Pyridine-Based Rigidochromic Fluorescent Security Ink

Abstract

Traditional fluorescent probes typically display blueshifted emission in rigidifying media; however, a newly developed class of rigidochromic fluorophores derived from phenanthridine demonstrates remarkable redshifted emission under similar conditions. Pyridine, with similar N-heterostructure to those of phenanthridine group, is considered a promising candidate for achieving comparable rigidity-induced redshift behavior. In this work, we synthesized eight organic fluorophores featuring diverse functional units and substitutes by systematically combining pyridine with carbazole, triazatruxene (TAT), and tetraphenylethylene (TPE), respectively. These molecules exhibit significant emission redshifts (up to 225 nm, a record high value ever reported) or notable emission intensity changes as the rigidity of the polymer matrix increases, along with unique acid responsiveness. The differences in polar-π interactions between fluorophores and polymers diversify the emission behavior, advancing the development of secure printing and intelligent optical materials. By embedding these fluorophores into polymer films with helical phase structures, redshifted emission with tunable chirality was achieved. Notably, leveraging the acid-responsive properties of these fluorophores, a time-dependent light-controlled dynamic encryption system was constructed, successfully enabling multi-level information encryption. This research greatly expands the scope of rigidochromic fluorophores, and their applications in anti-counterfeiting and information storage.