Proximal Photocleavage: Controlling Polymer Solubility through Pathway Dependent Wavelength-Orthogonal Photoreactions

Current families of reversible photochemical reactions present challenges for light-controlled polymers of either photostationary states, which are common in photoinduced cycloaddition/cycloreversion reactions, or exclusively intramolecular bond changes, which characterize most photochromic units. In response to these challenges, here the concept of “proximal photocleavage” is presented, which combines photochemical crosslinking with a photocleavable linker, enabling a one-time bond formation/cleavage sequence. Proximal photocleavage methacrylate monomers comprising, in series along the pendant of the methacrylate, a coumarin unit for crosslinking and either a phenacyl or ortho-nitrobenzyl photocleavable group for decrosslinking are reported. The photophysical properties of these monomers and their statistical copolymers with methyl methacrylate are described, and wavelength selective crosslinking and de-crosslinking of thin polymer films are demonstrated.