Visible Light Switching of a BF2-Coordinated Azo Compound

Here we report the synthesis and characterization of a BF2-azo complex that can be induced to isomerize without the need of deleterious UV light. The complexation of the azo group with BF2, coupled with the extended conjugation of the N=N pi-electrons, increases the energy of the n-pi* transitions and introduces new pi-nonbonding (pi(nb)) to pi* transitions that dominate the visible region. The well separated pi(nb)-pi* 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.