Photoresponsive Metallo-Supramolecular Systems Constructed From a Bidentate Ligand

Metallosupramolecular polymers (MSPs) are stimuli-responsive materials whose properties can be tailored through the choice of ligand and metal salt. Their dynamic behavior is governed by the reversibility of the metal-ligand (ML) complexes and the ability to shift the equilibrium between assembled and disassembled states, enabling functions such as recyclability, healability, and adaptability. While heat is a simple and efficient stimulus, it makes temporal and spatial control difficult to achieve. To address this, we developed MSP systems composed of copolymers bearing 6-(1'-methylbenzimidazolyl)pyridine (MBP) ligands in varying concentrations, metal salts, and the photoacid generator (PAG) 2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine (MBTT). The MBP groups coordinate Fe(OTf)₂ or Fe(OTf)₃ to form dynamic ML cross-links. The resulting networks produce robust organogels when imbibed with chlorobenzene. MBTT renders the systems optically responsive, as UV light triggers the release of acid, which protonates and dissociates the ML cross-links, thereby inducing network disassembly. We characterize the MSP organogels using rheology and monitor acid-induced responses via UV-vis spectroscopy on model complexes. Opto-rheological experiments reveal that softening is possible with as little as 0.25 equivalents of MBTT per ML complex and that excellent temporal control is possible.