The excitonic splitting and its interplay with vibronic coupling in H-bonded molecular dimers is examined in a joint theoretical and experimental investigation. Three representative examples are selected for which high-resolution resonant two-photon ionization spectra have been recorded. The theoretical analysis relies on the CC2/aug-cc-pVTZ electronic structure method for the pertinent potential energy surfaces and a suitable vibronic model to determine the spectral intensity distribution. Important features of the experimental recordings can be reproduced and interpreted in this way, although deviations remain. As the most prominent aspect, the vertical electronic Davydov splitting exceeds the observed vibronic excitonic splitting by a factor of 10-40. This discrepancy can be reconciled by considering the quenching of the excitonic splitting by the excitation of vibrational modes in the electronic transition. Two different ways of treating this quenching theoretically are compared, and the consequences for the temporal behaviour of the excitation energy transfer are explored.

Vibronic coupling and quenching of excitonic energy splittings in H-bonded molecular dimers

244th National Meeting (2012)

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