Phototriggered Supramolecular Polymerization

Photo‐initiated supramolecular polymerization of a naphthalenediimide (NDI‐1) derivative containing an ortho‐nitrobenzyl (ONB)‐protected amide group is demonstrated. In a hydrocarbon solvent (methylcyclohexane), it remains as monomer. Upon photo‐irradiation, deprotection of the ONB group produces NDI‐2 with a free amide group, which drives supramolecular polymerization by self‐complementary H‐bonding between the amide groups, leading to gelation. The polymerization rate can be controlled by tuning the energy of the light source. During photopolymerization, a gradual increase in hydrodynamic radius and viscosity is noticed. More interestingly, the morphology of the supramolecular polymer of NDI‐2, produced by photo‐irradiation, was a spherulite, which is in sharp contrast with the fibrillar morphology of NDI‐2 polymer, when assembled spontaneously without a phototrigger. This is ascribed to the ability of the ONB‐caged pro‐monomer (NDI‐1) to act as a chain‐stopper by forming a H‐bonded complex with the active monomer during the growth of the supramolecular polymer under photo‐irradiation.