Regardless, substitutions (to adjust the photophysical properties of the photoswitch) are necessary for AzTG derivatives to be effective in vivo. Currently, canonical azobenzene is incorporated, which switches to the cis-configuration in response to UV-A light (360 nm) (Figure ). In addition to the possible risks associated with exposure to UV light, short wavelengths have limited depth of penetration in living tissue. As such, it is highly desirable to shift the cis-isomerization wavelength into the bio-optical window -between 650 and 900 nm -where light has the highest tissue penetration depth (wavelengths <650 nm and >900 nm are absorbed by haemoglobin and water respectively). This bathochromic shift of the cis-isomerization could be achieved by incorporating a di-ortho-fluoro di-orthochloro (DFDC) azobenzene, which allows photoswitching with deep red (660 nm) light. DFDC azobenzene also provides a manageable steric bulk, near-bistable isomers, and the opportunity to refine photophysical properties through substitutions at the meta-and para-positions. The corresponding fatty acids, incorporated in glycerophospholipids and vanillamides, have already been used to control membrane properties and biological functions.