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Publications (10 of 17) Show all publications
Brumboiu, I. E., Ericsson, L. K. E., Blazinic, V., Hansson, R., Opitz, A., Brena, B. & Moons, E. (2022). Photooxidation of PC60BM: new insights from spectroscopy. Physical Chemistry, Chemical Physics - PCCP, 24(42), 25753-25766
Open this publication in new window or tab >>Photooxidation of PC60BM: new insights from spectroscopy
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2022 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 24, no 42, p. 25753-25766Article in journal (Refereed) Published
Abstract [en]

This joint experimental-theoretical spectroscopy study of the fullerene derivative PC60BM ([6,6]-phenyl-C-60-butyric acid methyl ester) aims to improve the understanding of the effect of photooxidation on its electronic structure. We have studied spin-coated thin films of PC60BM by X-ray Photoelectron Spectroscopy (XPS), Near-edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy, and Fourier Transform Infrared Spectroscopy (FTIR), before and after intentional exposure to simulated sunlight in air for different lengths of time. The pi* resonance in the C1s NEXAFS spectrum was found to be a very sensitive probe for the early changes to the fullerene cage, while FTIR spectra, in combination with O1s NEXAFS spectra, enabled the identification of the oxidation products. The changes observed in the spectra obtained by these complementary methods were compared with the corresponding Density Functional Theory (DFT) calculated single-molecule spectra of a large set of in silico generated oxidation products of PC60BM where oxygen atoms were attached to the C-60 cage. This comparison confirms that photooxidation of PC60BM disrupts the conjugation of the fullerene cage by a transition from sp(2) to sp(3)-hybridized carbon and causes the formation of several oxidation products, earlier proposed for C-60. The agreement between experimental and calculated IR spectra suggests moreover the presence of dicarbonyl and anhydride structures on the fullerene cage, in combination with cage opening at the adsorption site. By including PC60BM with physisorbed O-2 molecules on the cage in our theoretical description in order to model oxygen diffused through the film, the experimental O1s XPS and O1s NEXAFS spectra could be reproduced.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2022
National Category
Physical Chemistry Theoretical Chemistry
Identifiers
urn:nbn:se:uu:diva-494527 (URN)10.1039/d2cp03514f (DOI)000855867000001 ()36128981 (PubMedID)
Funder
Swedish Research Council, 2018-07152Swedish Research Council, 2015-03778Swedish Research Council, 2014-03776Vinnova, 2018-04969Swedish Research Council Formas, 2019-02496Knut and Alice Wallenberg Foundation, KAW-2016.0059Knut and Alice Wallenberg Foundation, KAW-2013.0020Göran Gustafsson Foundation for Research in Natural Sciences and MedicineCarl Tryggers foundation German Research Foundation (DFG), 239543752
Available from: 2023-01-18 Created: 2023-01-18 Last updated: 2023-01-18Bibliographically approved
Brumboiu, I. E., Haldar, S., Lüder, J., Eriksson, O., Herper, H. C., Brena, B. & Sanyal, B. (2019). Ligand effects on the linear response Hubbard U: The case of transition metal phthalocyanines. Journal of Physical Chemistry A, 123(14), 3214-3222
Open this publication in new window or tab >>Ligand effects on the linear response Hubbard U: The case of transition metal phthalocyanines
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2019 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 123, no 14, p. 3214-3222Article in journal (Refereed) Published
Abstract [en]

It is established that density functional theory (DFT) + U is a better choice compared to DFT for describing the correlated electron metal center in organometallics. The value of the Hubbard U parameter may be determined from linear response, either by considering the response of the metal site alone or by additionally considering the response of other sites in the compound. We analyze here in detail the influence of ligand shells of increasing size on the U parameter calculated from the linear response for five transition metal phthalocyanines. We show that the calculated multiple-site U is larger than the single-site U by as much as 1 eV and the ligand atoms that are mainly responsible for this difference are the isoindole nitrogen atoms directly bonded to the central metal atom. This suggests that a different U value may be required for computations of chemisorbed molecules compared to physisorbed and gas-phase cases.

National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:uu:diva-300117 (URN)10.1021/acs.jpca.8b11940 (DOI)000464768100011 ()30892039 (PubMedID)
Funder
Swedish Research Council, 2014-3776Swedish Research Council, 2016-05366Swedish Research Council, 2017-05447Knut and Alice Wallenberg Foundation, KAW-2013.0020Swedish National Infrastructure for Computing (SNIC)
Available from: 2016-08-02 Created: 2016-08-02 Last updated: 2019-05-15Bibliographically approved
Zhang, T., Brumboiu, I. E., Grazioli, C., Guarnaccio, A., Coreno, M., de Simone, M., . . . Puglia, C. (2018). Lone-Pair Delocalization Effects within Electron Donor Molecules: The Case of Triphenylamine and Its Thiophene-Analog. The Journal of Physical Chemistry C, 122(31), 17706-17717
Open this publication in new window or tab >>Lone-Pair Delocalization Effects within Electron Donor Molecules: The Case of Triphenylamine and Its Thiophene-Analog
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2018 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 31, p. 17706-17717Article in journal (Refereed) Published
Abstract [en]

Triphenylamine (TPA) and its thiophene-analog, N,N-diphenyl-2-thiophenamine (DPTA), are both well-known as electron-donating molecules implemented in optoelectronic devices such as organic solar cells and LEDs. Comprehensive valence and core level photoelectron spectroscopy, as well as near edge X-ray absorption spectroscopy (NEXAFS), measurements have been performed on gas phase TPA and DPTA. The experimental results have been compared to density functional theory calculations, providing a detailed description of the molecular electronic structure. Specifically, the C 1s photoelectron lines of both TPA and DPTA were resolved in the different C atom contributions and their binding energies explained as the result of two counter-acting effects: (1) the electronegativity of the nitrogen atom (and sulfur atom in DPTA) and (2) the the N (and S in DPTA) lone-pair electrons. In addition, the C K-edge NEXAFS spectrum of DPTA reveals that the lowest unoccupied molecular orbital (LUMO) energy position is affected differently if the core hole site is on the phenyl compared to the thiophene ring. The electron-donating properties of these two molecules are largely explained by the significant contribution of the N lone-pair electrons (p(z)) to the highest occupied molecular orbital. The contribution to the LUMO and to the empty density of states of the sulfur of the thiophene ring in DPTA explains the better performance of donor-pi-acceptor molecules containing this moiety and implemented in photoenergy conversion devices.

National Category
Physical Sciences Theoretical Chemistry Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-355118 (URN)10.1021/acs.jpcc.8b06475 (DOI)000441484600014 ()
Funder
Swedish Research Council, VR 2014-3776Carl Tryggers foundation
Note

Title in thesis list of papers: Lone Pair Delocalization Effect within Electron Donor Molecules:The Case of Triphenylamine (TPA) and Its Thiophene-Analog(DPTA)

Available from: 2018-06-29 Created: 2018-06-29 Last updated: 2018-10-15Bibliographically approved
Brumboiu, I. E., Haldar, S., Luder, J., Eriksson, O., Herper, H. C., Brena, B. & Sanyal, B. (2016). Influence of Electron Correlation on the Electronic Structure and Magnetism of Transition-Metal Phthalocyanines. Journal of Chemical Theory and Computation, 12(4), 1772-1785
Open this publication in new window or tab >>Influence of Electron Correlation on the Electronic Structure and Magnetism of Transition-Metal Phthalocyanines
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2016 (English)In: Journal of Chemical Theory and Computation, Vol. 12, no 4, p. 1772-1785Article in journal (Refereed) Published
Abstract [en]

There exists an extensive literature on the electronic structure of transition-metal phthalocyanines (TMPcs), either as single molecules or adsorbed on surfaces, where explicit intra-atomic Coulomb interactions of the strongly correlated orbitals are included in the form of a Hubbard U term. The choice of U is, to a large extent, based solely on previous values reported in the literature for similar systems. Here, we provide a systematic analysis of the influence of electron correlation on the electronic structure and magnetism of several TMPcs (MnPc, FePc, CoPc, NiPc, and CuPc). By comparing calculated results to valence-band photoelectron spectroscopy measurements, and by determining the Hubbard term from linear response, we show that the choice of U is not as straightforward and can be different for each different TMPc. This, in turn, highlights the importance of individually estimating the value of U for each system before performing any further analysis and shows how this value can influence the final results.

National Category
Physical Sciences Materials Chemistry Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-281097 (URN)10.1021/acs.jctc.6b00091 (DOI)000374196400034 ()26925803 (PubMedID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2016-03-17 Created: 2016-03-17 Last updated: 2017-01-25Bibliographically approved
Brumboiu, I. E. (2016). Molecules and Light: A Journey into the World of Theoretical Spectroscopy. (Doctoral dissertation). Uppsala: Acta Universitatis Upsaliensis
Open this publication in new window or tab >>Molecules and Light: A Journey into the World of Theoretical Spectroscopy
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Two of the main technological challenges of the century are the production of clean energy, on the one hand, and the development of new materials for electronic and spintronic applications that could increase the speed and the storage capacity of regular electronic devices, on the other hand. Organic materials, including fullerenes, organic polymers and organic molecules with metal centres are promising candidates for low-cost, flexible and clean technologies that can address these challenges. A thorough description of the electronic properties of such materials is, therefore, crucial. The interaction of electromagnetic radiation with the molecule can provide the needed insight into the electronic and vibrational levels and on possible chemical interactions. In order to explain and interpret experimentally measured spectra, a good theoretical description of the particular spectroscopy is necessary. Within density functional theory (DFT), the current thesis discusses the theoretical tools used to describe the spectroscopic properties of molecules with emphasis on two classes of organic materials for photovoltaics, molecular electronics and spintronics. Specifically, the stability of the fullerene derivative PC60BM is investigated in connection with its use as an electron acceptor in organic solar cells and the valence band electronic structure of several transition metal phthalocyanines is studied for their possible application in electronics and spintronics. The spectroscopies discussed in the current work are: the photoelectron spectroscopy of the valence band, X-ray photoelectron spectroscopy of the core levels, near-edge X-ray absorption fine structure, Infrared and Raman vibrational spectroscopies

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. p. 109
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1393
Keywords
Theoretical spectroscopy, XPS, NEXAFS, PCBM, Metal phthalocyanine, Organic solar cells
National Category
Natural Sciences
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-300123 (URN)978-91-554-9630-2 (ISBN)
Public defence
2016-09-16, Polhemsalen, Ångström, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2016-08-26 Created: 2016-08-02 Last updated: 2016-09-20
Bidermane, I., Brumboiu, I., Totani, R., Grazioli, C., Shariati Nilsson, M. N., Herper, H., . . . Puglia, C. (2015). Atomic Contributions to the Valence Band Photoelectron Spectra of Metal-free, Iron and Manganese Phthalocyanines. Journal of Electron Spectroscopy and Related Phenomena, 205, 92-97
Open this publication in new window or tab >>Atomic Contributions to the Valence Band Photoelectron Spectra of Metal-free, Iron and Manganese Phthalocyanines
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2015 (English)In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 205, p. 92-97Article, review/survey (Other academic) Published
Abstract [en]

The present work reports a photoelectron spectroscopy study of the low-energy region of the valence band of metal-free phthalocyanine (H2Pc) compared with those of iron phthalocyanine (FePc) and manganese phthalocyanine (MnPc). We have analysed in detail the atomic orbital composition of the valence band both experimentally, by making use of the variation in photoionization cross-sections with photon energy, and theoretically, by means of density functional theory. The atomic character of the Highest Occupied Molecular Orbital (HOMO), reflected on the outermost valence band binding energy region, is different for MnPc as compared to the other two molecules. The peaks related to the C 2p contributions, result in the HOMO for H2Pc and FePc and in the HOMO-1 for MnPc as described by the theoretical predictions, in very good agreement with the experimental results. The DFT simulations, discerning the atomic contribution to the density of states, indicate how the central metal atom interacts with the C and N atoms of the molecule, giving rise to different partial and total density of states for these three Pc molecules.

Keywords
Valence band; X-ray photoelectron spectroscopy; DFT; Phthalocyanines
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-217083 (URN)10.1016/j.elspec.2015.09.004 (DOI)000367282400011 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationCarl Tryggers foundation
Available from: 2014-01-29 Created: 2014-01-29 Last updated: 2017-12-06Bibliographically approved
Brumboiu, I. E., Ericsson, L., Hansson, R., Moons, E., Eriksson, O. & Brena, B. (2015). The influence of oxygen adsorption on the NEXAFS and core-level XPS spectra of the C-60 derivative PCBM. Journal of Chemical Physics, 142(5), Article ID 054306.
Open this publication in new window or tab >>The influence of oxygen adsorption on the NEXAFS and core-level XPS spectra of the C-60 derivative PCBM
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2015 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 142, no 5, article id 054306Article in journal (Refereed) Published
Abstract [en]

Fullerenes have been a main focus of scientific research since their discovery due to the interesting possible applications in various fields like organic photovoltaics (OPVs). In particular, the derivative [6,6]-phenyl-C-60-butyric acid methyl ester (PCBM) is currently one of the most popular choices due to its higher solubility in organic solvents compared to unsubstituted C-60. One of the central issues in the field of OPVs is device stability, since modules undergo deterioration (losses in efficiency, open circuit voltage, and short circuit current) during operation. In the case of fullerenes, several possibilities have been proposed, including dimerization, oxidation, and impurity related deterioration. We have studied by means of density functional theory the possibility of oxygen adsorption on the C-60 molecular moiety of PCBM. The aim is to provide guidelines for near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) measurements which can probe the presence of atomic or molecular oxygen on the fullerene cage. By analysing several configurations of PCBM with one or more adsorbed oxygen atoms, we show that a joint core level XPS and O1s NEXAFS investigation could be effectively used not only to confirm oxygen adsorption but also to pinpoint the bonding configuration and the nature of the adsorbate.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-248192 (URN)10.1063/1.4907012 (DOI)000349614200019 ()25662644 (PubMedID)
Available from: 2015-04-12 Created: 2015-03-30 Last updated: 2017-12-04Bibliographically approved
Brumboiu, I. E., Totani, R., de Simone, M., Coreno, M., Grazioli, C., Lozzi, L., . . . Brena, B. (2014). Elucidating the 3d Electronic Configuration in Manganese Phthalocyanine. Journal of Physical Chemistry A, 118(5), 927-932
Open this publication in new window or tab >>Elucidating the 3d Electronic Configuration in Manganese Phthalocyanine
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2014 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 118, no 5, p. 927-932Article in journal (Refereed) Published
Abstract [en]

To shed light on the metal 3d electronic structure of manganese phthalocyanine, so far controversial, we performed photoelectron measurements both in the gas phase and as thin film. With the purpose of explaining the experimental results, three different electronic configurations close in energy to one another were studied by means of density functional theory. The comparison between the calculated valence band density of states and the measured spectra revealed that in the gas phase the molecules exhibit a mixed electronic configuration, while in the thin film, manganese phthalocyanine finds itself in the theoretically computed ground state, namely, the b2g1eg3a1g1b1g0 electronic configuration.

Keywords
MnPc, photoelectron spectroscopy, density functional theory
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-218224 (URN)10.1021/jp4100747 (DOI)000331153400015 ()
Available from: 2014-02-10 Created: 2014-02-10 Last updated: 2017-12-06Bibliographically approved
Brumboiu, I. E. (2014). The Electronic Structure of Organic Molecular Materials: Theoretical and Spectroscopic Investigations. (Licentiate dissertation). Uppsala: Uppsala University, Department of Physics and Astronomy
Open this publication in new window or tab >>The Electronic Structure of Organic Molecular Materials: Theoretical and Spectroscopic Investigations
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In the present thesis the electronic properties of two organic molecules were studied by means of density functional theory (DFT) in connection to their possible applications in organic photovoltaics and molecular spintronics respectively.

The first analysed system is the C60 derivative PCBM extensively used in polymer solar cells for the charge separation process. Since fullerenes have been shown to undergo modifications as a result of light exposure, investigating their electronic structure is the first step in elucidating the photodegradation process. The electronic excitations from core levels to unoccupied molecular orbitals reveal not only the empty level structure of the molecule, but provide additional information related to the chemical bonds involving a specific atom type. In this way, they represent a means of determining the chemical changes that the molecule might withstand. The electronic transitions from carbon 1s core levels to unoccupied states are explained for the unmodified PCBM by a joint theoretical (DFT) and experimental study using the near edge x-ray absorption fine structure (NEXAFS) spectroscopy.

The second investigated system is the transition metal phthalocyanine with a manganese atom as the metal center. Manganese phthalocyanine (MnPc) is a single molecular magnet in which the spin switch process can be triggered by various methods. It has been shown, for instance, that the adsorption of hydrogen to the Mn center changes the spin state of the molecule from 3/2 to 1. More interestingly, the process is reversible and can be controlled, opening up the possibility of using MnPc as a quantum bit in magnetic memory devices. Up to this date, the d orbital occupation in MnPc has been under a long debate, both theoretical and experimental studies revealing different configurations. In this thesis the electronic structure of the phthalocyanine is thoroughly analysed by means of DFT and the calculated results are compared to photoelectron spectroscopy measurements. The combination of theoretical and experimental tools reveals that in gas phase at high temepratures the molecule exhibits a mixed electronic configuration. In this light, the possible control of the specific electronic state of the central metal represents an interesting prospect for molecular spintronics.

Place, publisher, year, edition, pages
Uppsala: Uppsala University, Department of Physics and Astronomy, 2014. p. 76
Keywords
materials theory, electronic structure, photoelectron spectroscopy, near-edge X-ray absorption fine structure
National Category
Atom and Molecular Physics and Optics Materials Chemistry Theoretical Chemistry Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics; Materials Science
Identifiers
urn:nbn:se:uu:diva-218225 (URN)
Presentation
2014-02-07, 2005, Uppsala, 14:00 (English)
Opponent
Supervisors
Available from: 2014-02-18 Created: 2014-02-10 Last updated: 2014-07-24Bibliographically approved
Bhandary, S., Brena, B., Panchmatia, P. M., Brumboiu, I., Bernien, M., Weis, C., . . . Sanyal, B. (2013). Manipulation of spin state of iron porphyrin by chemisorption on magnetic substrates. Physical Review B. Condensed Matter and Materials Physics, 88(2), 024401
Open this publication in new window or tab >>Manipulation of spin state of iron porphyrin by chemisorption on magnetic substrates
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2013 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 2, p. 024401-Article in journal (Refereed) Published
Abstract [en]

One of the key factors behind the rapid evolution of molecular spintronics is the efficient realization of spin manipulation of organic molecules with a magnetic center. The spin state of such molecules may depend crucially on the interaction with the substrate on which they are adsorbed. In this paper we demonstrate, using ab initio density functional calculations, that the stabilization of a high spin state of an iron porphyrin (FeP) molecule can be achieved via chemisorption on magnetic substrates of different species and orientations, viz., Co(001), Ni(001), Ni(110), and Ni(111). The signature of chemisorption of FeP on magnetic substrates is evident from broad features in N K x-ray absorption (XA) and Fe L-2,L-3 x-ray magnetic circular dichroism (XMCD) measurements. Our theoretical calculations show that the strong covalent interaction with the substrate increases Fe-N bond lengths in FeP and hence a switching to a high spin state (S = 2) from an intermediate spin state (S = 1) is achieved. Due to chemisorption, ferromagnetic exchange interaction is established through a direct exchange between Fe and substrate magnetic atoms as well as through an indirect exchange via the N atoms in FeP. The mechanism of exchange interaction is further analyzed by considering structural models constructed from ab initio calculations. Also, it is found that the exchange interaction between Fe in FeP and a Ni substrate is almost 4 times smaller than with a Co substrate. Finally, we illustrate the possibility of detecting a change in the molecular spin state by XMCD, Raman spectroscopy, and spin-polarized scanning tunneling microscopy.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-204271 (URN)10.1103/PhysRevB.88.024401 (DOI)000321123200001 ()
Available from: 2013-07-30 Created: 2013-07-29 Last updated: 2017-12-06Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-1671-8298

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