Visible light switching of a BF2-coordinated azo compound.

Here we report the synthesis and characterization of a BF(2)-azo complex that can be induced to isomerize without the need of deleterious UV light. The complexation of the azo group with BF(2), coupled with the extended conjugation of the N═N π-electrons, increases the energy of the n-π* transitions and introduces new π-nonbonding (π(nb)) to π* transitions that dominate the visible region. The well separated π(nb)-π* transitions of the trans and cis isomers enable the efficient switching of the system by using only visible light. The complexation also leads to a slow cis → trans thermal relaxation rate (t(1/2) = 12.5 h). Theoretical calculations indicate that the absorption bands in the visible range can be tuned using different Lewis acids, opening the way to a conceptually new strategy for the manipulation of azo compounds using only visible light.