Executive Summary : | Tunable luminescence in hydrogel materials is a research area of topical interest since these materials have potential applications in diverse settings, such as, sensing, bioimaging, reversible information encryption-decryption and flexible displays. Photoluminescent hydrogels also have potential applications as biomimetic shape and color changing materials that may mimic the adaptive optical response of bioluminescent marine organisms. White light emitting self-assembled materials are particularly interesting for their chromic response with high sensitivity to different external stimuli because of the presence of multiple peaks in the emission spectrum. Our current proposal aims to obtain mechanically strong and stretchable self-healing multi-color tunable photoluminescent hydrogel platform that employs lanthanide-sensitizer (terpyridine/dipicolinate) interaction and hydrophobic association as dual physical cross-links and reversible sacrificial motifs. The terpyridines/dipicolinate sensitize lanthanide ions in the sequestered hydrophobic environment of anionic micelles. This strategy overcomes the luminescence quenching of Ln3+ ions in aqueous medium, ensures proximal sensitization of Ln3+ ions and employs Ln3+-ligand reversible cross-links in the hydrogel. The application of these hydrogels will be investigated as transition metal ion based luminescence ON-OFF-ON switch to sense beta lactamase, an enzyme that plays an important role in metabolic degradation of penicillin, which is an important beta-lactam antibiotic. To demonstrate multi-functional application of this hydrogel setting, a composite hydrogel will be realized by combining the Ln3+ hydrogel with aggregation induced emission (AIE) active fluorophores. For this purpose, tetraphenylethene (TPE) will be integrated into a thermosensitive poly(N-isopropylacryamide) linear chain. This linear Poly(NIPAM-TPE chain) will be interpenetrated into the Ln3+ hydrogel matrix to achieve independent control of cyan fluoresecence from aggregated TPE and red/green light emission from sensitized Ln3+ centers. Hence, a continuous spectrum of emission in the visible range is achievable by tuning the respective concentrations of the Poly(NIPAM-TPE chain) and the Ln3+ ions. Stimuli-responsive photoluminescence tuning of these Ln3+-TPE hydrogels will be studied. White light emission can be achieved by tuning the individual emission of cyan (a mixture of green and blue) from TPE center and the red emission from the Eu3+ center. Utilizing the thermoresponsive collapse of the NIPAm chain and subsequent enhancement of cyan fluorescence from the AIE-active TPE units, synergistic multi-color tunable fluorescence and shape changing actuation of the hydrogels can be realized. Biomimetic camouflaging skin with adaptable fluorescence will also be demonstrated. These bio-inspired smart luminescent materials may find applications in sensors, displays, biomimetic actuation and camouflaging actions in soft robotics. |