Measured Davydov splitting in oligothiophene crystals

CNR-INFM and Dipartimento di Scienza dei Materiali, Università di Milano Bicocca, Via Cozzi 53, I-20125 Milan, Italy.
The Journal of Chemical Physics (Impact Factor: 2.95). 06/2006; 124(19):194710. DOI: 10.1063/1.2196037
Source: PubMed


The polarized absorption spectra of single crystals of oligothiophenes in a wide spectral range are reported. The experimental procedure is discussed, underlying several details which are relevant to obtain reliable spectra particularly for samples of increasing thickness. On the basis of these considerations, it has been possible to fully detect the transition to the upper Davydov exciton originating from the first molecular state. The position and shape of the main exciton peak in these materials are compared and discussed, taking into consideration the molecular arrangement and the longitudinal contribution which depends on the transition moment orientation. The Davydov splitting values as deduced from the experimental data at room temperature are also reported either for the first vibronic replica or for the electronic transition as a whole. The difference between the purely transverse and the measured Davydov splitting is discussed.

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    • "r electronic transition . The ac polarized replicas in the spectral region between 2 . 7 and 3 . 6 eV are built on the lower b polarized excitonic band and obtain their oscillator strength through an intermolecular Herzberg – Teller coupling to the nearly free ac polarized exciton ( Silvestri et al . 2009 ; Spano 2003 , 2004 ; Spano et al . 2007 ; Tavazzi et al . 2006a ) . On the contrary , the b polarized exciton is very weakly allowed and it is more strongly coupled to phonons , showing a vibronic progression . On the basis of the calculations and the measurements in solution , other excitonic transitions are expected originating from the higher molecular electronic transitions ( Tavazzi et al . 201"

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