Bisbenzimidazoles with Benzenediyl Spacer: An Efficient Fluorophore for Dihydrogenphosphate Sensing and Targeted Living Cell Imaging

Abstract

A bisbenzimidazole-based fluorescent probe (PBZ) has been developed for the selective detection of dihydrogen phosphate (H₂PO₄⁻) ions in a CH₃CN–water (7:3, v/v) mixed solvent system. The probe exhibited pronounced spectral responses upon interaction with H₂PO₄⁻, including the emergence of a new charge-transfer absorption band and a distinct fluorescence turn-off behavior. PBZ displayed excellent selectivity toward H₂PO₄⁻ over other competing anions and demonstrated a limit of detection (LOD) of 1.87 µM. Binding analysis, supported by density functional theory (DFT), confirmed the formation of a stable 1:1 hydrogen-bonded host-guest complex with H₂PO₄⁻. Furthermore, the probe showed rapid response, good solvent compatibility, low cytotoxicity, and effective intracellular fluorescence imaging in A549 cells, demonstrating its potential as a biocompatible chemosensor for phosphate monitoring in environmental and biomedical applications.