Effect of the excitation wavelength and the structure of nitrated 1,2-dyhydroquinolines on dynamics of primary photophysical and photochemical processes

Abstract

Dynamics of transformations of excited states and active transient species generated in the photolysis of nitrated 1,2-dihydroquinolines (N-DHQ) has been studied by femto- and nanosecond laser pulse photolysis. Spectral and kinetic parameters of primary photophysical and photochemical processes have been determined, and their dependence on the substituent position at the aromatic ring of 1,2-dihydroquinoline (DHQ) and on the wavelength of excitation light has been established. The lifetime of the excited singlet state S1 in N-DHQ is ca. 100 and 500 fs for 8- and 6-nitro-substituted DHQ, respectively, which is shorter in comparison with DHQ without the nitro group by a factor of 104 and more. The major decay channel of the S1 state is the successive formation of three transient species with lifetimes of 0.5 to 16 ps. A triplet state is generated only upon excitation of the short-wavelength band by UV light. The quantum yield of the triplet state depends on the structure of N-DHQ.