Ph.D. thesis, Abstract and download information

M. Hoffmann,
Frenkel- and Charge-Transfer Excitons in Quasi-One-Dimensional
Molecular Crystals with Strong Intermolecular Orbital Overlap,
Ph.D. thesis, TU Dresden, Dresden 2000.

Abstract:

We present a theoretical and experimental study on the lowest electronically excited states in quasi-one-dimensional molecular crystals. The specific calculations and the experiments are performed for the model compounds MePTCDI (N-N'-dimethylperylene-3,4:9,10-dicarboximide) and PTCDA (3,4:9,10-perylenetetracarboxylic dianhydride). The intermolecular interactions between nearest neighbors are quantum chemically analyzed on the basis of semi-empirical (ZINDO/S) Hartree-Fock calculations and a singly excited configuration interaction scheme. Supermolecular dimer states are projected onto a basis set of localized excitations. The nature of the lowest states is then completely explained as a superposition of molecular and low lying charge-transfer excitations. The CT excitations show a significant intrinsic transition dipole, which is oriented approximately parallel to the molecular planes and has a large component along the molecular M-axis. The exciton states in the one-dimensional stacks are described by a model Hamiltonian that includes interactions between three vibronic levels of the lowest molecular excitation and nearest-neighbor CT excitations. The three-dimensional crystal structure is considered by Frenkel exciton transfer between arbitrary molecules. This model is compared to polarized absorption spectra. With a small set of parameters, we can describe the key features of the absorption spectra, the polarization behavior, and the Davydov splitting. The variation of the polarization ratio for the various exciton states is analyzed as a direct qualitative proof for the mixing between Frenkel and charge-transfer excitons.

Keywords:

Frenkel excitons; charge-transfer excitons; polarized absorption; organic crystals; thin films;
MePTCDI; N-N'-dimethylperylene-3,4:9,10-dicarboximide;
PTCDA; 3,4:9,10-perylenetetracarboxylic dianhydride

Available download formats:

This thesis is a scientific publication and should be treated and referenced accordingly. There are no further copyright restrictions.

I strongly recommend to use the ps versions. The pdf files were created only by subsequent transformation. In the result, the pdf files are printable but are slow and difficult to read with Acroread.

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Double-sided printing on A4 paper (210mm x 297mm) DissMH2A.ps DissMH2A.pdf
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last updated: 16 Apr 2001 (4 Nov 2003: damaged file DissMH2A.ps replaced by working version)