Matrix-Modulated Protonation Decoupling in Acrylonitrile Fluorophores: Toluene-Swollen PMMA for Multilevel Encryption...

Stimuli-responsive organic fluorophores are fundamental candidates for high-security information encryption and intelligent molecular devices. Nevertheless, conventional acid-responsive systems suffer from uncontrolled protonation kinetics, simple binary optical switching, and limited capability to regulate solid-state sequential protonation. Herein, we construct a library of thiophene-acrylonitrile proton-responsive fluorophores bearing pyridine and dimethylamino terminal groups. The acrylonitrile-conjugated scaffold tunes proton affinity and frontier orbital energies, enabling solvent-dependent sequential protonation with distinct acid thresholds for different basic sites. Combined spectroscopic characterizations and quantum chemical calculations reveal the structure-protonation-photophysics correlation, confirming that stepwise protonation at two independent sites triggers tunable absorption and emission shifts. The key novelty of this work lies in matrix-mediated decoupling of sequential protonation: embedding the fluorophore within poly(methyl methacrylate) (PMMA) drastically alters protonation behavior relative to solution, since the polymer matrix restricts molecular and proton diffusion and suppresses full dual protonation. Toluene vapor-induced matrix swelling relieves these physical constraints and reactivates the sequential protonation cascade, delivering unique acid-solvent dual responsiveness exclusively accessible in solid polymer films. Utilizing this switchable protonation pathway, we realize ternary information encryption and a molecular SR logic gate, enabling hierarchical information release, decoy information masking, and precise chemical-to-optical signal conversion for multi-level data storage. This work establishes a matrix-modulated strategy to manipulate stepwise protonation in solid-state media, offering a versatile platform for high-capacity anti-counterfeiting tags and intelligent molecular optical devices.