Bypassing the energy barrier of homolytic photodehalogenation in chloroaromatics through self-quenching.

Reductive photodehalogenation of chloroaromatics is assumed to proceed from the triplet excited state, although its energy is often insufficient to promote a clean homolytic C-Cl cleavage. A clear-cut experimental proof is provided that correlates self-quenching of the directly observed triplet excited states of chlorocarbazole-based dyads 1 and 2 with photoreactivity via intramolecular charge transfer.