Dual‐Mode Ion‐Pair Charge‐Transfer Organic Nanoparticles From Fluorescent Viologens for Amine Sensing and Encrypted Data Storage

ABSTRACT To overcome the intrinsic drawbacks of conventional viologens, such as slow optical response and poor radical stability, we synthesized a series of viologen derivatives ( BTV , NTV , and STV ) by incorporating thiazolo[5,4‐d]thiazole units into bipyridine cores, followed by N ‐substitution with benzyl, naphthylmethyl, and propanesulfonate groups. These derivatives self‐assemble into donor–acceptor ion‐pair charge‐transfer organic nanoparticles (IPCT‐ONs) that exhibit redshifted UV–Vis absorption and fluorescence emission, thereby extending the visible‐light response. X‐ray photoelectron spectroscopy (XPS) analysis and DFT results confirmed electron transfer from tetraphenylborate anions to viologen moieties. The IPCT‐ONs display rapid and reversible photochromism, with distinct color transitions occurring within 30 s under 365 nm irradiation in an Ar atmosphere ( BTV / NTV : yellow → green → blue; STV : yellow → purple), which remain effective even when embedded in polyvinyl alcohol (PVA) films. They demonstrate dual‐mode amine sensing, wherein ethylenediamine induces both a colorimetric shift (yellow → blue–violet) and fluorescence quenching at 470 nm, enabling sensitive and selective detection of toxic amines. Additionally, this IPCT nanoparticle platform offers applications in real‐time light intensity monitoring, anti‐counterfeiting measures, and ink‐free printing.