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.

偶氮苯的光异构化反应，为分子结构与功能的光调控提供了通用手段。然而，若将其应用于活体（in vivo）场景时，偶氮苯反式-顺式异构化所需的照射波长至关重要——这是因为紫外线与多数可见光波段极易被细胞和组织强烈散射。本研究报道，在偶氮基团邻位的四个位点均带有大体积富电子取代基的偶氮苯类化合物，可通过红光（630–660 nm）实现高效异构化；该波长范围的光线穿透生物组织的能力，相较于可见光光谱其余波段高出数个数量级。当邻位取代基为氯原子时，此类化合物还具备抗谷胱甘肽还原的稳定性，可用于活体的胞内环境。