Azobenzene Photoswitching without Ultraviolet Light

TLDR

Azobenzene photoswitches typically require UV light, limiting their use in biological systems due to potential cellular damage. Substituting all four ortho positions with methoxy groups in an amidoazobenzene shifts the trans n–π* band by ~35 nm, enabling green‑light (530–560 nm) trans‑to‑cis switching, while the cis state remains thermally stable (~2.4 days) and can be reversed with blue light (460 nm), allowing bidirectional UV‑free photoswitching.

Abstract

Most azobenzene-based photoswitches use UV light for photoisomerization. This can limit their application in biological systems, where UV light can trigger unwanted responses, including cellular apoptosis. We have found that substitution of all four ortho positions with methoxy groups in an amidoazobenzene derivative leads to a substantial (∼35 nm) red shift of the n−π* band of the trans isomer, separating it from the cis n−π* transition. This red shift makes trans-to-cis photoswitching possible using green light (530–560 nm). The cis state is thermally stable with a half-life of ∼2.4 days in the dark in aqueous solution. Reverse (cis-to-trans) photoswitching can be accomplished with blue light (460 nm), so bidirectional photoswitching between thermally stable isomers is possible without using UV light at all.