Unimolecular multi-color photoswitching via imidazole-fused tetraarylethylene: photochromism, ion sensing and applications

Three imidazole-fused tetraarylethylene fluorescent probes (TPT-DPIo, TPT-PIo, and TPT-PHIo) featuring a unified molecular scaffold that integrates photochromism, multi-analyte sensing, and unimolecular photoswitching were developed. Upon 365 nm irradiation, these compounds undergo ultrafast photocyclization with concomitant photo-oxidative activation, generating irreversible fluorescence enhancement. Crucially, they enable anion/cation-discriminative detection: hydrogen bonding interaction by CN⁻/F⁻ induces the unaided eye visible color shifts, while Zn²⁺/Cd²⁺ binding with TPT-PHIo triggers large Stokes shifts (Δλ_em = 104 nm for Zn²⁺, 70 nm for Cd²⁺), accompanied by emission color transitions from dark blue (λ_em,TPT-PHIo = 456 nm 456 nm) to green or yellow. Importantly, the presence of CN⁻, F⁻, Zn²⁺ and Cd²⁺ can remarkably activate the photocyclization reaction, achieving multi-color switching within a single molecular platform. Practical utility was demonstrated through test strips for on-site CN⁻/F⁻ and Zn²⁺/Cd²⁺ detection, alongside live-cell imaging with >90 % viability, confirming their dual functionality as environmental sensors and biocompatible bioimaging agents. This work provides analyte-gated photoresponsive materials for adaptive optoelectronic applications.