Robust Fluorescent Eutectogel with Temperature Resilience and Microenvironment-Regulated Emission for Stimuli-Responsivity

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Fluorescent eutectogels, as emerging smart materials that integrate the unique microenvironment, excellent temperature resistance, and eco-friendliness of deep eutectic solvents (DESs), have driven remarkable advancement in flexible optical materials and information encryption. Here we report a transparent fluorescent eutectogel prepared by incorporating the environmentally sensitive cationic luminophore 2,5-bis(2-pyridiniumyl)-1H-pyrrole bis(hexafluorophosphate) ([H3DPP]2+) into a glycerol/Zn(NO3)2·6H2O DES followed by in situ photopolymerization of acrylamide. The nitrate-containing DES strongly reshapes the photophysical behavior of [H3DPP]2+, producing a pronounced red shift and enhanced emission relative to glycerol or aqueous Zn(NO3)2 solution. The addition of monomer has little influence on the DES-regulated emission, whereas gel-network formation causes only moderate fluorescence attenuation while largely preserving the DES-defined emissive state. Spectroscopic analysis and DFT/TD-DFT calculations indicate that directional hydrogen-bonding interactions between NO3– and the protonated/pyrrolic N–H sites of [H3DPP]2+ modulate its electronic structure and optical transitions. The resulting eutectogel exhibits high visible transparency, tensile strength of 230 kPa, stretchability of 820%, adhesion to diverse substrates (0.25 MPa on PTFE), and excellent solvent retention, maintaining 95% of its solvent after storage at 70 °C for 9 days. The fluorescence also remains visible after prolonged storage at 25, 70, and −25 °C. Moreover, relying on the high transparency, good mechanical properties and stimulus-responsive fluorescence characteristics of this eutectogel, localized chemical writing, UV-triggered visualization and barcode digital reading can be realized. This work demonstrates that DES-regulated microenvironments offer a robust platform for tuning molecular emission and developing stable, stimuli-responsive fluorescent soft materials for visual anticounterfeiting and information encryption.