HETEROGENEOUS HYDROGEN AND DEUTERIUM TRANSFER IN THE EXCITED-STATE OF2-METHYLBENZOPHENONE IN ETHER-PENTANE-ALCOHOL GLASSES AT 77 K

The phosphorescence decays of benzophenone, 2-methylbenzophenone (OMBP ), 3-methylbenzophenone, 4-methylbenzophenone (PMBP), and deuterated a nalogues of the ortho and para derivatives have been observed at 77 K in ether-pentane-alcohol glasses. The decays were fitted to gaussian d istributions of exponentials. An isotope effect on the decay is observ ed in the OMBP case, but not for PMBP. All decays, except those of the two OMBP derivatives, were well fitted to single-moded distributions of 5-6 ms with standard deviations of about 1 ms. The somewhat faster and markedly less homogeneous decay of the OMBP derivatives is attribu ted to internal hydrogen abstraction whose rate is dependent on the co nformation of the molecule and is competitive with radiative and other non-radiative decay pathways. Supporting this hypothesis is the obser vation of a fluorescence attributed to the appearance of the appropria te ortho-quinodimethane enol.