Photophysical properties of solutions of 6,7-dimethoxy-3,4-dihydroisoquinoline

Abstract

The effect of acid-base interactions on the photophysical properties of 6,7-dimethoxy-3,4-dihydroisoquinoline in protic solvents is studied by the methods of steady-state and picosecond spectroscopy. It is found that the specific features of the spectral and luminescent properties of solutions of 6,7-dimethoxy-3,4-dihydroisoquinoline are connected with the presence of emission centers of two types—solvated initial molecules and their protonated cationic forms. Considerable long-wavelength shifts observed in the electronic absorption and fluorescence spectra of the cationic form of the molecule as compared to the spectra of its initial form are caused by the elongation of a conjugated chain present in the fragment of the molecule that separates the nitrogen atom and the oxygen atoms of the methoxy groups. The transition of the cationic form of the molecule to an excited electronic state is not accompanied by a change in its dipole moment.