Triplet Energy and π-Conjugation Effects on Photoisomerization of Chiral N,C-Chelate Organoborons with PAH Substituents.

Chiral, PAH substituted N,C-chelate boron compounds are systematically investigated to establish the effect of triplet energy and substitution position on their photoreactivity. They all undergo regioselective photoisomerization, forming new dark isomers with quantum efficiencies reflecting these various factors. New PAH fused 4bH-azaborepins are obtained via thermal isomerization of the dark isomers. These results further implicate a photoactive triplet state in the photoisomerization process and its utility in achieving rare PAH-fused azaborepin-like heterocycles.