SOLVENT-DEPENDENT BEHAVIOR OF PHENANTHRENE-AMINE INTRAMOLECULAR EXCIPLEXES

The solvent dependence of the photophysical and photochemical behavior of several ((N,N-dimethylamino)alkyl)phenanthrenes in which the amino group is attached to the phenanthrene at C-9 or C-1 via a short polymethylene chain has been investigated. Intramolecular exciplex fluorescence is observed in moderately polar solvents but not in nonpolar solvents. The solvent dependence of exciplex fluorescence is attributed to exergonic formation of solvated exciplexes with loose geometries in polar solvents and endergonic exciplex formation in nonpolar solvents. in the case of the (aminoethyl)phenanthrene exciplex fluorescence is observed in highly polar solvents, including dimethylformamide, dimethyl sulfoxide, and acetonitrile-water binary mixtures and in frozen polar glasses. In the case of the (aminomethyl)phenanthrene moderately efficient photodeamination to yield 9-methylphenanthrene and 1,2-di-9-phenanthrylethane is observed. The solvent and temperature dependence of the kinetics of exciplex formation and decay are discussed and compared to results for other intramolecular arene-amine exciplexes.