Multiresponsive Nonconjugated Polyelectrolyte Fluorescence Films

Fluorescent functional polyelectrolytes have been extensively applied in biomedicine and sensing technologies. Classic fluorescent conjugated polyelectrolytes involve complicated synthetic procedures. From a technological point of view, developing such materials via a straightforward synthetic route is desirable; however, attempts to achieve this have been largely unsuccessful. Herein, we introduce a new class of nonconjugated fluorescent polyelectrolytes (Poly(1,2,4-triazolium)s, Ptriazs) that exhibit a broad fluorescence tuning range. This was achieved simply by changing the pendant groups attached to the cationic poly(1-vinyl-1,2,4-triazolium) main chains. Experimental and theoretical studies revealed that the fluorescence modulation was achieved through-space charge transfer driven by π-π, cation-π, and H-bonding interactions. Notably, stable and uniform-sized aqueous colloidal nanoparticles of Ptriazs can be readily made via precipitation polymerization method in water. We discover that bulk and nanoparticle Ptriaz films exhibit reversible excitation wavelength-dependent emission and water/temperature-responsive fluorescence changes. These unique multiresponsive characteristics enable Ptiraz films to achieve multimodal optical encryption with security encoded by a myriad of external stimuli. These findings favor the scalable and rational development of nonconjugated fluorescent functional polyelectrolytes with strong potential for a wide range of applications.