Ultrasound effects on the photopinacolization of benzophenone

Ultrasonic irradiation is able to modify the course of several photochemical reactions, especially bimolecular, proceeding via triplet states. These effects were illustrated in the study of benzophenone photopinacolization in ethanol. The rates and yields increase when sonication is applied simultaneously to UV irradiation. An explanation is based on a 2-fold effect: (i) light-absorbing transient species undergo sonolytic decomposition, making the photoconversion more efficient, and (ii); sonication induces the triplet state quenching, as shown by Stern-Volmer plots from experiments run in the presence of naphthalene, probably due to the easier collisional deactivation processes favored by the homogeneous distribution of the activated species.