A new singlet-excited state of all-trans-spheroidene as detected by resonance-Raman excitation profiles

Measurements of resonance-Raman excitation profiles of the CC and C–C stretching Raman lines for crystalline all-trans-spheroidene in KBr disc at 77 K identified a new singlet state (17600 cm−1) that is located in-between the 2Ag− state (14200 cm−1) and the 1Bu+ state (19700 cm−1). The particular state is tentatively assigned to the 1Bu− state on the basis of the extrapolation of the PPP-MRD-CI calculations for the low-lying singlet states of shorter polyenes [P. Tavan, K. Schulten, J. Chem. Phys. 85 (1986) 6602], and its possible role in mediating the rapid 1Bu+ to 2Ag− internal conversion is discussed.