Berlin 2008 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 9: POSTERS Single Molecules, Biopolymers, Membranes

CPP 9.11: Poster

Montag, 25. Februar 2008, 16:45–19:00, Poster A

A detailed theoretical analysis of the optical spectra of the prototype molecules tetracene and rubrene — •Taras Petrenko, Olga Krylova, Moritz Sokolowski, and Frank Neese — Institute for Physical and Theoretical Chemistry, Bonn University, Wegelerstrasse 12, 53115 Bonn, Germany,

Tetracene and rubrene are two prototype fluorescent molecules which are presently intensively studied. Interestingly, both molecules exhibit the same fluorescent backbone. However, due to electric repulsion between the phenyl groups, the backbone of rubrene is twisted, whereas it is planar for tetracene. Optical spectroscopy reveals that the S₀→S₁ transition in rubrene is redshifted with respect to tetracene by ∼2000 cm⁻¹ and that rubrene exhibits a considerably larger Stokes shift. In order to unravel the physical effect responsible for these differences we have performed normal coordinate analysis and frequency calculations using density functional theory in conjunction with linear response time-dependent density functional theory energy scan calculations. This yielded dimensionless normal coordinate displacements of the excited-state origin that were employed to calculate and fit the vibrational finestructure in absorption and fluorescence spectra. The analysis reveals that the ∼2000 cm⁻¹ red shift of 0-0 vibronic band of rubrene relative to tetracene is mainly caused by the inductive effect of the phenyl substituents that leads to destabilization of the donor MO. Funded by the DFG research unit 557 and the university of Bonn)