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The Electronic Structure of Organic Molecular Materials: Theoretical and Spectroscopic Investigations
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. (Materials Theory)
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. , 76 p.
Keyword [en]
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
URN: urn:nbn:se:uu:diva-218225OAI: diva2:695108
2014-02-07, 2005, Uppsala, 14:00 (English)
Available from: 2014-02-18 Created: 2014-02-10 Last updated: 2014-07-24Bibliographically approved
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
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.

MnPc, photoelectron spectroscopy, density functional theory
National Category
Atom and Molecular Physics and Optics
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

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