The Determination of the Internal Conversion of Carotenoids by Subpicosecond Time-resolved Raman Spectroscopy using Stimulated-Raman Process——the Correlation between the Lifetime and Energy Gap in each Excited State

Abstract

The internal conversion from 1B_u⁺ down to 2A_g^- facilitates the singlet energy transfer in the channel from 2A_g^- state of carotenoid to Q_y state of bacteriochlorophyll in antenna complex. In-between 1B_u⁺ and 2A_g^- state, spectroscopy such as resonance-Raman excitation profile found 1B_u^-, 3A_g^- state in the carotenoids having the conjugated double-bonding number, n = 9-13. This fact implies the sequential internal conversion from 1B_u⁺ take place through 3A_g^-, 1B_u^- states.
Spheroidene and lycopene were prepared by extraction, twice alumina column, and re-crystallization. They were measured with subpicosecond time-resolved Raman spectroscopy, which accomplished high temporal resolution with the use of two laser pulses for the probing of Raman process. The internal conversion processes of 1B_u⁺→3A_g^-→1B_u^-→2A_g^- were identified by a key stretching Raman line of each excited state. We are going to perform the singular-value decomposition and global fitting and to determine the lifetime of each excited state.