Determination of the photochemical efficiency of o-quinodimethane ring closure in room-temperature solutions by using time-delayed, two-color photolysis technique

Photochemical efficiency of o-quinodimethane (3) ring closure at room tempe rature was determined by using a time-delayed, two-color photolysis techniq ue. o-Quinodimethane (3) was generated by the photolysis of 1,2-bis[(phenyl seleno)methyl]benzene (1) by a KrF (248 nm) laser pulse and thus-generated 3 was photolyzed by a subsequent XeCl (308 nm)/XeF (351 nm) laser pulse wit h varying delay time of 0 to 3 s. The time profile of 3 was monitored by th e chemical analyses of benzocyclobutene (5) (a photochemical product of 3), which was formed by a one-photon process, and the spiro dimer of 3.(4) (a thermal product of 3) in the two-color photolysis experiments. The time pro file of 3 followed a second-order decay kinetics. The photochemical efficie ncy was obtained by the analysis of the delay-time dependence of the produc t yields; those of the consumption of 3 and the conversion 3 --> 5 by a sin gle pulse of the excimer laser were 81% and 5.7% for the XeCl laser, and 73 % and 2.3% for the XeF laser. This difference was attributed to the differe nt excited states involved in the photolysis. In contrast to the photolysis of 3 in argon or rigid organic matrixes, it was revealed that photochemica l conversion 3 --> 5 was not the main path in the solutions, and intermolec ular reactions predominated.