Photoswitching Azo Compounds in Vivo with Red Light

The photoisomerization of azobenzenes
provides a general means
for the photocontrol of molecular structure and function. For applications
in vivo, however, the wavelength of irradiation required for trans-to-cis
isomerization of azobenzenes is critical since UV and most visible
wavelengths are strongly scattered by cells and tissues. We report
here that azobenzene compounds in which all four positions ortho to
the azo group are substituted with bulky electron-rich substituents
can be effectively isomerized with red light (630–660 nm),
a wavelength range that is orders of magnitude more penetrating through
tissue than other parts of the visible spectrum. When the ortho substituent
is chloro, the compounds also exhibit stability to reduction by glutathione,
enabling their use in intracellular environments in vivo.