Photoprocesses in 2-Benzylidene-5-(pyridin-4-ylmetylidene)cyclopentanone and Its Derivatives in Acetonitrile

The results of the study of the spectral, luminescent, and spectral–kinetic properties of 2-benzylidene-5-(pyridin-4-ylmethylidene)cyclopentanone and its diethylamino, methoxy, methylthio, and dimethoxy derivatives in acetonitrile at room temperature are presented. The introduction of electron-donating substituents leads to a bathochromic shift of the absorption maximum by 121 nm with respect to the maximum of the unsubstituted dienone and a bathochromic shift of the fluorescence maximum by 129 nm with respect to the maximum of the methoxy derivative. Upon laser irradiation of deoxygenated solutions of the dienones, intersystem crossing to the triplet state with a lifetime of 0.7–3.0 μs occurs, whereas for the methoxy, methylthio, and dimethoxy derivatives of the dienone, the formation of a stable photoproduct is observed.