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Updated: Jun 22, 2026

High Resolution Phonon-assisted Quasi-resonance Fluorescence Spectroscopy
Published on: June 28, 2016
Exciton-phonon coupling in molecular crystals: synergy between two intramolecular vibrational modes in
Leonardo Silvestri1, Silvia Tavazzi, Peter Spearman
1Dipartimento di Scienza dei Materiali, Università degli Studi di Milano Bicocca, via Cozzi 53, I-20125 Milano, Italy. leonardo.silvestri@mater.unimib.it
Abstract:
Exciton-phonon (EP) coupling in molecular crystals is investigated in the case where two intramolecular vibrational modes are involved and a theoretical model is presented which applies when one of the modes is strongly coupled to crystal excitons. The model is used to simulate the low energy portion of the absorption spectra of quaterthiophene (4T) single crystals, for which we find it appropriate to consider a low energy vibrational mode at 161 cm(-1) and an effective strongly coupled high energy mode at 1470 cm(-1). Our numerical results demonstrate that the high energy mode renormalizes the excitonic band, thereby strongly affecting the environment seen by the low energy mode and the overall EP coupling regime. Numerical simulations also confirm the existence of the new coupling regimes "intermediate-I" and "strong-I" already introduced for oligothiophene aggregates [Spano et al., J. Chem. Phys. 127, 184703 (2007)], which arise as a consequence of the large effective mass of low energy excitons in 4T crystals. Comparison with experimental high resolution absorption spectra is also reported and shown to support the model predictions.
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