A camphor-based Schiff base fluorescent probe for detection of alkaline pH and its applications in living cells

ABSTRACT In this work, a novel fluorescence “turn-on” probe CADB was designed and synthesized by the condensation reaction of camphor-derived quinoxalin-1,4-diamine (2) and 4-bromo-2-hydroxy-benzaldehyde. This fluorescent probe could detect the pH change in alkaline environment with high selectivity, fast response time, good reversibility, and large Stokes shift. CADB displayed a good linear relationship between the fluorescence intensity at 491 nm and the pH values ranging from 9.65 to 11.68 with a pKa of 10.62. The sensing mechanism of CADB towards alkaline pH was well confirmed by 1H NMR titration and density functional theory (DFT) calculations. Additionally, the probe CADB could serve as a reliable method for biological imaging of alkaline pH in living zebrafish.