Photochemistry of the biradicals derived from the photodecomposition of 2,2,6,6-tetraphenylcyclohexanone

Laser photolysis of 2,2,6,6-tetraphenylcyclohexanone leads to biradical 2 following Norrish type I cleavage and decarbonylation. Excitation of 2 in one- or two-laser experiments leads to a new photoproduct, characterized as 9. Transient studies of the photochemistry of 2 reveal a very short lived excited state for the biradical (T - 2.5 ns in benzene at room temperature) which decays leading to one of the intermediates in the reaction path to 9. This intermediate absorbs strongly at 480 nm and has lifetimes of 0.9 and 1.1 ps in acetonitrile and benzene, respectively; this intermediate has been tentatively assigned structure 10, produced via cyclization at one of the biradical termini. The dramatic difference between the one- and two-photon photochemistry of 1 illustrates well the way in which laser chemistry can differ from photoprocesses initiated by conventional light sources.NRC publication: Ye