Abstract
All-trans carotenoids have low-lying singlet states with different symmetries and the energy transfer from carotenoid to bacteriochlorophyll is governed by internal conversion and vibrational relaxation. According to theoretical calculation of Tavan and Schulten in shorter-chain carotenoids and our work (Furuichi et. al. 2002), the order of energy states of carotenoid are, from higher energy level, as 1Bu+, 3Ag-, 1Bu- and 2Ag- for the number of conjugated double bond n = 11-13. In the present investigation, we focus our attention on detection of those energy states. Especially detection of the 3Ag- states is rather difficult so we used 30 fs pulse duration and THF as a polar solvent. On the measurement, we could observe stimulated fluorescence from not only optically-active 1Bu+ but several low-lying hidden states in the initial stage. According to energy diagram, those stimulated fluorescence from low-lying states are concluded as 1Bu- and 3Ag-.
