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Molecules and Light: A Journey into the World of Theoretical Spectroscopy
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. (Materials Theory)ORCID iD: 0000-0003-1671-8298
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. , 109 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1393
Keyword [en]
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: urn:nbn:se:uu:diva-300123ISBN: 978-91-554-9630-2OAI: oai:DiVA.org:uu-300123DiVA: diva2:950840
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
List of papers
1. Near-edge X-ray absorption fine structure study of the C-60-derivative PCBM
Open this publication in new window or tab >>Near-edge X-ray absorption fine structure study of the C-60-derivative PCBM
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2013 (English)In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 568, 130-134 p.Article in journal (Refereed) Published
Abstract [en]

The fullerene derivative [6,6]-phenyl-C-61-butyric acid methyl ester plays a key role for electron transport in polymer solar cells. We have studied the unoccupied molecular orbitals of PCBM by near edge X-ray absorption fine structure spectroscopy and were able to assign the main resonances to molecular moieties by comparison with calculated sum spectra of individual carbons. We analyzed specifically the origin of the high-energy shoulder to the first pi*-resonance and identified contributions from the lowest-energy transition of a specific carbon in the phenyl and from transitions to higher unoccupied orbitals of the unmodified carbons in the C-60-cage. 

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-201237 (URN)10.1016/j.cplett.2013.03.031 (DOI)000318320300025 ()
Available from: 2013-06-10 Created: 2013-06-10 Last updated: 2016-09-05Bibliographically approved
2. Elucidating the 3d Electronic Configuration in Manganese Phthalocyanine
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, 927-932 p.Article 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.

Keyword
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: 2016-09-05Bibliographically approved
3. The influence of oxygen adsorption on the NEXAFS and core-level XPS spectra of the C-60 derivative PCBM
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, 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: 2016-09-05Bibliographically approved
4. Atomic Contributions to the Valence Band Photoelectron Spectra of Metal-free, Iron and Manganese Phthalocyanines
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, 92-97 p.Article, 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.

Keyword
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: 2016-09-05Bibliographically approved
5. Influence of Electron Correlation on the Electronic Structure and Magnetism of Transition-Metal Phthalocyanines
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, 1772-1785 p.Article 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: 2016-09-05Bibliographically approved
6. Ligand effects on the linear response Hubbard U: The case of transition metal phthalocyanines
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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(English)Manuscript (preprint) (Other academic)
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-300117 (URN)
Available from: 2016-08-02 Created: 2016-08-02 Last updated: 2016-09-05
7. The valence band electronic structure of cobalt phthalocyanine from optimally tuned range-separated hybrid functionals
Open this publication in new window or tab >>The valence band electronic structure of cobalt phthalocyanine from optimally tuned range-separated hybrid functionals
(English)Manuscript (preprint) (Other academic)
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-300118 (URN)
Available from: 2016-08-02 Created: 2016-08-02 Last updated: 2016-09-05
8. Photon and binding energy dependent valence band photoelectron spectroscopy of organic molecules
Open this publication in new window or tab >>Photon and binding energy dependent valence band photoelectron spectroscopy of organic molecules
(English)Manuscript (preprint) (Other academic)
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-300119 (URN)
Available from: 2016-08-02 Created: 2016-08-02 Last updated: 2016-09-05
9. C1s NEXAFS investigations of PC60BM exposed to oxygen: a novel approach for the comparison of computed and experimental spectra
Open this publication in new window or tab >>C1s NEXAFS investigations of PC60BM exposed to oxygen: a novel approach for the comparison of computed and experimental spectra
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(English)Manuscript (preprint) (Other academic)
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-300121 (URN)
Available from: 2016-08-02 Created: 2016-08-02 Last updated: 2016-09-05
10. Spectroscopy of photo-oxidized PC60BM
Open this publication in new window or tab >>Spectroscopy of photo-oxidized PC60BM
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(English)Manuscript (preprint) (Other academic)
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-300122 (URN)
Available from: 2016-08-02 Created: 2016-08-02 Last updated: 2016-09-05

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