Surface photochemistry: Semiconductor mediated reactions of some saturated strained hydrocarbons

Quadricyclane (1) and 1,8-bishoniocubane (2) have been found to undergo valence isomerization to norborndiene and tricyclo[4.2.2.02,5]deca-3,7-diene, respectively, on illuminated CdS and ZnO. An electron transfer mechanism is proposed. Quantum yield, solvent effects, the role of oxygen, and the quenching of the reaction were investigated, and were consistent with this interpretation. The thermal reaction of 1 on CdS was also suggested to be an electron transfer process involving, in this case, defects or trapped holes on the surface of the semiconductor. An examination of a series of strained hydrocarbons structurally related to 1 (tetracyclo[3.3.0.02,8.04,6]octane 3, pentacyclo[4.3.0.02,4.03.805,7]nonane 4 and pentacyclo[4.4.0.02,4.03,8.05,7]decane 5) resulted, largely, in a demonstration of the resistance of their respective radical cations to rearrangement prior to back electron transfer. Calculations by MNDO, in combination with a modified version of MM2, were used to explore the differences in the re...