Spectral, Luminescent, and Photochemical Properties of 3-Styrybenzo[f]quinolines Substituted in the Styryl Moiety

Abstract

Spectral, luminescent, and photochemical properties of 3-styrylbenzo[f]quinoline derivatives with a methoxy group in the 2-position (2MSBQ) and a methoxymethylene group in the 4-position (4MMSBQ) of the styryl moiety have been investigated. Both compounds luminesce in the range of 380–480 nm and undergo reversible photoisomerization with quantum yields of 0.2–0.5. The side reaction of photocyclization of the cis-isomer is observed for 2MSBQ in addition to photoisomerization. Upon protonation, photocyclization is blocked and both compounds undergo only photoisomerization, with the quantum yields of photoisomerization increasing and those of fluorescence decreasing. The absorption and fluorescence spectra shift bathochromically. Geometry and electronic structure of the compounds were calculated with the use of DFT by a B3LYP/6-31G* method. By calculation using the TD-B3LYP/6-31G* method and the analysis of the transitions between molecular orbitals, the observed differences in the absorption spectra of 2MSBQ and 4MMSBQ have been explained. The comparison of the obtained results with the SBQ derivatives studied earlier shows several interesting substituent effects, which are explained in terms of the diabatic mechanism of photoisomerization.