A new near-infrared ratiometric fluorescent probe using conjugated dicyanoisophorone and quinoline with double vinylene linkers for sensing of pH and its application

pH plays a crucial role in multiple biological processes, therefore, the development of pH imaging and measurement using the fluorescent probes in biological systems is highly active and has an urgent demand. In this work, a new ratiometric near-infrared (NIR) fluorescent probe DCIQ based on conjugated dicyanoisophorone and quinoline with double vinylene linkers was obtained for pH sensing. The remote conjugated quinoline and middle phenol used as an acceptor for protons may induce dual-modal colorimetric and fluorescence changes as a function of tiny variations in pH in the range of 6-8. Compared to previously reported probes, the proposed DCIQ probe was advantageous in terms of near-infrared emission signal (734 nm), large Stockes shift (173 nm), high selectivity, and good sensitivity. In addition, DCIQ could be as potential probe for viscosity by the fluorescence change. Moreover, the DCIQ-immobilized test papers exhibited reversible colorimetric changes as a function of variations in the environmental acid/base (>4 cycles) through naked-eye colorimetric detection. The desirable pKa (7.24) indicated that DCIQ probe could be used as a molecular tool for readily entering living cells with low cytotoxicity. Importantly, the DCIQ probe was successfully demonstrated for real-time detection of pH fluctuation in HeLa cells through ratiometric fluorescence images.