title: Phototriggered Supramolecular Polymerization.
abstract: 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.
authors.affiliation: Polymer Science Unit, Indian Association for the Cultivation of Science, 2A and 2B Raja S. C. Mullick Road, Kolkata, 700032, India.
authors.forename: Deep Sankar
authors.initials: DS
authors.lastname: Pal
authors.affiliation: Polymer Science Unit, Indian Association for the Cultivation of Science, 2A and 2B Raja S. C. Mullick Road, Kolkata, 700032, India.
authors.forename: Haridas
authors.initials: H
authors.lastname: Kar
authors.affiliation: Polymer Science Unit, Indian Association for the Cultivation of Science, 2A and 2B Raja S. C. Mullick Road, Kolkata, 700032, India.
authors.forename: Suhrit
authors.identifier: http://orcid.org/0000-0003-4199-4382
authors.initials: S
authors.lastname: Ghosh
keywords: chain stoppers; gels; hydrogen-bonding; photo-triggered assembly; supramolecular chemistry