Primary processes in the photoisomerization of a nitrochromene studied by nanosecond laser photolysis - Kellmann, A.; Lindqvist, L.; Monti, S.; Tfibel, F.; Guglielmetti, R. (Elsevier)
The primary processes in the photoisomerization of 6-nitro-8-methoxy-2,2,3-trimethyl-2H-chromene (Chr) in toluene were studied from -3 to 55 ^oC by measuring the transient absorption changes produced by neodymium glass laser excitation at 353 nm (third harmonic) with a full width at half-maximum of 6 ns. The results indicate that the formation of a long-lived (about 50 s at 24 ^oC) coloured isomer (I) occurs owing to CO bond opening, partly directly from the excited singlet state of Chr and partly via the triplet state. A novel result is the observation that bond opening in triplet Chr leads to a cisoid isomer in the triplet state (^3X) which subsequently transforms into the coloured isomer. The lifetimes of ^3Chr and ^3X are about 80 ns and 450 ns respectively at 24 ^oC. The activation energies of the ^3Chr -〉 ^3X and ^3X -〉 O reactions are about 8 kcal mol^-^1 and about 10 kcal mol^-^1 respectively. The use of Chr as a model system for studies of spiropyran photochromism is discussed.
http://linkinghub.elsevier.com/retrieve/pii/0047-2670(83)80026-4
Keywords: V