PHOTOHOMOLYSIS AND PHOTOIONIZATION OF SUBSTITUTED TETRAPHENYLETHANES AND C-C FRAGMENTATION OF 1,1,2,2-TETRA(P-R-PHENYL)ETHANE RADICAL CATIONS (R = H, CH3, OCH3, CL)

On photolysis of a series of tetraphenylethanes in 2,2,2-trifluoroetha nol (TFE) solution with 248 nm light, homolysis of the central C-C bon d occurs to yield the corresponding substituted diphenylmethyl radical s, in a process requiring one quantum of light. A second process takes place under conditions of high photon fluxes, namely biphotonic photo ionization to produce a radical cation, which subsequently undergoes e fficient C-C scission of the aliphatic central bond to yield the radic al and carbocation fragments. Photoionization and photohomolysis are t he preferred processes of excited state deactivation in the solvents a cetonitrile, TFE, and 1,1,1,3,3,3-hexafluoroisopropanol. The lifetime of the radical cation could be directly determined by following the fo rmation rates of the fragments in solution. The cations were character ized by their UV absorption spectra and electrophilic reactivities.