Photochemical reactions of bifluorenylidene. Part 1.—Steady irradiation investigations

Abstract

On irradiation with light of wavelengths < 310 nm, solutions of bifluorenylidene in isopropanol are phototransformed, the reaction products being bifluorenyl and 2-hydroxypropylbifluorenyl. The proportion of the two compounds and the quantum yield of disappearance of bifluorenylidene depend on its concentration. It is shown that auto-inhibition of the reaction is as efficient as quenching by anthracene, and that bifluorenylidene phosphorescence is observed only after excitation at wavelengths < 310 nm. These facts suggest that the primary step of the reaction takes place in the triplet manifold and that the reactive triplet state is not the T₁ state. The quantum yield of disappearance of bifluorenylidene is an increasing linear function of the inverse of the square root of the intensity. A kinetic scheme which rationalizes these observations is proposed.