Protonation dependent electron transfer in 2-styrylquinolines

The absorption and emission spectra for 4′-substituted-2-trans-styrylquinoiline (X = NMe2, 1; H, 2; CN, 3; NO2, 4) and 4′-N,N-dimethylamino-2-trans-styrylnaphthalene 5 were studied in various solvents and at various acid concentrations. Monoprotonated or doubly protonated forms of 1 are present depending on the acid concentration. Excited state deprotonation of the doubly protonated form of 1 is observed in aprotic dichloromethane solvent. This excited state deprotonation process can be prevented by introducing protic methanol to the aprotic solvent media.