Electronic Structure-Tuned Solvatochromic Probes for TBET-Driven Ratiometric Detection of Phosgene in Solution and Polymer Films.

Phosgene, a highly toxic industrial chemical, necessitates rapid, reliable, and field-deployable detection technologies because of its widespread industrial use and the risk of accidental release. Herein, we report two ICT-based solvatochromic fluorophores, RHTH-NMe2 and RHTH-NEt2, constructed from rhodamine-thiophene-tetralone fusion frameworks for selective phosgene sensing. Both probes display pronounced solvent-dependent photophysical properties due to strong intramolecular charge transfer and high oscillator strengths linked to the S0 → S1 transition. When exposed to phosgene, nucleophilic acylation-induced spirolactam ring opening significantly alters the electronic structure and activates an efficient through-bond energy transfer (TBET) process. This process results in a remarkable ratiometric fluorescence enhancement. Spectroscopic investigations and TD-DFT calculations support the proposed sensing mechanism and the associated excited-state transitions. Remarkably, the probes exhibit exceptionally large Stokes shifts exceeding 200 nm. This allows for robust ratiometric visualization with minimal spectral overlap and background interference. To demonstrate practical applicability, wearable polymer-film badges and test-strip platforms were fabricated for real-time naked-eye detection of phosgene vapor under hand-held 365 nm UV illumination. Furthermore, FESEM analysis disclosed phosgene-induced morphological reorganization of the polymer matrix into a porous interconnected architecture, facilitating analyte diffusion and rapid solid-state sensing. This work establishes a synergistic ICT-TBET strategy for developing high-performance solvatochromic sensors for portable chemical safety monitoring and environmental surveillance.