Key points are not available for this paper at this time.
Hip to be square: Styrenes participate in 2+2 cycloadditions upon irradiation with visible light in the presence of an iridium(III) polypyridyl complex. In contrast to previous reports of visible light photoredox catalysis, the mechanism of this process involves photosensitization by energy transfer and not electron transfer.
Lu et al. (Mon,) studied this question.