A dual-phase coumarin-based ratiometric fluorescent probe for highly sensitive cyanide sensing and bioimaging applications.

A coumarin-based fluorescent probe, DHMH, was synthesized for the sensitive and selective detection of cyanide ions (CN-) over other competing anions. This probe exhibited a dual recognition mechanism for cyanide through a change in its ratiometric emission in both solution and solid phases. The chemical structure of DHMH was characterized using several spectroscopic techniques. In solution, an adduct was formed after the incremental addition of cyanide to DHMH through a mechanism involving deprotonation with nucleophilic addition, thereby leading to a hypsochromic shift. On the other hand, in the solid phase, the interaction was attributed exclusively to nucleophilic addition, thereby resulting in a bathochromic shift. The sensing mechanism for cyanide detection was explored through 1H-NMR titration, mass spectrometry, infrared spectroscopy and density functional theory (DFT) calculations. The detection limit of DHMH for CN- was determined to be (0.64 ± 0.13) × 10-6 M. DHMH demonstrated outstanding performance in real water samples, confirming its practical applicability for environmental monitoring. Furthermore, DHMH successfully facilitated the live-cell imaging of intracellular cyanide, showcasing its potential for biological and environmental cyanide sensing. This work highlights DHMH as a versatile sensor with broad application prospects in chemical sensing and bioimaging.