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

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' (F-482/F-680 nm) and colorimetric (A(476)/A(630)) 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 mu M/2.5 nM using fluorescence mode and 5.22 mu M/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 mu M. 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 mu M and as a 'turn-off' type chemosensor for S2- with a detection limit of 35 mu M. These changes can be explained by the fact that CN- interacts with the TBP-PDI-Cu2+ ensemble through coordination with Cu(2+)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.