The Correlation of the Energy-Gap Law with Time Constants of Internal Conversion in Carotenoids Analyzed by Femtosecond Time-Resolved Absorption Spectroscopy

Abstract

Energy transfer from carotenoids to chlorophylls competes with internal conversion. Energy diagram of carotenoids has been determined by spectroscopic measurements, and these time constants may follow the energy-gap law. Target carotenoids are lycopene (n = 11), anhydrorhodovibrin (n = 12) and spirilloxanthin (n = 13). The order of internal conversion is expected as 1¹B_u⁺ → 3¹A_g⁻ → 1¹B_u⁻ → 2¹A_g⁻ → 1¹A_g⁻. Each time constant should depend on energy-gap of each step in internal conversion. Time-resolved absorption spectra of these three carotenoids show above four excited states. Spectral pattern and lifetime of each electronic state have determined by singular-value decomposition and global fitting. By the result, the relation with energy-gap law has been examined.