Abstract
By femtosecond ground-state recovery measurements the lifetime of the lowest excited singlet (S1) state in extra long carotenes, with 15 and 19 conjugated double bonds, has been determined to 850 and 470 fs, respectively. The nonradiative relaxation rates, due to internal conversion (kic), are interpreted together with the kic found for shorter carotenes homologous to trans-(beta) -carotene with 5, 7 and 11 ((beta) -carotene) conjugated double bonds. By using the energy gap law derived in the weak coupling limit the radiationless transitions were analyzed. The variations of kic depend mainly on the large variations in the coupling parameter, and the negative exponential energy gap dependence plays a minor role, due to the low value on the (gamma) parameter.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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