Benzothiazole-Based AIEgen with Tunable Excited-State Intramolecular Proton Transfer and Restricted Intramolecular Rotation Processes for Highly Sensitive Physiological pH Sensing

In
this work, a benzothiazole-based aggregation-induced emission
luminogen (AIEgen) of 2-(5-(4-carboxyphenyl)-2-hydroxyphenyl)­benzothiazole
(3) was designed and synthesized, which exhibited multifluorescence
emissions in different dispersed or aggregated states based on tunable
excited-state intramolecular proton transfer (ESIPT) and restricted
intramolecular rotation (RIR) processes. 3 was successfully
used as a ratiometric fluorescent chemosensor for the detection of
pH, which exhibited reversible acid/base-switched yellow/cyan emission
transition. More importantly, the pH jump of 3 was very
precipitous from 7.0 to 8.0 with a midpoint of 7.5, which was well
matched with the physiological pH. This feature makes 3 very suitable for the highly sensitive detection of pH fluctuation
in biosamples and neutral water samples. 3 was also successfully
used as a ratiometric fluorescence chemosensor for the detection of
acidic and basic organic vapors in test papers.