Modeling Absorption Spectra of Optically Switchable Azobenzenes

Azobenzenes have the unique ability to undergo reversible isomerization between two geometrical isomers (the straight trans form and the bent cis) when exposed to certain wavelengths of light, which provide energy for the change. Thus, when embedded in liquid crystal matrices, azobenzene derivatives can function as optically triggered switches regulating, for example, membrane permeability to gases. An optimal azobenzene for this application would have an energy barrier low enough to facilitate changes from trans to cis and back again, but high enough so that such changes would remain stable. In order to identify such suitable azobenzenes, a series of azobenzene derivatives were modeled using computer software. The resulting data were compared, and it was found that nitro groups lowered both thermal and photochemical barriers, while aminoester groups increased the thermal relaxation barriers. Thus, it seems feasible to engineer azobenzene derivatives specifically for use as optical switches in these doped membranes.