A perylene diimide-based near-IR ratiometric sensor for detection of Cu2+ ions: ensemble for discrimination of CN− and S2− ions

Abstract

In this study, we have designed and synthesized a perylene diimide-based novel chromo-fluorescent chemosensor (TBP-PDI), which shows selective ratiometric fluorescent ‘turn-on’ (F₄₈₂/F₆₈₀ nm) and colorimetric (A₄₇₆/A₆₃₀) responses on addition of Cu²⁺ ions in a HEPES buffer : CH₃CN (4 : 6, v/v, pH 7.2) medium and CH₃CN. The detection limits of TBP-PDI for Cu²⁺ were found to be 4.8 μM/2.5 nM using fluorescence mode and 5.22 μM/0.71 nM using absorbance mode in these solvents, respectively. The complexation of TBP-PDI with Cu²⁺ was further supported by NMR, dynamic light scattering (DLS), cyclic voltammetric (CV) and differential pulse voltammetric (DPV) studies. The limit of detection for Cu²⁺ using DPV is 0.46 μM. This perylene diimide–Cu²⁺ based ensemble (TBP-PDI–Cu²⁺) was further used as a ‘turn-on’ type chemosensor for CN⁻ ions with a detection limit of 7.38 nM/3.98 μM and as a ‘turn-off’ type chemosensor for S²⁻ with a detection limit of 35 μM. These changes can be explained by the fact that CN⁻ interacts with the TBP-PDI–Cu²⁺ ensemble through coordination with Cu²⁺via displacement of solvent molecules whereas S²⁻ interacts with the TBP-PDI–Cu²⁺ ensemble via sequestration of Cu²⁺ from the binding pocket of the ensemble.