PHOTODIMERIZATION OF 1-PHENYLCYCLOHEXENE - A NOVEL TRANSIENT-TRANSIENT COMPONENT

Low-temperature irradiations of 1-phenylcyclohexene (PC6) yield two si nglet state 2 + 2 photodimers and two 4 + 2 cycloadducts. The 4 + 2 ad ducts are not observed in low intensity lamp irradiations at room temp erature but are produced in significant quantities when PC6 solutions are subjected to higher intensity laser irradiation. The results indic ate a reaction mechanism involving two trans-PC6 molecules, The findin gs are consistent with earlier kinetic observations that the decay of trans-PC6 adopts a significant second-order component at lower tempera tures, The transient-transient reaction also occurs under triplet-sens itized low-temperature/low-intensity or room temperature/high-intensit y irradiation conditions. Triplet-sensitized irradiations also yield s ignificant amounts of the 2 + 2 photodimers produced by attack of the PC6 triplet on its ground state, Quantum yield studies reveal that the rate of addition of (3)PC6 to it, ground state is in the range 0.28 to 4.0 x 10(5) L mol(-1) s(-1) consistent with the 1,2-biradical model for alkene triplet reactivity.