A new benzimidazole‐based selective and sensitive ‘on–off’ fluorescence chemosensor for Cu 2+ ions and application in cellular bioimaging

Two new twinborn benzimidazole derivates ( L and A ), which bonded pyridine via the ester space on the opposite and adjacent positions of the benzene ring of benzimidazole respectively, were designed and synthesized. Compound L displayed fluorescence quenching response only towards copper(II) ions (Cu 2+ ) in acetonitrile solution with high selectivity and sensitivity. However, compound A presented ‘on–off’ fluorescence response towards a wide range of metal ions to different degrees and did not have selectivity. Furthermore, compound L formed a 1:1 complex with Cu 2+ and the binding constant between sensor L and Cu 2+ was high at 6.02 × 10 4  M −1 . Job's plot, mass spectra, IR spectra, 1 H‐NMR titration and density functional theory (DFT) calculations demonstrated the formation of a 1:1 complex between L and Cu 2+ . Chemosensor L displayed a low limit of detection (3.05 × 10 −6  M) and fast response time (15 s) to Cu 2+ . The Stern–Volmer analysis illustrated that the fluorescence quenching agreed with the static quenching mode. In addition, the obvious difference of L within HepG2 cells in the presence and absence of Cu 2+ indicated L had the recognition capability for Cu 2+ in living cells.