Stepwise functionalization-induced molecular tweak unveiling multi-level thermochromic data encryption and...

Protecting hierarchical data via multi-level encryption and authenticating high-contrast touch traces represents an emerging frontier demanding technological innovation in molecular materials. Herein, via precise molecular interventions, three D-A-A' (donor-acceptor-acceptor) type aggregation induced emission (AIE)-active positional isomers (p-TPy, m-TPy, and o-TPy) are designed by varying the pyridine ring position in the acceptor. Their systematic investigation reveals key photophysical and structure-property insights, revealing their potential in advanced security and encryption. Positional modulation regulates electron-accepting strength and molecular packing, leading to red-shifted solid-state emission and influencing PLQY, transient PL, solvatochromism, and thermal stability as supported by crystal analysis and theoretical calculations. These stimuli-adaptive isomers address two critical challenges in advanced security systems. First, thermochromic luminescent materials (TLMs) exhibiting multiple temperature-dependent luminescent states are formulated as security inks by doping the para-isomer into phase-change matrices, enabling a multi-level security system. Second, a red-emissive, water-soluble amphiphilic fluorescent probe is obtained by functionalizing the para-isomer into a pyridinium emitter (p-TPyMe), capable of detecting latent fingerprints on diverse substrates and revealing level-3 ridge details with an exceptional contrast value of 5.39. These results demonstrate how molecular design in single chromophores translates into strategic AIE-active stimuli-adaptive positional isomers with intricate structure-property relationships, highlighting their potential for next-generation anti-counterfeiting, data encryption, and forensic technologies.