Temperature dependence of the lowest excited singlet-state lifetime of all-t r a n s-β-carotene and fully deuterated all-t r a n s-β-carotene

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Abstract
A 4 ps, 450 nm laser pulse was used to electronically excite all‐trans‐β‐carotene and all‐trans‐β‐carotene‐d56 in 3‐methylpentane. The transient absorption spectra of these molecules were measured as a function of temperature down to 20 K. In all cases the 400–500 nm electronic absorption band of each carotene bleaches and a new absorption band near 560 nm appears immediately upon excitation. These bands recover with single exponential kinetics: τ=8.1±0.5 ps for all‐trans‐β‐carotene, and τ=10.5±0.6 ps for all‐trans‐β‐carotene‐d56 at 294 K. These recovery times increase by about a factor of 2 in glassy 3‐methylpentane, and are nearly independent of temperature from 100 to 20 K. The weak dependencies of the lowest excited single‐state lifetime of all‐trans‐β‐carotene on deuteration and temperature are discussed in terms of nonradiative decay mechanisms within carotenoids.