes are in general not equally influenced by ΣΦRP(π) as with Z = SiH3, their energies relative to the silanes are higher, and they have higher activation barriers for both forward and backward reactions.

  • 14.
    Eklöf, Anders M
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Gullashvili, Tarnaz
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Relation between the pi-Contribution to Reversed Si=C Bond Polarization and the Reaction Profile for the Thermolytic Formation of Silenes2008In: Organometallics, ISSN 0276-7333, E-ISSN 1520-6041, Vol. 27, no 20, p. 5203-5211Article in journal (Refereed)
    Abstract [en]

    A quantum chemical investigation of the reaction profiles for the thermal formation of silenes Z(2)Si=C(XSiH3)Y from silanes Z(2)(H3Si)Si-C(=X)Y (X = O, S, NMe; Y = NMe2, OMe, SMe, Me; Z = SiH3, Me) has been performed. Focus was put on the influence of the pi-conjugative contribution to reversed Si=C bond polarization (Si delta-=C delta+) as determined by natural resonance theory (NRT) at the B3LYP density functional theory level. Good linear correlations between the weights of pi-conjugated reverse polarized resonance structures (Sigma Phi(RP)(pi)) in the electronic structure and the Si=C bond lengths were found for the two classes of silenes with Z = SiH3 and Me (r(2) = 0.957 and 0.955, respectively). Silenes that are strongly influenced by the pi-conjugative reverse polarization have low barriers for back-reaction to the silanes, making these silenes more difficult to isolate when formed through a [1,3]-silyl shift than those that are naturally polarized. Modest exponential dependencies of the activation barriers for the reverse reactions on Sigma Phi(RP)(pi) are found (r(2) = 0.685 for Z = SiH3 and r(2) = 0.699 for Z = Me). Species with the silyl groups replaced by trimethylsilyl groups, e.g., the Brook-type silene (Me3Si)(2)Si=C(OSi-Me-3)t-Bu, have lower contributions of Sigma Phi(RP)(pi) by 3-23% than the corresponding model silenes, a result of steric bulk. The weight Sigma Phi(RP)(pi) to the electronic structure of (Me3Si)(2)Si=C(OSiMe3)t-Bu was calculated to be 7.4%. With Z = Me, the silenes are in general not equally influenced by Sigma Phi(RP)(pi) as with Z = SiH3, their energies relative to the silanes are higher, and they have higher activation barriers for both forward and backward reactions.

  • 15.
    Eklöf, Anders M
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Effects of Substituents and Counterions on the Structures of Silenolates: A Computational Investigation2009In: Tetrahedron, ISSN 0040-4020, E-ISSN 1464-5416, Vol. 65, no 28, p. 5521-5526Article in journal (Refereed)
    Abstract [en]

    The structures and charge distributions of substituted silenolates   [H2SiC(=O)X](-) (X-H, SiH3, Me, t-Bu, OMe, NMe2; group A),  [Y2SiC(=O)H](-) (Y=H, F, Me, Ph, SiH3, SiMe3; group B), and [Y2SiC(=O)X](-) (Y=Me, X=t-Bu, and Y=SiMe3; X=t-Bu, OMe, NMe2; group C)   were examined through density functional theory calculations. The effects of the solvated counterion (K+, Li+, or MgCl+) and coordination site (O or Si) on the properties of group C silenolates were also Studied. The variation in the degree of pi-conjugative reverse SiC bond   polarization, Sigma Phi(RP)(pi) calculated by natural resonance theory,   was determined. The Sigma Phi(RP)(pi) correlated with r(SiC) for both   group A and B silenolates, and the correlation between Sigma   Phi(RP)(pi) and the Sum of valence angles at Si, Sigma alpha(Si), was   good for group A but poor for group B due to strong influence of the   inductive effect. The SiC charge difference correlated well with Sigma   Phi(RP)(pi) for group A, but not for group B, again an effect of   inductive substituent effects. The group C silenolates were Coordinated   to Li(THF)(3)(+), MgCl(THF)(4)(+), and K(THF)(5)(+) either via the O or   Si atom. The coordination energies show that coordination to the hard O   is preferred for Li+ and MgCl+, but the K+ ion coordinated   simultaneously to Si and O. Coordination of the solvated metal ion to O  resulted in shorter SiC bond length, an increased Sigma alpha(Si)   value, and lower Delta q(SiC) when compared to the naked silenolate.  Choice Of counterion and substituent provides a means to extensively vary the properties of silenolates such as their reactivity.

  • 16. Ekström, Ulf
    et al.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Norrman, Patrick
    Characterization of the Chemisorption of Methylsilane on a Au(1,1,1) Surface from the Silicon K- and L-Edge Spectra: A Theoretical Study Using the Four-Component Static Exchange Approximation2007In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 37, p. 13846-13850Article in journal (Refereed)
    Abstract [en]

    X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectra (NEXAFS) of methylsilane, isolated and chemisorbed to a Au(1,1,1) surface, are determined in the fully relativistic four-component static exchange approximationboth the K- and the L-edge of silicon are addressed in this investigation. In the fully chemisorbed structure, three H(Si) atoms have been cleaved off when Si binds in the hollow site of Au forming three Si−Au bonds of normal length. As due to the tri-coordinated chemisorption, the onsets of the K- and L-edge NEXAFS absorption bands occur some 2.0 and 2.5 eV lower in energy, respectively. The spin−orbit splittings in the silicon 2p-shell are not significantly changed due to adsorption. A partly chemisorbed methylsilane with only one H(Si) bond cleaved was also studied, and it is shown that the polarization dependence in the surface spectra contains details that can be used experimentally to identify the surface coordination of silicon. The red-shifts in the XPS silicon 1s (2p) spectra upon surface binding are 0.95 (0.65) and 1.15 (0.83) eV for the mono- and tricoordinated system, respectively.

  • 17.
    Emanuelsson, Rikard
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Denisova, Aleksandra
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Baumgartner, Judith
    Institut für Chemie, Universität Graz.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Optimization of the Cyclic Cross-Hyperconjugation in 1,4-Ditetrelcyclohexa-2,5-dienes2014In: Organometallics, ISSN 0276-7333, E-ISSN 1520-6041, Vol. 33, no 12, p. 2997-3004Article in journal (Refereed)
    Abstract [en]

    Cyclic cross-hyperconjugation can exist to variable extents in 1,4-ditetrelcyclohexa-2,5-dienes, i.e., all-carbon cyclohexa-1,4-dienes and 1,4-disila/digerma/distanna/diplumbacyclohexa-2,5-dienes. In this study we first use density functional theory (DFT) computations to optimize the conjugation strength by seeking the optimal atom E and substituent group E'Me-3 in the two saturated E(E'Me-3)(2) moieties (E and E' as the same or different tetrel (group 14) elements). We reveal that the all-carbon cyclohexadienes with gradually heavier E'Me-3 substituents at the two saturated carbon atoms display significant cross-hyperconjugation. The first electronic excitations in these compounds, which formally have two isolated C=C bonds, are calculated to reach wavelengths as long as 400 nm (excitation energies of 3.1 eV). These transitions are mostly forbidden, and the lowest allowed transitions are found at 387 nm (3.2 eV). The silicon analogues are also cross-hyperconjugated, while a decline is observed in the 1,4-digerma/distanna/diplumbacyclohexa-2,5-diene. Experiments on two substituted 1,4-disilacyclohexa-2,5-dienes confirm the effect of the E'Me3 substituents, with regard to both electronic excitations and geometries as determined by UV absorption spectroscopy and X-ray crystallography, respectively. At the end, we reveal through computations how electron-donating and electron-withdrawing substituents at the C=C double bonds influence the electronic properties of the all-carbon ring. We find that the first calculated excitation, which is forbidden, can be shifted to 440 nm (2.83 eV). This shows to what extent cyclic cross-hyperconjugation can affect the electronic and optical properties of a compound with two formally isolated C=C double bonds.

  • 18.
    Emanuelsson, Rikard
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Löfås, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Wallner, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry. Institut für Anorganische Chemie, Technische Universität Graz.
    Nauroozi, Djawed
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Baumgartner, Judith
    Institut für Anorganische Chemie, Technische Universität Graz.
    Marschner, Christoph
    Institut für Anorganische Chemie, Technische Universität Graz.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ott, Sascha
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Configuration- and Conformation-Dependent Electronic Structure Variations in 1,4-Disubstituted Cyclohexanes Enabled by a Carbon-to-Silicon Exchange2014In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 20, no 30, p. 9304-9311Article in journal (Other academic)
    Abstract [en]

    Cyclohexane, with its well-defined conformers, could be an ideal force-controlled molecular switch if it were to display substantial differences in electronic and optical properties between its conformers. We utilize sigma conjugation in heavier analogues of cyclohexanes (i.e. cyclohexasilanes) and show that 1,4-disubstituted cyclohexasilanes display configuration-and conformation-dependent variations in these properties. Cis- and trans-1,4-bis(trimethylsilylethynyl)-cyclohexasilanes display a 0.11 V difference in their oxidation potentials (computed 0.11 V) and a 0.34 eV difference in their lowest UV absorption (computed difference between first excitations 0.07 eV). This is in stark contrast to differences in the corresponding properties of analogous all-carbon cyclohexanes (computed 0.02 V and 0.03 eV, respectively). Moreover, the two chair conformers of the cyclohexasilane trans isomer display large differences in electronic-structure-related properties. This enables computational design of a mechanically force-controlled conductance switch with a calculated single-molecule ON/OFF ratio of 213 at zero-bias voltage.

  • 19.
    Emanuelsson, Rikard
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Löfås, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Zhu, Jun
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry. State Key Laboratory of Physical Chemistry of Solid Surfaces, Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    In Search of Flexible Molecular Wires with Near Conformer-Independent Conjugation and Conductance: A Computational Study2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 11, p. 5637-5649Article in journal (Refereed)
    Abstract [en]

    Oligomers of 1,4-disila/germa/stannacyclohexa-2,5-dienes as well as all-carbon 1,4-cyclohexadienes connected via E—E single bonds (E = C, Si, Ge, or Sn) were studied through quantum chemical calculations in an effort to identify conformationally flexible molecular wires that act as molecular “electrical cords” having conformer-independent conjugative and conductive properties. Our oligomers display neutral hyperconjugative interactions (σ/π-conjugation) between adjacent σ(E—E) and π(C═C) bond orbitals, and these interactions do not change with conformation. The energies and spatial distributions of the highest occupied molecular orbitals of methyl-, silyl-, and trimethylsilyl (TMS)-substituted 1,4-disilacyclohexa-2,5-diene dimers, and stable conformers of trimers and tetramers, remain rather constant upon Si–Si bond rotation. Yet, steric congestion may be a concern in some of the oligomer types. The calculated conductances for the Si-containing tetramers are similar to that of a σ-conjugated linear all-anti oligosilane (a hexadecasilane) with equally many bonds in the conjugated paths. Moreover, the Me-substituted 1,4-disilacyclohexadiene tetramer has modest conductance fluctuations with Si–Si bond rotations when the electrode–electrode distance is locked (variation by factor 30), while the fluctuations under similar conditions are larger for the analogous TMS-substituted tetramer. When the electrode–electrode distance is changed several oligomers display small conductance variations within certain distance intervals, e.g., the mean conductance of TMS-substituted 1,4-disilacyclohexa-2,5-diene tetramer is almost unchanged over 9 Å of electrode–electrode distances.

  • 20.
    Emanuelsson, Rikard
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Tibbelin, Julius
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Wallner, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Smith, Joshua R.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Strong neutral cross-hyperconjugation and linear hyperconjugation enabled by saturated Group 14 element E(E ' R-3)(2), (E ' R-3)E-E(E ' R-3), and E(E ' R-2)(2)E segments2013In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 245, p. 1246-INOR-Article in journal (Other academic)
  • 21.
    Emanuelsson, Rikard
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Wallner, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Ng, Eugene A. M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Smith, J. R.
    Nauroozi, Djawed
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Ott, Sascha
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Cross-hyperconjugation: An unexplored orbital interaction between pi-conjugated and saturated molecular segments2013In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 52, no 3, p. 983-987Article in journal (Refereed)
    Abstract [en]

    Crossing a barrier: Molecules with saturated ER2 units (E=C or Si, R=electron-releasing group) inserted between two π-conjugated segments have electronic and optical properties that resemble those of cross-conjugated molecules (see figure). This cross-hyperconjugation provides a deeper understanding of the conjugation phenomenon, and is an alternative to cross-conjugation in the design of molecules for nano and materials applications.

  • 22. Finke, Aaron D.
    et al.
    Jahn, Burkhard O.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Saithalavi, Anas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Dahlstrand, Christian
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Nauroozi, Djawed
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Haberland, Sophie
    Gisselbrecht, Jean-Paul
    Boudon, Corinne
    Mijangos, Edgar
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Schweizer, W. Bernd
    Ott, Sascha
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Diederich, Francois
    The 6,6-Dicyanopentafulvene Core: A Template for the Design of Electron-Acceptor Compounds2015In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 21, no 22, p. 8168-8176Article in journal (Refereed)
    Abstract [en]

    The electron-accepting ability of 6,6-dicyanopentafulvenes (DCFs) can be varied extensively through substitution on the five-membered ring. The reduction potentials for a set of 2,3,4,5-tetraphenyl-substituted DCFs, with varying substituents at the para-position of the phenyl rings, strongly correlate with their Hammett sigma(p)-parameters. By combining cyclic voltammetry with DFT calculations ((U)B3LYP/6-311+G(d)), using the conductor-like polarizable continuum model (CPCM) for implicit solvation, the absolute reduction potentials of a set of twenty DCFs were reproduced with a mean absolute deviation of 0.10eV and a maximum deviation of 0.19eV. Our experimentally investigated DCFs have reduction potentials within 3.67-4.41eV, however, the computations reveal that DCFs with experimental reduction potentials as high as 5.3eV could be achieved, higher than that of F-4-TCNQ (5.02eV). Thus, the DCF core is a template that allows variation in the reduction potentials by about 1.6eV.

  • 23.
    Guliashvili, Tamaz
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Tibbelin, Julius
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Ryu, Jiyeon
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Unsuccessful attempts to add alcohols to transient 2-amino-2-siloxy- silenes - leading to a new benign route for base-free alcohol protection2010In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 39, no 39, p. 9379-9385Article in journal (Refereed)
    Abstract [en]

    Thermolytic formation of transient   1,1-bis(trimethylsilyl)-2-dimethylamino-2-trimethylsiloxysilene (2)  from N,N-dimethyl(tris(trimethylsilyl) silyl) methaneamide (1) in presence of a series of alcohols was investigated. The products are,  however, not the expected alcohol-silene addition adducts but   silylethers formed in nearly quantitative yields. Thermolysis of 1 in   the presence of both alcohols (MeOH or iPrOH) and 1,3-dienes   (1,3-butadiene or 2,3-dimethyl-1,3-butadiene) gives   alkyl-tris(trimethylsilyl)silylethers and the [4+2] cycloadducts   between the silene and diene, which confirms the presence of 2 and that   it is unreactive towards alcohols. The observed silylethers are substitution adducts where the amide group of the silylamide is replaced by an alkoxy group, and the reaction time is reflected in the   steric bulk of the alcohol. Indeed, the formation of silylethers from   the reaction of alcohols with silylamide represents a new base-free   method for protection of alcohols. The protection reactions using 1   progresses at elevated temperatures, or alternatively, under acid   catalysis at ambient temperature, and similar protections can be   carried out with N-cyclohexyl(triphenylsilyl) methaneamide and N,   N-dimethyl(trimethylsilyl) methaneamide. The latter silylamide can be used under neutral conditions at room temperature. The only by-products  are formamides (N,N-dimethylformamide (DMF) or N-cyclohexylformamide), and the reactions can be performed without solvent. In addition to alcohols we also examined the method for protection of diols, thiols   and carboxylic acids,and also these reactions proceeded in high yields and with good selectivities.

  • 24.
    Göransson, Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Emanuelsson, Rikard
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Jorner, Kjell
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Markle, Todd F.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Charge transfer through cross-hyperconjugated versus cross-pi-conjugated bridges: an intervalence charge transfer study2013In: Chemical Science, ISSN 2041-6520, Vol. 4, no 9, p. 3522-3532Article in journal (Refereed)
    Abstract [en]

    Recently there has been much interest in electron transfer and transport through cross-conjugated molecules as interesting test cases for the interplay between molecular and electronic structure as well as potential motifs in the design of new compounds for molecular electronics. Herein we expand on this concept and present the synthesis and characterization of a series of four organic mixed-valence dyads to probe the effect of the bridge structure on the electronic coupling. The electronic coupling between two triarylamine units could be mediated either by cross-hyperconjugation through a saturated ER2 bridge (E = C or Si, R = alkyl or silyl group), or via a cross-conjugated pi-system. The aim of the study is to compare the electron transfer through the various saturated bridges to that of a cross-pi-conjugated bridge. The electronic coupling in these mixed-valence compounds was determined by analysis of intervalence charge transfer bands, and was found to be in the range of 100-400 cm(-1). A complementary DFT and TD-DFT study indicated that the electronic coupling in the dyads with saturated ER2 segments is highly conformer dependant. Furthermore, the calculations showed that two types of interactions contribute to the electronic coupling; a through-bond cross-(hyper)conjugation mechanism and a through-space mechanism. Taken together, these findings suggest the possibility for new architectures for molecular electronics applications utilizing cross-hyperconjugation through properly selected saturated segments which have comparable electron transfer characteristics as regular cross-pi-conjugated molecules.

  • 25.
    Hertting, Nils
    et al.
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Institute for Housing and Urban Research.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Case Uppsala, Campus Polacksbacken:  Location, surrounding, stakeholders2017In: Dreams and Seeds. The Role of Campuses and Sustainable Urban Development / [ed] Schewenius, Keränen, al Rawaf, Stockholm: Stockholm Resilience Center , 2017, p. 51-55Chapter in book (Other (popular science, discussion, etc.))
  • 26.
    Jafri, Hassan M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Löfås, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jonas, Fransson
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Blom, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Wallner, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry, Physical Organic Chemistry.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Identification of vibrational signatures from short chains of interlinked molecule-nanoparticle junctions obtained by inelastic electron tunnelling spectroscopy2013In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 5, no 11, p. 4673-4677Article in journal (Refereed)
    Abstract [en]

    Short chains containing a series of metal- molecule-nanoparticle nanojunctions are a nano-materials system with the potential to give electrical signatures close to those from single molecule experiments while enabling to build portable devices on a chip. Inelastic electron tunnelling spectroscopy (IETS) measurements provide one of the most characteristic electrical signals of single and few molecules. In interlinked molecule-nanoparticle (NP) chains containing of typically 5-7 molecules in a chain, the spectrum is expected to be a superposition of the vibrational signature of individual molecules. We have established a stable and reproducible molecule-AuNP multi-junction by placing few 1,8-octanedithiol (ODT) molecules into a versatile and portable nanoparticle-nanoelectrode platform and measured for the first time vibrational molecular signatures complex and coupled few-molecule-NP junctions. From quantum transport calculations, we model the IETS spectra and identify vibrational modes as well as the number of molecules contributing to the electron transport in the measured spectra.

  • 27.
    Jafri, S Hassan M
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Blom, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Wallner, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Welch, Ken
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Strømme, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Control of junction resistances in molecular electronic devices fabricated by FIB2011In: Microelectronic Engineering, ISSN 0167-9317, E-ISSN 1873-5568, Vol. 88, no 8, p. 2629-2631Article in journal (Refereed)
    Abstract [en]

    A major hurdle to realize molecular electronic devices (MEDs) is to make reliable electrical contacts to a single or a few molecules. Our nano-contact platform with a gap size of less than 25 nm with resistances above 1000 TΩ was built using combined techniques of photolithography, electron beam lithography and focused ion beam milling. In this study, we have used gold nanoparticles (AuNPs) to bridge the nanoelectrode gaps by dielectrophoretic trapping and thus obtain electrical contacts. The electrodes and/or the nanoparticles were functionalised with 1–2 nm long alkane-thiol molecules so that the electronic structure of these molecules determines the properties of the electrical junction. Molecules were introduced both by functionalising the nanogap and the nanoparticles and the results of both functionalisation protocols are compared. Here, we show the nanogap–nanoparticle bridge set-up containing metal–molecule junctions that can be used as a base for the development of molecular electronics containing only a few molecules under ambient conditions. Current–voltage (IV) characterization of alkanethiol/gold junction showed non-linear response where mean geometric resistance of four different junctions could be tuned from 20 GΩ to 20 TΩ. The results from the measurements on 1-alkanethiol in such devices is a first step to demonstrate that this platform has the potential to obtain stable electronic devices having relatively small numbers of molecules with reliable metal molecule junction by combing top-down and bottom-up approaches.

  • 28.
    Jafri, S. Hassan M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. Department of Electrical Engineering, Mirpur University of Science and Technology, Pakistan.
    Löfås, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Uppsala Univ, Dept Phys & Astron, SE-75120 Uppsala, Sweden..
    Blom, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Wallner, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC. Uppsala Univ, Dept Chem BMC, SE-75123 Uppsala, Sweden..
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Nano-fabrication of molecular electronic junctions by targeted modification of metal-molecule bonds2015In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, article id 14431Article in journal (Refereed)
    Abstract [en]

    Reproducibility, stability and the coupling between electrical and molecular properties are central challenges in the field of molecular electronics. The field not only needs devices that fulfill these criteria but they also need to be up-scalable to application size. In this work, few-molecule based electronics devices with reproducible electrical characteristics are demonstrated. Our previously reported 5 nm gold nanoparticles (AuNP) coated with omega-triphenylmethyl (trityl) protected 1,8-octanedithiol molecules are trapped in between sub-20 nm gap spacing gold nanoelectrodes forming AuNP-molecule network. When the trityl groups are removed, reproducible devices and stable Au-thiol junctions are established on both ends of the alkane segment. The resistance of more than 50 devices is reduced by orders of magnitude as well as a reduction of the spread in the resistance histogram is observed. By density functional theory calculations the orders of magnitude decrease in resistance can be explained and supported by TEM observations thus indicating that the resistance changes and strongly improved resistance spread are related to the establishment of reproducible and stable metal-molecule bonds. The same experimental sequence is carried out using 1,6-hexanedithiol functionalized AuNPs. The average resistances as a function of molecular length, demonstrated herein, are comparable to the one found in single molecule devices.

  • 29.
    Jafri, Syed Hassan Mujtaba
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Blom, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Wallner, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Stability optimisation of molecular electronic devices based on nanoelectrode-nanoparticle bridge platform in air and different storage liquids2014In: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896X, Vol. 16, no 12, p. 2811-Article in journal (Refereed)
    Abstract [en]

    The long-term stability of metal nanoparticle-molecule junctions in molecular electronic devices based on nanoelectrodes (NEL) is a major challenge in the effort to bring related molecular electronic devices to application. To optimize the reproducibility of molecular electronic nanodevices, the time-dependent modification of such junctions as exposed to different media needs to be known. Here, we have studied (1) the stability of Au-NEL and (2) the electrical stability of molecule-Au nanoparticle (AuNP) junctions themselves with the molecule being 1,8-octanedithiol (ODT). Both the NELs only and the junctions were exposed to air and liquids such as deionized water, tetrahydrofuran, toluene and tetramethylethylenediamine (TMEDA) over a period of 1 month. The nanogaps remained stable in width when stored in either deionized water or toluene, whereas the current through 1,8-octanedithiol-NP junctions remained most stable when stored in TMEDA as compared to other solvents. Although it is difficult to follow the chemical processes in such devices in the 10-nm range with analytical methods, the behavior can be interpreted from known interactions of solvent molecules with electrodes and ODT.

  • 30.
    Jahn, Burkhard O.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Galperin, Michael
    Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California 92093, United States.
    Fransson, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Organic Single Molecular Structures for Light Induced Spin-Pump Devices2013In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 7, no 2, p. 1064-1071Article in journal (Refereed)
    Abstract [en]

    We present theoretical results on molecular structures for realistic spin-pump applications. Taking advantage of the electron spin resonance concept, we find that interesting candidates constitute triplet biradicals with two strongly spatially and energetically separated singly occupied molecular orbitals (SOMOs). Building on earlier reported stable biradicals, particularly bis(nitronyl nitroxide) based biradicals, we employ density functional theory to design a selection of potential molecular spin-pumps which should be persistent at ambient conditions. We estimate that our proposed molecular structures will operate as spin-pumps using harmonic magnetic fields in the MHz regime and optical fields in the infrared to visible light regime.

  • 31. Jiang, Jun
    et al.
    Smith, Joshua R.
    Luo, Yi
    Grennberg, Helena
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Multidecker Bis(benzene)chromium: Opportunities for Design of Rigid and Highly Flexible Molecular Wires2011In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 3, p. 785-790Article in journal (Refereed)
    Abstract [en]

    On the basis of density functional theory calculations, we have designed three classes of multidecker bis(benzene)chromium molecular wires with -(arene-chromium(0)-arene)- sandwich complexes as monomer units. The arene fragments of the wires are either [2.2]paracyclophane (class-1), biphenylene (class-2), or biphenyl (class-3) compounds with two strongly coupled benzene rings. The wires are rigid (class-1) or highly flexible (class-3), and they are realistic synthetic targets as the bonding at each Cr-(0) atom satisfies the 18-electron rule. The Cr-(0) atoms couple strongly with the arene units giving a "quasi-band" that stems from the highest occupied molecular orbital (HOMO) of the monomers, a HOMO sub-band in which the orbitals are highly delocalized indicating metal/pi-conjugation. Moreover, the HOMO energies are close to the Fermi energy of the metal electrodes used (Zn(111)), and therefore, injected electrons can easily tunnel through the wires. The metal of the electrodes was selected so that its Fermi level is located slightly above the HOMO energies of the wires. High conductivity and very slow decay of conductance with increased length are found for all three wire classes, making them suitable for molecular electronics applications. Class-2 and class-3 wires display high conformational flexibilities and, simultaneously, only modest conformational dependence of the conductance. These wires therefore function as molecular electrical cords, i.e., molecules which are easily twisted and coiled and for which the conductance displays only modest conformational dependence.

  • 32.
    Jorner, Kjell
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Dreos, Ambra
    Chalmers, Dept Chem & Chem Engn, Kemigarden 4, SE-41296 Gothenburg, Sweden..
    Emanuelsson, Rikard
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    El Bakouri, Ouissam
    Univ Girona, Dept Quim, IQCC, Campus Montilivi, Girona 17003, Spain..
    Fernández Galván, Ignacio
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry. Uppsala Univ, UC3, Box 523, SE-75120 Uppsala, Sweden..
    Borjesson, Karl
    Chalmers, Dept Chem & Chem Engn, Kemigarden 4, SE-41296 Gothenburg, Sweden.;Univ Gothenburg, Dept Chem & Mol Biol, Kemigarden 4, SE-41296 Gothenburg, Sweden..
    Feixas, Ferran
    Univ Girona, Dept Quim, IQCC, Campus Montilivi, Girona 17003, Spain..
    Lindh, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry. Uppsala Univ, UC3, Box 523, SE-75120 Uppsala, Sweden..
    Zietz, Burkhard
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Moth-Poulsen, Kasper
    Chalmers, Dept Chem & Chem Engn, Kemigarden 4, SE-41296 Gothenburg, Sweden..
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Unraveling factors leading to efficient norbornadiene-quadricyclane molecular solar-thermal energy storage systems2017In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 5, no 24, p. 12369-12378Article in journal (Refereed)
    Abstract [en]

    Developing norbornadiene-quadricyclane (NBD-QC) systems for molecular solar-thermal (MOST) energy storage is often a process of trial and error. By studying a series of norbornadienes (NBD-R-2) doubly substituted at the C7-position with R = H, Me, and iPr, we untangle the interrelated factors affecting MOST performance through a combination of experiment and theory. Increasing the steric bulk along the NBD-R-2 series gave higher quantum yields, slightly red-shifted absorptions, and longer thermal lifetimes of the energy-rich QC isomer. However, these advantages are counterbalanced by lower energy storage capacities, and overall R = Me appears most promising for short-term MOST applications. Computationally we find that it is the destabilization of the NBD isomer over the QC isomer with increasing steric bulk that is responsible for most of the observed trends and we can also predict the relative quantum yields by characterizing the S-1/S-0 conical intersections. The significantly increased thermal half-life of NBD-iPr(2) is caused by a higher activation entropy, highlighting a novel strategy to improve thermal half-lives of MOST compounds and other photo-switchable molecules without affecting their electronic properties. The potential of the NBD-R-2 compounds in devices is also explored, demonstrating a solar energy storage efficiency of up to 0.2%. Finally, we show how the insights gained in this study can be used to identify strategies to improve already existing NBD-QC systems.

  • 33.
    Jorner, Kjell
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Emanuelsson, Rikard
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Ayub, Rabia
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Denisova, Aleksandra
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Siloles and cyclopentadienes as "aromatic chameleons" influenced by aromaticity in both the ground state and lowest electronically excited states2014In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 247, article id 560-ORGNArticle in journal (Other academic)
  • 34.
    Jorner, Kjell
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Emanuelsson, Rikard
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Dahlstrand, Christian
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Tong, Hui
    Denisova, Aleksandra V.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Impact of Ground- and Excited-State Aromaticity on Cyclopentadiene and Silole Excitation Energies and Excited-State Polarities2014In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 20, no 30, p. 9295-9303Article in journal (Refereed)
    Abstract [en]

    A new qualitative model for estimating the properties of substituted cyclopentadienes and siloles in their lowest pi pi* excited states is introduced and confirmed through quantum chemical calculations, and then applied to explain earlier reported experimental excitation energies. According to our model, which is based on excited-state aromaticity and antiaromaticity, siloles and cyclopentadienes are cross-hyperconjugated "aromatic chameleons" that adapt their electronic structures to conform to the various aromaticity rules in different electronic states (Huckel's rule in the pi(2) electronic ground state (S-0) and Baird's rule in the lowest pi pi* excited singlet and triplet states (S-1 and T-1)). By using pen-and-paper arguments, one can explain polarity changes upon excitation of substituted cyclopentadienes and siloles, and one can tune their lowest excitation energies by combined considerations of ground-and excited-state aromaticity/antiaromaticity effects. Finally, the "aromatic chameleon" model can be extended to other monocyclic compound classes of potential use in organic electronics, thereby providing a unified view of the S-0, T-1, and S-1 states of a range of different cyclic cross-pi-conjugated and cross-hyperconjugated compound classes.

  • 35.
    Jorner, Kjell
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Feixas, Ferran
    Univ Girona, IQCC, Campus Montilivi S-N, Girona 17071, Catalonia, Spain.;Univ Girona, Dept Quim, Campus Montilivi S-N, Girona 17071, Catalonia, Spain..
    Ayub, Rabia
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Lindh, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry. Uppsala Univ, Uppsala Ctr Computat Chem UC3, Box 518, S-75120 Uppsala, Sweden..
    Sola, Miquel
    Univ Girona, IQCC, Campus Montilivi S-N, Girona 17071, Catalonia, Spain.;Univ Girona, Dept Quim, Campus Montilivi S-N, Girona 17071, Catalonia, Spain..
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Analysis of a Compound Class with Triplet States Stabilized by Potentially Baird Aromatic [10]Annulenyl Dicationic Rings2016In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 22, no 8, p. 2793-2800Article in journal (Refereed)
    Abstract [en]

    The low-lying triplet state of a recently published compound (TMTQ) was analyzed quantum chemically in light of suggestions that it is influenced by Baird aromaticity. Two mesomeric structures describe this state: 1)a zwitterionic Baird aromatic structure with a triplet diradical 8-electron methano[10]annulene (M10A) dicationic ring and 2)a Huckel aromatic with a neutral closed-shell 10-electron ring. According to charge and spin density distributions, the Huckel aromatic structure dominates the triplet state (the Baird aromatic contributes at most 12%), and separation of the aromatic fluctuation index (FLU) into and electron contributions emphasizes this finding. The small singlet-triplet energy gap is due to Huckel aromaticity of the M10A ring, clarified by comparison to the smaller analogues of TMTQ. Yet, TMTQ and its analogues are Huckel-Baird hybrids allowing for tuning between closed-shell 4n+2 Huckel aromaticity and open-shell 4n Baird aromaticity.

  • 36.
    Jorner, Kjell
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Jahn, Burkhard O.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC. SciClus GmbH & Co. KG, Moritz-von-Rohr-Str. 1a, 07745 Jena, Germany .
    Bultinck, Patrick
    SciClus GmbH & Co. KG, Moritz-von-Rohr-Str. 1a, 07745 Jena, Germany.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Triplet state homoaromaticity: concept, computational validation and experimental relevance2018In: Chemical Science, ISSN 2041-6520, E-ISSN 2041-6539, Vol. 9, no 12, p. 3165-3176Article in journal (Refereed)
    Abstract [en]

    Cyclic conjugation that occurs through-space and leads to aromatic properties is called homoaromaticity. Here we formulate the homoaromaticity concept for the triplet excited state (T1) based on Baird's 4n rule and validate it through extensive quantum-chemical calculations on a range of different species (neutral, cationic and anionic). By comparison to well-known ground state homoaromatic molecules we reveal that five of the investigated compounds show strong T1 homoaromaticity, four show weak homoaromaticity and two are non-aromatic. Two of the compounds have previously been identified as excited state intermediates in photochemical reactions and our calculations indicate that they are also homoaromatic in the first singlet excited state. Homoaromaticity should therefore have broad implications in photochemistry. We further demonstrate this by computational design of a photomechanical “lever” that is powered by relief of homoantiaromatic destabilization in the first singlet excited state.

  • 37.
    Kato, Haruhisa
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry. Department of Biochemistry and Organic Chemistry, Organic Chemistry II.
    Brink, Maria
    Möllerstedt, Helene
    Piqueras, Mari Carmen
    Crespo, Raül
    Ottosson, Henrik
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry. Department of Biochemistry and Organic Chemistry, Organic Chemistry II.
    J. Org. Chem.2005In: J. Org. Chem., no 70, p. 9495-9504Article in journal (Refereed)
  • 38. Kivimaeki, A.
    et al.
    Norman, P.
    Coreno, M.
    de Simone, M.
    Grazioli, C.
    Totani, R.
    Ressel, B.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Puglia, Carla
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Use of two-dimensional photoelectron spectroscopy in the decomposition of an inner-shell excitation spectrum broadened by super-Coster-Kronig decay2013In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 88, no 6, p. 062502-Article in journal (Refereed)
    Abstract [en]

    The Ge 3p core excitation spectrum of the n-butylgermane molecule only reveals two peaks, whereas the rest of the fine structure is obscured due to the large lifetime broadenings of core-excited states. A two-dimensional presentation of resonant photoemission spectra allows us to observe some other resonances. The interpretation of experimental results is supported by ab initio calculations conducted at the four-component relativistic level of theory with full account made for spin-orbit interactions already in the zeroth-order Hamiltonian.

  • 39.
    Leifer, Klaus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Blom, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jafri, Hassan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Löfås, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Wallner, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Use of a nanoelectrode nanoparticle bridge platform in molecular electronics2010In: ElecMol’10, 5th International Meeting on Molecular Electronics, Grenoble, France, December 6-10, 2010, 2010, p. 116-116Conference paper (Refereed)
  • 40.
    Lundstedt, Anna
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Papadakis, Raffaello
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Li, Hu
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Han, Yuanyuan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Bergman, Joakim
    AstraZeneca R&D Mölndal, Medicinal Chemistry.
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Grennberg, Helena
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    White-light photoassisted covalent functionalization of graphene using 2-propanol2017In: Small Methods, ISSN 2366-9608, Vol. 1, no 11, article id 1700214Article in journal (Refereed)
    Abstract [en]

    Herein, a photochemical method for functionalization of graphene using 2-propanol is reported. The functionalization method which is catalyst-free operates at ambient temperature in neat 2-propanol under an inert atmosphere of argon. The equipment requirement is a white-light source for the irradiation. The same methodology when applied to kish graphite results in a novel material, exhibiting significantly higher wettability than the starting material according to water contact angle measurements. Furthermore, the materials generated from both graphene and kish graphite exhibit increased adhesion energy, attributed to the fixation of isopropyl alcohol fragments onto graphene and graphite, respectively. The presence of hydroxyl groups and the possibility for further reactions on the functionalized graphene material are demonstrated through a substitution reaction with thionyl chloride, where the hydroxyl groups are replaced with chlorides, as confirmed through X-ray photoelectron spectroscopy analysis.

  • 41.
    Löfås, Henrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Emanuelsson, Rikard
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Conductance through Carbosilane Cage Compounds: A Computational Investigation2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 42, p. 21692-21699Article in journal (Refereed)
    Abstract [en]

    Silicon is still the dominating material in microelectronics, yet primarily π-conjugated hydrocarbons are investigated in the field of single-molecule electronics even though linear oligosilanes are σ-conjugated. A drawback with the latter is their high conformational flexibility which strongly affects conductance. Here we report on a first principles density functional theory investigation of a series of rigid [2.2.2]bicyclic carbosilanes with 3, 2, 1, or 0 disilanylene bridges, providing all-silicon paths for charge transport. It is explored if these paths can be seen as independent and equivalent current paths acting as parallel resistors. For high conductance through the carbosilanes they need to be anchored to the gold electrodes via groups that are matched with the σ-conjugated paths of the oligosilane cage segment, and we find that silyl (SiH3) groups are better matched than thiophenol groups. Even for the carbosilane with three disilanylene bridges we find that the most transmitting conductance channel is not equally distributed on the three parallel bridges. In addition, there is significant communication between the various pathways, which results in destructive interference lowering the conductance. Taken together, the different disilanylene bridges in the cage compounds do not act as parallel resistors.

  • 42.
    Löfås, Henrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jahn, B. O.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Wärnå, John
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Emanuelsson, Rikard
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    A computational study of potential molecular switches that exploit Baird's rule on excited-state aromaticity and antiaromaticity2014In: Faraday discussions (Online), ISSN 1359-6640, E-ISSN 1364-5498, Vol. 174, p. 105-124Article in journal (Refereed)
    Abstract [en]

    A series of tentative single-molecule conductance switches which could be triggered by light were examined by computational means using density functional theory (DFT) with non-equilibrium Green's functions (NEGF). The switches exploit the reversal in electron counting rules for aromaticity and antiaromaticity upon excitation from the electronic ground state (S0) to the lowest [small pi][small pi]* excited singlet and triplet states (S1 or T1), as described by Huckel's and Baird's rules, respectively. Four different switches and one antifuse were designed which rely on various photoreactions that either lead from the OFF to the ON states (switches 1, 2 and 4, and antifuse 5) or from the ON to the OFF state (switch 3). The highest and lowest ideal calculated switching ratios are 1175 and 5, respectively, observed for switches 1 and 4. Increased thermal stability of the 1-ON isomer is achieved by benzannulation (switch 1B-OFF/ON). The effects of constrained electrode-electrode distances on activation energies for thermal hydrogen back-transfer from 1-ON to 1-OFF and the relative energies of 1-ON and 1-OFF at constrained geometries were also studied. The switching ratio is strongly distance-dependent as revealed for 1B-ON/OFF where it equals 711 and 148 when the ON and OFF isomers are calculated in electrode gaps with distances confined to either that of the OFF isomer or to that of the ON isomer, respectively.

  • 43.
    Löfås, Henrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Orthaber, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Jahn, Burkhard O.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Rouf, Alvi M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ott, Sascha
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    New Class of Molecular Conductance Switches Based on the [1,3]-Silyl Migration from Silanes to Silenes2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 21, p. 10909-10918Article in journal (Refereed)
    Abstract [en]

    Based on first principles density functional theory calculations we propose a new molecularphotoswitch which exploits a photochemical [1,3]-silyl(germyl) shift leading from a silane to asilene (a Si=C double bonded compound). The silanes investigated herein act as the OFF state,with tetrahedral saturated silicon atoms disrupting the conjugation through the molecules. Thesilenes, on the other hand, have conjugated paths spanning over the complete molecules, andthus act as the ON state. We calculate ON/OFF conductance ratios in the range of 10 - 50at a voltage of +1 V. In the low bias regime the ON/OFF ratio increases to a range of 200 -1150. The reverse reaction could be triggered thermally or photolytically, with the silenebeing slightly higher in relative energy than the silane. The calculated activation barriers forthe thermal back-rearrangement of the migrating group can be tuned, and are in the range 108 -171 kJ/mol for the switches examined herein. The first principles calculations together witha simple one-level model shows that the high ON/OFF ratio in the molecule assembled in asolid state device is due to changes in the energy position of the frontier molecular orbitalscompared to the Fermi energy of the electrodes, in combination with an increased effectivecoupling between the molecule and the electrodes for the ON state.

  • 44.
    Lüder, Johann
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Puglia, Carla
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Many-body effects and excitonic features in 2D biphenylene carbon2016In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 144, no 2, article id 024702Article in journal (Refereed)
    Abstract [en]

    The remarkable excitonic effects in low dimensional materials in connection to large binding energies of excitons are of great importance for research and technological applications such as in solar energy and quantum information processing as well as for fundamental investigations. In this study, the unique electronic and excitonic properties of the two dimensional carbon network biphenylene carbon were investigated with GW approach and the Bethe-Salpeter equation accounting for electron correlation effects and electron-hole interactions, respectively. Biphenylene carbon exhibits characteristic features including bright and dark excitons populating the optical gap of 0.52 eV and exciton binding energies of 530 meV as well as a technologically relevant intrinsic band gap of 1.05 eV. Biphenylene carbon's excitonic features, possibly tuned, suggest possible applications in the field of solar energy and quantum information technology in the future.

  • 45.
    Messersmith, Reid E.
    et al.
    Johns Hopkins Univ, Dept Chem, 3400 North Charles St, Baltimore, MD 21218 USA..
    Yadav, Sangeeta
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Siegler, Maxime A.
    Johns Hopkins Univ, Dept Chem, 3400 North Charles St, Baltimore, MD 21218 USA..
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Tovar, John D.
    Johns Hopkins Univ, Dept Chem, 3400 North Charles St, Baltimore, MD 21218 USA.;Johns Hopkins Univ, Dept Mat Sci & Engn, 3400 North Charles St, Baltimore, MD 21218 USA..
    Benzo[b]thiophene Fusion Enhances Local Borepin Aromaticity in Polycyclic Heteroaromatic Compounds2017In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 82, no 24, p. 13440-13448Article in journal (Refereed)
    Abstract [en]

    This report documents the synthesis, characterization, and computational evaluation of two isomeric borepin-containing polycyclic aromatics. The syntheses of these two isomers involved symmetrical disubstituted alkynes that were reduced to Z-olefins followed by borepin formation either through an isolable stannocycle intermediate or directly from the alkene via the trapping of a transient dilithio intermediate. Comparisons of their magnetic, crystallographic, and computational characterization to literature compounds gave valuable insights about the aromaticity of these symmetrically fused [b,f]borepins. The fusion of benzo[b]thiophene units to the central borepin cores forced a high degree of local aromaticity within the borepin moieties relative to other known borepin-based polycyclic aromatics. Each isomer had unique electronic responses in the presence of fluoride anions. The experimental data demonstrate that the local borepin rings in these two compounds have a relatively high amount of aromatic character. Results from quantum chemical calculations provide a more comprehensive understanding of local and global aromatic characters of various rings in fused ring systems built upon boron heterocycles.

  • 46.
    Mohamed, Rana K.
    et al.
    Florida State Univ, Dept Chem & Biochem, Tallahassee, FL 32310 USA..
    Mondal, Sayantan
    Florida State Univ, Dept Chem & Biochem, Tallahassee, FL 32310 USA..
    Jorner, Kjell
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Delgado, Thais Faria
    Florida State Univ, Dept Chem & Biochem, Tallahassee, FL 32310 USA..
    Lobodin, Vladislav V.
    Natl High Magnet Field Lab, Tallahassee, FL 32310 USA.;Florida State Univ, Future Fuels Inst, Tallahassee, FL 32310 USA..
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Alabugin, Igor V.
    Florida State Univ, Dept Chem & Biochem, Tallahassee, FL 32310 USA..
    The Missing C-1-C-5 Cycloaromatization Reaction: Triplet State Antiaromaticity Relief and Self-Terminating Photorelease of Formaldehyde for Synthesis of Fulvenes from Enynes2015In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 137, no 49, p. 15441-15450Article in journal (Refereed)
    Abstract [en]

    The last missing example of the four archetypical cycloaromatizations of enediynes and enynes was discovered by combining a twisted alkene excited state with a new self-terminating path for intramolecular conversion of diradicals into closed-shell products. Photoexcitation of aromatic enynes to a twisted alkene triplet state creates a unique stereoelectronic situation, which is facilitated by the relief of excited state antiaromaticity of the benzene ring. This enables the usually unfavorable 5-endo-trig cyclization and merges it with 5-exo-dig closure. The 1,4-diradical product of the C1-C5 cyclization undergoes internal H atom transfer that is coupled with the fragmentation of an exocyclic C-C bond. This sequence provides efficient access to benzofulvenes from enynes and expands the utility of self-terminating aromatizing enyne cascades to photochemical reactions. The key feature of this self-terminating reaction is that, despite the involvement of radical species in the key cyclization step, no external radical sources or quenchers are needed to provide the products. In these cascades, both radical centers are formed transiently and converted to the closed-shell products via intramolecular H-transfer and C-C bond fragmentation. Furthermore, incorporating C-C bond cleavage into the photochemical self-terminating cyclizations of enynes opens a new way for the use of alkenes as alkyne equivalents in organic synthesis.

  • 47. Möllerstedt, Helene
    et al.
    Piqueras, Mari Carmen
    Crespo, Raül
    Ottosson, Henrik
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Chemistry. Organisk kemi.
    Fulvenes, Fulvalenes, and Azulene: Are They Aromatic Chameleons?2004In: J. Am. Chem. Soc., p. 1.9-Article in journal (Refereed)
  • 48. Oh, Juwon
    et al.
    Sung, Young Mo
    Mori, Hirotaka
    Park, Seongchul
    Jorner, Kjell
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Lim, Manho
    Osuka, Atsuhiro
    Kim, Dongho
    Unraveling Excited-Singlet-State Aromaticity via Vibrational Analysis2017In: Chem, ISSN 24519294, Vol. 3, no 5, p. 870-880Article in journal (Refereed)
    Abstract [en]

    Summary

    The concept of excited-state aromaticity is receiving much attention in that completely reversed aromaticity in the excited state (so-called aromaticity reversal) provides crucial insight into photostability, photoreactivity, and its application to the photosynthetic mechanism and photoactive materials. Despite this significance, experimental elucidation of excited-state aromaticity is still unsolved, particularly for the excited singlet state. Here, as an unconventional approach, time-resolved IR (TRIR) spectroscopy on aromatic and anti-aromatic hexaphyrin congeners shed light on excited-singlet-state aromaticity. The contrasting spectral features between the Fourier transform IR and TRIR spectra reveal the aromaticity-driven structural changes, corroborating aromaticity reversal in the excited singlet states. Our paradigm for excited-state aromaticity, the correlation of IR spectral features with aromaticity reversal, provides another fundamental key to understanding the role of (anti)aromaticity in the stability, dynamics, and reactivity in the excited singlet state of π-conjugated molecular systems.

  • 49. Ohshita, Joji
    et al.
    Hatanaka, Yosuke
    Matsui, Shigenori
    Mizumo, Tomonobu
    Kunugi, Yoshihito
    Honsho, Yoshihito
    Saeki, Akinori
    Seki, Shu
    Tibbelin, Julius
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Takeuchi, Takae
    Effects of the silicon core structures on the hole mobility of star-shaped oligothiophenes2010In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 39, no 39, p. 9314-9320Article in journal (Refereed)
    Abstract [en]

    Star-shaped compounds with three or four oligothiophene units linked by an organosilicon core were prepared and their hole-transport capabilities were studied. A top-contact type thin film transistor (TFT) with a vapour-deposited film of tris[(ethylterthiophenyl)dimethylsilyl]methylsilane (3T(3)Si(4)) showed field-effect mobility (mu(FET)) of 4.4 x 10-5 cm(2) V-1 s(-1), while the device with the carbon centred analogue tris[(ethylterthiophenyl) dimethylsilyl] methane (3T(3)Si(3)C) showed no TFT activity. Intrinsic intramolecular hole mobility of 3T(3)Si(4) and 3T(3)Si(3)C was determined by time-resolved microwave conductivity measurements to be 8 x 10(-2) and 2 x 10(-2) cm(2) V-1 s(-1), respectively, arising from higher degree of s-p interaction in 3T(3)Si(4). To know more about the effects of the organosilicon core structures on the intermolecular hole mobility, we calculated internal reorganization energies for hole transfer at the (U) B3LYP/6-311+ G(d, p)//(U) B3LYP/6-31G(d) level, which suggested smoother intermolecular charge transfer in the silicon derivative than the carbon and germanium analogues. Star-shaped compounds with quarterthiophene units behave in a different manner from the terthiophene derivatives and tris[(ethylquarterthiophenyl) dimethylsilyl] methane (4T(3)Si(3)C) showed higher TFT mobility of mu(FET) = 1.2 10-3 cm(2) V-1 s(-1) than its silicon analogue (4T(3)Si(4): mu(FET) = 5.4 10(-4) cm(2) V-1 s(-1)). This is probably due to the more condensed packing of 4T3Si3C in the film, arising from the shorter Si-C bonding. Compounds with four terthiophene units were also prepared and tetrakis[(ethylterthiophenyl)dimethylsilyl] silane (3T(4)Si(5)) showed the mobility of mu(FET) = 2.0 x 10-4 cm(2) V-1 s(-1), higher than that of 3T(3)Si(4), indicating the potential of tetrakis(oligothiophenyl) compounds as the TFT materials. Tetrakis[(ethylterthiophenyl) dimethylsilyl] germane (3T(4)Si(4)Ge) was less thermally stable and could not be processed to a film by vapour-deposition, but was found to be TFT active in the spin-coated film, although the mobility was rather low (mu(FET) = 7.7 x 10(-7) cm(2) V-1 s(-1)).

  • 50. Ohshita, Joji
    et al.
    Kawamoto, Hiroyuki
    Kunai, Atsutaka
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Formation of Acylsilenolates from Bis(acyl)trisilanes as the Silicon Analogues of Acylenolates2010In: Organometallics, ISSN 0276-7333, E-ISSN 1520-6041, Vol. 29, no 18, p. 4199-4202Article in journal (Refereed)
    Abstract [en]

    Reactions of bis(acyl)trisilanes with tris(trimethylsilyl)silyllithium in THF, followed by treatment of the resulting dark red solutions with alkyl halides, gave the Si-alkylated products and tetrakis(trimethylsilyl)silane, indicating the formation of lithium acylsilenolates via Si-Li exchange. Exo-thermic formation of lithium acylsilenolate was demonstrated by DFT calculations on a model reaction.

12 1 - 50 of 77
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