Proton donor modulating ESIPT-based fluorescent probes for highly sensitive and selective detection of Cu2+

Abstract

Two novel ESIPT-based fluorescent probes, N-(2-(1-(p-tolyl)-1H-phenenanthro[9,10-d]imidazol-2-yl)phenyl) picolinamide (Pi-A) and 2-(1-(p-tolyl)-1H-phenanthro[9,10-d]imidazol-2-yl)phenylpicolinate (Pi-E), were designed and synthesized. The favorable features of the proposed probes included excellent water solubility, wide pH range, high selectivity and sensitivity to Cu²⁺. Interestingly, the difference in the linker of the probe molecules led to a radical change in the fluorescent response of the probes to Cu²⁺. Pi-A showed fluorescence turn-off towards Cu²⁺ with a detection limit of 1.6 × 10⁻⁹ M and Pi-E showed fluorescence turn-on towards Cu²⁺ with a detection limit of 1.8 × 10⁻⁸ M in the same condition. The Cu²⁺ recognition mechanisms of the probes were investigated by Job's plot analyses, NMR and ESI-MS spectroscopy experiments. Moreover, our experiments also showed that the probes are of excellent cell permeability and are capable of imaging Cu²⁺ within living cells.