Electronic spectroscopy of lumiflavin in superfluid helium nanodroplets

We present the fluorescence excitation and dispersed emission spectra of lumiflavin doped into superfluid He nanodroplets. Both spectra show well resolved vibrational structure. The electronic origin transition at 21511 cm (1) is the strongest line in both spectra. Quantum chemical calculations with DFT and CASSCF methods support the assignment of S-1 to a pi pi* excited state. We obtain vibrational frequencies in the ground and lowest excited singlet state that can serve to test the validity of quantum chemical calculations. Multidimensional Franck-Condon factors are in good agreement with the intensities within the vibrational structure for S-0 and S-1. The strongest progression forming mode has a frequency of 164 cm (1) in both states and is assigned to an in-plane bending mode of the whole flavin chromophore with a large amplitude on the two methyl groups at ring I. (C) 2012 Elsevier B. V. All rights reserved.