Photochemistry and Photophysics of (1-Naphthoyl)diphenylphosphine Oxide

Abstract

(1-Naphthoyl)diphenylphosphine oxide (1) was synthesized and characterized and its photochemistry investigated using emission spectroscopy, pulse radiolysis, and nanosecond laser flash photolysis. Fluorescence quantum yields are low in aprotic polar and nonpolar solvents. In methanol, as a result of hydrogen-bonding, change of S1 from an n,π* state to a π,π* state leads to the decrease in the rate constant for intersystem crossing and results, finally, in an increase in fluorescence. Preferential solvation was evaluated using the ET indicator “Reichardt's dye” (RD). ETN values were determined by gradually increasing the concentrations of methanol in methanol/acetonitrile mixtures. Fluorescence quantum yields correlate with the ETN values. Photolysis of 1 yields diphenyl[1-naphthoyl)oxy]phosphine (6), formed mainly via cage recombination of radicals. No radicals were detected by either nanosecond laser flash photolysis or pulse radiolysis of 1 in aprotic solvents. However, photolysis in methanol yields rad...