ABSTRACT Ratiometric fluorescence sensing offers superior interference resistance and self‐calibration, yet designing these probes remains challenging due to a lack of generalizable mechanisms. Herein, we introduce a novel, mechanism‐driven strategy based on the twisted intramolecular charge shuttle (TICS) process to achieve ultrafast, sensitive nitrite (NO 2 − ) ratiometric detection. By strategically installing an o‐phenylenediamine (OPD) fragment at the reactive meso‐position of a pyronin fluorophore, we successfully induced and modulated the TICS process through a specific reaction with NO 2 − . This generates a robust ratiometric response with a remarkably low detection limit (6.6 nM) and an ultrafast response time of 18 s—two orders of magnitude faster than the classical Griess method. To demonstrate practical utility, we incorporated the probe into a portable device for rapid, visual on‐site quantification of nitrite in food and water. Furthermore, the probe successfully imaged endogenous NO 2 − dynamics in living plants, revealing a direct correlation between nitrite fluctuations and environmental stress. This study establishes TICS as a powerful platform for probe design, marking a significant transition from empirical dye screening toward rational, mechanism‐driven molecular engineering.
Ye et al. (2026) studied this question.