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

Low-temperature irradiations of 1-phenylcyclohexene (PC6) yield two singlet state 2 + 2 photodimers and two 4 + 2 cycloadducts. The 4 + 2 adducts are not observed in low intensity lamp irradiations at room temperature but are produced in significant quantities when PC6 solutions are subjected to higher intensity laser irradiation. The results indicate a reaction mechanism involving two trans-PC6 molecules. The findings are consistent with earlier kinetic observations that the decay of trans-PC6 adopts a significant second-order component at lower temperatures. The transient−transient reaction also occurs under triplet-sensitized low-temperature/low-intensity or room temperature/high-intensity irradiation conditions. Triplet-sensitized irradiations also yield significant 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 3PC6* to its ground state is in the range 0.28 to 4.0 × 105 L mol-1 s-1 consistent with t...