Fluorogenic sulphate anion sensor with INHIBIT logic gate by dinuclear Zn (II) complex: Synthesis, emission, DFT studies

Abstract

N4O3 coordinating heptadentate non emissive ligand emits strong blue emissive light only in the presence of Zn(II) ion. This ligand yields a solid crystalline μ-phenoxo bridge dinuclear Zn(II) complex 1a. The binding stoichiometry, binding constant and binding affinity of the complex in solution state has been studied here. The UV–vis, Emission, 1H NMR and ESI-MS several spectroscopic ratiometric titration of the ligand in presence of zinc ion revealed that the major part of the solution contained dinuclear form of the complex over the mononuclear form. Theoretical interpretation also justifies this dimeric behavior of the complexation in solution state. The complex was examined with varied types of anions, such as H2PO4□, HPO42−, PO43−, SO42−, F−, Br−, Cl−, I−, AcO−, NO3–, ATP and ADP. The dinuclear species was found to act as a highly selective and sensitive receptor for tetrahedral SO42− by fluorescence ON-OFF signaling through the formation of sulphato bridging dinuclear complex 1b. The photo physical properties of both the complexes have been correlated by DFT and time-dependent DFT (TDDFT) method. The emission intensity changes of this dinuclear complex during the addition of sulphate anion is useful to construct an INHIBIT logic gate at the molecular level, by means of Zn2+ and SO42− ions as chemical inputs and the emission intensity as output signal.