A novel fluorescent sensor derived from benzimidazo[2,1-a]benz[de]isoquinoline-7-one-12-carboxylic acid for Cu²⁺, Cd²⁺ and PPi

Fluorescent sensor of N,N-bis(pyridin-2-ylmethyl)benzimidazo[2,1-a]benz[de]isoquinoline-7-one-12-carboxamide (L) was prepared. L not only showed fluorescence quenching towards Cu²⁺ with a detection limit of 1.2 × 10^-8 mol/L in acetonitrile-H₂O (9:1) buffer solution, but also showed fluorescence turn-on response with a blue shift towards Cd²⁺ with a detection limit of 1.5 × 10^-7 mol/L in the same condition. Moreover, the new formed [Cu(L)] complex was found to act as a selective 'turn-on' fluorescent probe for pyrophosphate (PPi) with detection limit of 8 × 10^-9 mol/L, and [Cd(L)] complex was found to act as a selective colorimetric fluorescent probe for PPi with detection limit of 2.4 × 10^-8 mol/L. Such behaviors confirmed L could be applied as fluorescent sensor to detect Cu²⁺, Cd²⁺ and PPi based on different mechanisms. The different binding mode and sensing mechanism of L with Cu²⁺ and Cd²⁺ was verified by DFT/TDDFT calculation using Gaussian 09.