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Zietz, Burkhard
Publications (10 of 16) Show all publications
Marcellini, M., Nasedkin, A., Zietz, B., Petersson, J., Vincent, J., Palazzetti, F., . . . Davidsson, J. (2018). Transient isomers in the photodissociation of bromoiodomethane. Journal of Chemical Physics, 148(13), Article ID 134307.
Open this publication in new window or tab >>Transient isomers in the photodissociation of bromoiodomethane
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2018 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 148, no 13, article id 134307Article in journal (Refereed) Published
Abstract [en]

The photochemistry of halomethanes is fascinating for the complex cascade reactions toward either the parent or newly synthesized molecules. Here, we address the structural rearrangement of photodissociated CH2IBr in methanol and cyclohexane, probed by time-resolved X-ray scattering in liquid solution. Upon selective laser cleavage of the C-I bond, we follow the reaction cascade of the two geminate geometrical isomers, CH2I-Br and CH2Br-I. Both meta-stable isomers decay on different time scales, mediated by solvent interaction, toward the original parent molecule. We observe the internal rearrangement of CH2Br-I to CH2I-Br in cyclohexane by extending the time window up to 3 mu s. We track the photoproduct kinetics of CH2Br-I in methanol solution where only one isomer is observed. The effect of the polarity of solvent on the geminate recombination pathways is discussed.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2018
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-352489 (URN)10.1063/1.5005595 (DOI)000429359200029 ()29626862 (PubMedID)
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research
Available from: 2018-06-05 Created: 2018-06-05 Last updated: 2018-06-05Bibliographically approved
Pettersson-Rimgard, B., Föhlinger, J., Petersson, J., Lundberg, M., Zietz, B., Woys, A. M., . . . Hammarström, L. (2018). Ultrafast Interligand Electron Transfer in cis-[Ru(4,4’-dicarboxylate-2,2’-bipyridine)2(NCS)2]4- and Implications for Electron Injection Limitations in Dye Sensitized Solar Cells. Chemical Science, 9(41), 7958-7967
Open this publication in new window or tab >>Ultrafast Interligand Electron Transfer in cis-[Ru(4,4’-dicarboxylate-2,2’-bipyridine)2(NCS)2]4- and Implications for Electron Injection Limitations in Dye Sensitized Solar Cells
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2018 (English)In: Chemical Science, ISSN 2041-6520, Vol. 9, no 41, p. 7958-7967Article in journal (Refereed) Published
Abstract [en]

Interligand electron transfer (ILET) of the lowest metal-to-ligand charge transfer (MLCT) state of N712 (cis-[Ru(dcb)2(NCS)2]4−, where dcb = 4,4′-dicarboxylate-2,2′-bipyridine) in a deuterated acetonitrile solution has been studied by means of femtosecond transient absorption anisotropy in the mid-IR. Time-independent B3LYP density functional calculations were performed to assign vibrational bands and determine their respective transition dipole moments. The transient absorption spectral band at 1327 cm−1, assigned to a symmetric carboxylate stretch, showed significant anisotropy. A rapid anisotropy increase (τ1 ≈ 2 ps) was tentatively assigned to vibrational and solvent relaxation, considering the excess energy available after the excited singlet–triplet conversion. Thereafter, the anisotropy decayed to zero with a time constant τ2 ≈ 240 ps, which was assigned to the rotational correlation time of the complex in deuterated acetonitrile. No other distinctive changes to the anisotropy were observed and the amplitude of the slow component at time zero agrees well with that predicted for a random mixture of MLCT localization on either of the two dcb ligands. The results therefore suggest that MLCT randomization over the two dcb ligands occurs on the sub-ps time scale. This is much faster than proposed by previous reports on the related N3 complex [Benkö et al., J. Phys. Chem. B, 2004, 108, 2862, and Waterland et al., J. Phys. Chem. A, 2001, 105, 4019], but in agreement with that found by Wallin and co-workers [J. Phys. Chem. A, 2005, 109, 4697] for the [Ru(bpy)3]2+ (bpy = 2,2′-bipyridine) complex. This suggests that electron injection from the excited dye into TiO2 in dye-sensitized solar cells is not limited by ILET.

Place, publisher, year, edition, pages
RSC Publishing, 2018
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-357906 (URN)10.1039/C8SC00274F (DOI)000450897900004 ()30430000 (PubMedID)
Funder
Knut and Alice Wallenberg FoundationSwedish Energy Agency, 43599-1
Available from: 2018-08-21 Created: 2018-08-21 Last updated: 2019-01-18Bibliographically approved
Ayub, R., Papadakis, R., Jorner, K., Zietz, B. & Ottosson, H. (2017). Cyclopropyl Group: An Excited-State Aromaticity Indicator?. Chemistry - A European Journal, 23(55), 13684-13695
Open this publication in new window or tab >>Cyclopropyl Group: An Excited-State Aromaticity Indicator?
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2017 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 23, no 55, p. 13684-13695Article in journal (Refereed) Published
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.

National Category
Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-332141 (URN)10.1002/chem.201701404 (DOI)000412193700021 ()28683165 (PubMedID)
Funder
Wenner-Gren FoundationsSwedish Research Council, 2015-04538
Available from: 2017-10-24 Created: 2017-10-24 Last updated: 2018-04-23Bibliographically approved
Jorner, K., Dreos, A., Emanuelsson, R., El Bakouri, O., Fernández Galván, I., Borjesson, K., . . . Ottosson, H. (2017). Unraveling factors leading to efficient norbornadiene-quadricyclane molecular solar-thermal energy storage systems. Journal of Materials Chemistry A, 5(24), 12369-12378
Open this publication in new window or tab >>Unraveling factors leading to efficient norbornadiene-quadricyclane molecular solar-thermal energy storage systems
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2017 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 5, no 24, p. 12369-12378Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2017
National Category
Chemical Sciences Engineering and Technology Nano Technology
Research subject
Engineering Science with specialization in Nanotechnology and Functional Materials
Identifiers
urn:nbn:se:uu:diva-329636 (URN)10.1039/c7ta04259k (DOI)000403664800043 ()
Funder
Swedish Research Council, 2015-04538, 2011-04177, 2012-3910, 2016-03398Knut and Alice Wallenberg FoundationSwedish Foundation for Strategic Research Ragnar Söderbergs stiftelse
Available from: 2017-09-21 Created: 2017-09-21 Last updated: 2017-12-08Bibliographically approved
Freitag, M., Giordano, F., Yang, W., Pazoki, M., Hao, Y., Zietz, B., . . . Boschloo, G. (2016). Copper Phenanthroline as a Fast and High-Performance Redox Mediator for Dye-Sensitized Solar Cells. The Journal of Physical Chemistry C, 120(18), 9595-9603
Open this publication in new window or tab >>Copper Phenanthroline as a Fast and High-Performance Redox Mediator for Dye-Sensitized Solar Cells
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2016 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 18, p. 9595-9603Article in journal (Refereed) Published
Abstract [en]

The most commonly used redox mediators in dye-sensitized solar cells (DSCs), iodide/triiodide and cobalt trisbipyridine ([Co(bpy)(3)](2+/3+)), were successfully replaced by bis (2,9-dimethy1-1,10-phenanthroline) copp er (I/H) ([Cu(dmp)(2)](1+/2+)). The use of the copper complex based electrolyte led to an exceptionally high photovoltaic performance of 8.3% for LEG4-sensitized TiO2 solar cells, with a remarkably high open-circuit potential of above 1.0 V at 1000 W m(-2) under AM1.5G conditions. The copper complex based redox electrolyte has higher diffusion coefficients and is considerably faster in dye regeneration than comparable cobalt trisbipyridine based electrolytes. A driving force for dye regeneration of only 0.2 eV is sufficient to obtain unit yield, pointing to new possibilities for improvement in DSC efficiencies. The interaction of the excited dye with components of the electrolyte was monitored using steady-state emission measurements and time-correlated single-photon counting (TC-SPC). Our results indicate bimolecular reductive quenching of the excited LEG4 dye by the [Cu(dmp)(2)](2+) complex through a dynamic mechanism. Excited-state dye molecules can readily undergo bimolecular electron transfer with a suitable donor molecule. In DSCs this process can occur when the excited dye is unable to inject electrons into the TiO2. With a high electrolyte concentration the excited dye can be intercepted with an electron from the electrolyte resulting in the reduced state of the dye. Quenching of the reduced dye by the electrolyte competes with electron injection and results in a lower photocurrent. Quenching of excited LEG4 by complexes of [Cu(dmp)(2)](+), [Co(bpy)(3)](2+), and [Co(bpy)(3)](3+) followed a static mechanism, due ground-state dye-quencher binding. Inhibition of unwanted quenching processes by structural modifications may open ways to further increase the overall efficiency.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-298095 (URN)10.1021/acs.jpcc.6b01658 (DOI)000375969000007 ()
Funder
Swedish Energy AgencySwedish Research CouncilStandUp
Available from: 2016-06-29 Created: 2016-06-29 Last updated: 2017-11-28Bibliographically approved
El-Zohry, A. M., Cong, J., Karlsson, M., Kloo, L. & Zietz, B. (2016). Ferrocene as a rapid charge regenerator in dye-sensitized solar cells. Dyes and pigments, 132, 360-368
Open this publication in new window or tab >>Ferrocene as a rapid charge regenerator in dye-sensitized solar cells
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2016 (English)In: Dyes and pigments, ISSN 0143-7208, E-ISSN 1873-3743, Vol. 132, p. 360-368Article in journal (Refereed) Published
Abstract [en]

Using the reductive power of the ferrocene moiety (Fc), an ultrafast regeneration step via a covalent attachment of a Fc moiety to an organic triphenylamine-based dye (L1) when adsorbed on TiO2 is highlighted. Two modified dyes with one and two Fc moieties attached (L1Fc, and L1Fc2), respectively, were synthesized by addition to the L1 dye. These dyes have been studied spectroscopically using ultrafast transient absorption spectroscopy in the visible and the infrared (IR) regions. In acetonitrile, the results show an ultrafast excited state quenching of the modified dyes due to an expected electron transfer process from the Fc(s) to L1. Adsorbed onto TiO2, an electron transfer process is also detected from Fc to the oxidized dye (L1(+)). Despite the occurrence of an ultrafast regeneration step, the solar cell performance does not improve by the attachment of Fc(s) to the dye L1. Transient absorption measurements in the IR region revealed a fast electron recombination process to the Fc(+) moiety on an average time scale of ca. 300 ps, outcompeting the >12 ns process to L1(+). The reasons for the observed considerably faster recombination rate to Fc(+) than to L1(+) are discussed in detail. This study provides deep spectroscopic insights for such organic dyes utilized to afford ultrafast regeneration step without showing high performance in photovoltaic devices. In addition, this study will improve our understandings for the triangular relationship between the molecular design, electron kinetics, and the performance in photovoltaic devices.

Keywords
Electron dynamics, Charge transfer, Recombination, Transient absorption, Organic dyes
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-299825 (URN)10.1016/j.dyepig.2016.05.021 (DOI)000378456200043 ()
Funder
Swedish Research CouncilSwedish Energy AgencyKnut and Alice Wallenberg Foundation
Available from: 2016-07-29 Created: 2016-07-28 Last updated: 2017-11-28Bibliographically approved
Park, B.-w., Philippe, B., Jain, S. M., Zhang, X., Edvinsson, T., Rensmo, H., . . . Boschloo, G. (2015). Chemical engineering of methylammonium lead iodide/bromide perovskites: tuning of opto-electronic properties and photovoltaic performance. Journal of Materials Chemistry A, 3(43), 21760-21771
Open this publication in new window or tab >>Chemical engineering of methylammonium lead iodide/bromide perovskites: tuning of opto-electronic properties and photovoltaic performance
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2015 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 3, no 43, p. 21760-21771Article in journal (Refereed) Published
Abstract [en]

Hybrid (organic-inorganic) lead trihalide perovskites have attracted much attention in recent years due to their exceptionally promising potential for application in solar cells. Here a controlled one-step method is presented where PbCl2 is combined with three equivalents methylammonium halide (MAX, with X = land/or Br) in polar solvents to form MAPb(I-xBr(x))(3) perovskite films upon annealing in air at 145 degrees C. The procedure allows for a linear increment of the semiconductor bandgap from 1.60 eV to 2.33 eV by increasing the Br content. A transition from a tetragonal to a cubic structure is found when the Br fraction is larger than 0.3. X-ray photoelectron spectroscopy investigations shows that the increase of Br content is accompanied by a shift of the valence band edge to lower energy. Simultaneously, the conduction band moves to higher energy, but this shift is less pronounced. Time-resolved single-photon counting experiments of the perovskite materials on mesoporous TiO2 show faster decay kinetics for Br containing perovskites, indicative of improved electron injection into TiO2. Interestingly, kinetics of MAPb(12.7)Br(0.30)Cl(y) on TiO2 scaffold became faster after prolonged excitation during the measurement. In solar cell devices, MAPb(12.7)Br(0.30)), yielded best performance, giving more than 14% power conversion efficiency when used in combination with an n-type contact consisting of fluorine-doped tinoxide glass coated with dense TiO2 and a mesoporous Al2O3 scaffold, and a p-type contact, spiro-MeOTAD/Ag.

National Category
Physical Chemistry Materials Chemistry Materials Engineering
Identifiers
urn:nbn:se:uu:diva-268726 (URN)10.1039/c5ta05470b (DOI)000364020400042 ()
Funder
Swedish Energy AgencyStandUpSwedish Research CouncilGöran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of TechnologyKnut and Alice Wallenberg Foundation
Available from: 2015-12-09 Created: 2015-12-09 Last updated: 2017-12-01Bibliographically approved
Parada, G. A., Markle, T. F., Glover, S. D., Hammarström, L., Ott, S. & Zietz, B. (2015). Control over Excited State Intramolecular Proton Transfer and Photoinduced Tautomerization: Influence of the Hydrogen-Bond Geometry. Chemistry - A European Journal, 21(17), 6362-6366
Open this publication in new window or tab >>Control over Excited State Intramolecular Proton Transfer and Photoinduced Tautomerization: Influence of the Hydrogen-Bond Geometry
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2015 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 21, no 17, p. 6362-6366Article in journal (Refereed) Published
Abstract [en]

The influence of H-bond geometry on thedynamics of excited state intramolecular proton transfer(ESIPT) and photoinduced tautomerization in a series ofphenol-quinoline compounds is investigated. Control overthe proton donor–acceptor distance (dDA) and dihedralangle between the proton donor–acceptor subunits isachieved by introducing methylene backbone straps ofincreasing lengths to link the phenol and quinoline. Wedemonstrate that a long dDA correlates with a higher barrierfor ESIPT, while a large dihedral angle opens highlyefficient deactivation channels after ESIPT, preventing theformation of the fully relaxed tautomer photoproduct.

Keywords
excited state, fluorescence, hydrogen bonds, intramolecular proton transfer, phenols, tautomerism
National Category
Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-251468 (URN)10.1002/chem.201500244 (DOI)000352796100008 ()
Available from: 2015-04-19 Created: 2015-04-19 Last updated: 2017-12-04Bibliographically approved
Unger, E. L., Yang, L., Zietz, B. & Boschloo, G. (2015). Hole transporting dye as light harvesting antenna in dye-sensitized TiO2 hybrid solar cells. JOURNAL OF PHOTONICS FOR ENERGY, 5, Article ID 057406.
Open this publication in new window or tab >>Hole transporting dye as light harvesting antenna in dye-sensitized TiO2 hybrid solar cells
2015 (English)In: JOURNAL OF PHOTONICS FOR ENERGY, ISSN 1947-7988, Vol. 5, article id 057406Article in journal (Refereed) Published
Abstract [en]

We herein demonstrate the viability of utilizing the hole transporting medium of solid-state dye-sensitized solar cells for light harvesting. When using a hole transporting dye (HTD) in addition to an interface dye (ID) bound to the surface of the mesoporous metal oxide scaffold, both are shown to contribute to the photocurrent. Efficient energy transfer (ET) from the HTD to the ID was accomplished by spectrally matching two triphenylamine dyes. The photoluminescence of the HTD was found to be quenched in the presence of the ID. In nanosecond transient absorption measurements, rapid formation of the oxidized HTD was observed after photoexcitation of the ID, demonstrating fast regeneration of the oxidized ID by the HTD. In solar cell devices comprising both the ID and HTD, the spectral response of the external quantum efficiency shows that both dyes contribute to the photocurrent, resulting in a doubling of the photocurrent. In comparison with devices comprising only TiO2 and the HTD, devices with the additional ID exhibited an increased photovoltage due to more efficient charge-carrier separation and energy transfer. Combining and matching HTDs with IDs for optimal ID regeneration but also providing ET is thus a viable means to optimize hybrid solar cells based on mesoporous TiO2.

Keywords
solid-state dye-sensitized solar cell, hole transporting dye, energy transfer, regeneration
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-252715 (URN)10.1117/1.JPE.5.057406 (DOI)000352845700001 ()
Available from: 2015-05-11 Created: 2015-05-11 Last updated: 2015-05-11Bibliographically approved
El-Zohry, A. M., Roca-Sanjuán, D. & Zietz, B. (2015). Ultrafast Twisting of the Indoline Donor Unit Utilized in Solar Cell Dyes: Experimental and Theoretical Studies. The Journal of Physical Chemistry C, 119(5), 2249-2259
Open this publication in new window or tab >>Ultrafast Twisting of the Indoline Donor Unit Utilized in Solar Cell Dyes: Experimental and Theoretical Studies
2015 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 5, p. 2249-2259Article in journal (Refereed) Published
Abstract [en]

Previous time-resolved measurements on D149, the most-studied dye of the indoline family, had shown a fast time-component of 20–40 ps that had tentatively been attributed to structural relaxation. Using femtosecond transient absorption, we have investigated the isolated indoline donor unit (i.e., without acceptor group) and found an ultrafast decay characterized by two lifetimes of 3.5 and 23 ps. Density functional theory calculations show π-bonding and π*-antibonding character of the central ethylene group for the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO), respectively. The LUMO is localized on the flexible vinyl-diphenyl region of the donor unit and a twisting process is assumed to occur as a deactivation process for the excited molecule. This is confirmed by multireference second-order perturbation theory (CASSCF/CASPT2) calculations of the lowest-lying excited state, in which it is shown that torsion of the ethylene bond to 96° and pyramidalization to ca. 100° lead to a conical intersection with the ground state. Embedded in a plastic matrix, where double bond rotation is hindered, the decay is slowed down to nanoseconds. We have also investigated the dyes D102, D131, and D149, possessing the same indoline donor unit, by femtosecond transient absorption and found a similar decay component. The ca. 20 ps deactivation channel in D-family dyes is thus attributed to a twisting process of the donor unit. The fluorescence quantum yields of this unit and D149 were measured, and from comparison, the competition of the discovered twisting deactivation channel to the radiative decay of the excited indoline dyes could be confirmed. Blocking this deactivation channel is expected to further increase efficiency for the indoline dyes.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-263141 (URN)10.1021/jp505649s (DOI)
Available from: 2015-09-27 Created: 2015-09-27 Last updated: 2017-12-01Bibliographically approved
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