Picosecond dynamics of singlet excited states of oxotetrahydrobenzo[c]phenanthridine in protic and aprotic solvents

Abstract

The spectral and kinetic properties of singlet excited states of two tetrahydrobenzo[c]phenanthridines—3,3-dimethyl-1,2,3,4-tetrahydrobenzo[c]phenanthridine-1-one (DTP) and 3,3-dimethyl-1,2,3,4-tetrahydrobenzo[c]phenanthridine-1-ol (DTP1)—are studied by picosecond absorption and luminescence spectroscopy in protic and aprotic solvents at 293 and 77 K. Based on the differences in the spectral and luminescent properties of DTP and DTP1, it was shown that the oxygen atom involved in the conjugation system of DTP is responsible for the formation of hydrogen-bonded complexes with alcohols. In the picosecond spectra of the induced absorption of DTP in n-hexane and acetonitrile, two bands peaked at 480 and 600 nm are observed, which are caused by the Tk ← T1-and Sn ← S1 absorption of DTP molecules solvated by the solvent by means of universal intermolecular interactions. In alcohols (methanol, ethanol, and n-propanol), an additional band is observed at 850 nm, which is caused by the Sm ← S1 absorption of hydrogen-bonded complexes. From analysis of the kinetics of the rise and decay of the induced absorption of DTP in n-hexane, acetonitrile, and alcohols, it is suggested that the main nonradiative channel in DTP is intersystem crossing.