| Azobenzenes have been used for almost half a century to impart spatiotemporal control on biological systems by way of an external stimulus---light. A limitation of previously reported azobenzenes is the requirement for ultraviolet to blue light to promote trans-to-cis isomerization. Light in this range of the spectrum poorly penetrates tissue and is cytotoxic, limiting in vivo applications. Through design and synthesis of an azobenzene derivative with a fused dioxane ring and a methoxy substituent on each phenyl ring, we obtained a core structure with a bathochromically-shifted absorption spectrum. Further substitution with para pyrollidine moieties raised the pKa of this azobenzene such that a portion is protonated at physiological pH allowing it to absorb at wavelengths in the near-infrared region. The compound undergoes trans-to-cis isomerization with 720 nm light and relaxes back to the trans isomer with a half-life on the order of 1 s. |
