Singlet internal conversion processes in the order of in all-trans-spheroidene and lycopene as revealed by subpicosecond time-resolved Raman spectroscopy

Key Raman lines ascribable to the 1 B u + , 3 A g - , 1 B u - and 2 A g - states were identified in the subpicosecond time-resolved Raman spectra of spheroidene and lycopene having 10 and 11 conjugated double bonds, respectively. The sequential rise-and-decay of the key Raman lines showed the internal conversion processes of 1 B u + → 3 A g - → 1 B u - → 2 A g - → 1 A g - (ground). The time constant in each step of internal conversion reflects the energy gap between the relevant states that had been determined by measurement of resonance – Raman excitation profiles [K. Furuichi, T. Sashima, Y. Koyama, Chem. Phys. Lett. 356 (2002) 547].