A general method for near-infrared photoswitching in biology, demonstrated by the >700 nm photocontrol of GPCR activity in brain slices

Azobenzene molecular switches are widely used to photocontrol material properties, and biological activity in cell culture, via photoisomerisation between E and Z isomers. However, because population photoswitching is incomplete, their dynamic range of property control is often small; and because they cannot be operated with red/NIR light, they are usually not applicable in deep tissue. Here, we demonstrate a general method for efficient single-photon photocontrol of azobenzenes, and of glutamate receptor activity, at >700 nm in live tissue. We use red/NIR chromophore auxiliaries to perform intramolecular energy transfer to bioactive azobenzenes, which drives fast bulk Z→E isomerisation up to even >97% completeness. The auxiliary/azobenzene dyads allow >700 nm photoswitching with photon-efficiency that can be even higher than for direct azobenzene E→Z isomerisation in the UV region; and they are biocompatible and photostable. Crucially, their performance properties are intrinsic, i.e. auxiliary-based intramolecular switching will perform identically at any dilution and will not be affected by biodistribution. We show that these dyads can be created straightforwardly from most azobenzene systems, with most auxiliary chromophores, without tricky molecular redesign or re-optimisation. After outlining some rules of auxiliary-based photoswitching, which can guide its broader adoption, we conclude by using dyads to make the first demonstration of single-photon NIR chemical photoswitching control over biological activity, in cell culture and intact brain tissue.