Conformational and Electrostatic Control of PET in TTz–TPA Fluorophores for Butyl Nitrite Vapor Sensing

Abstract

This work presents a conformation-regulated donor–acceptor–donor (D–A–D) platform based on thiazolo[5,4-d]thiazole (TTz) and triphenylamine (TPA) to reveal how kinetic accessibility controls photoinduced electron transfer (PET) toward butyl nitrite. Para/ortho methoxy substitution on the TPA donors modulates electron-density distribution and steric/conformational accessibility, producing distinct recognition regimes despite comparable thermodynamic feasibility for PET. TTz-1 shows no detectable interaction, TTz-2 undergoes collision-controlled dynamic quenching, and TTz-3 forms a ground-state association leading to a static–dynamic mixed mechanism. Spectroscopy, femtosecond transient absorption, 1H NMR titration, and DFT/TD-DFT calculations identify electrostatic anchoring and spatial accessibility as decisive parameters that determine whether PET is kinetically realized. As solid-state fluorescent films, the probes enable butyl nitrite vapor sensing with a lowest detectable concentration of 6.4 ppt and a fast response time of 5 s. This study establishes a structure–recognition–function framework for designing fluorescent sensors for volatile electron-deficient analytes.