Kinetics of Photoreactive 4,4'-Dimethylbenzophenone Nanocrystals: Relative Contributions to Triplet Decay from Intermolecular H-Atom Transfer and Reductive Charge Transfer Quenching.

Crystals of 4,4'-dimethylbenzophenone ( DMBP ) are known to react by intermolecular H atom transfer, followed by radical pair recombination. To determine the contribution of the H atom transfer reaction to the deactivation of the triplet ketone, transient absorption spectra and kinetics were obtained using aqueous nanocrystalline suspensions. Single-exponential lifetimes of ca. 1185 ns with no deuterium isotope effect and inefficient product formation suggest that the reaction does not contribute significantly to the kinetics of triplet decay. By contrast, the observed lifetime is consistent with previous observations with p , p '-disubstituted benzophenones that undergo an efficient self-quenching process by a reductive charge transfer mechanism.