A thiadiazole-functionalized Zn(II)-based luminescent coordination polymer with seven-fold interweaved herringbone nets showing solvent-responsive fluorescence properties and discriminative detection of ethylenediamine

Abstract

A benzothiadiazole-functionalized luminescent Zn(II) coordination polymer (CP) {[Zn2(bcpBTD)2(bpBTD)(H2O)2]∙DMF}n (1, H2bcpBTD = bis(4-carboxyphenyl)benzothiadiazole, bpBTD = bis(pyridin-4-yl)benzothiadiazole, DMF = N,N-dimethylformamide) has been successfully constructed. Compound 1 has a two-dimensional (2D) 3-connected (6,3) herringbone net, which is interweaved by other six identical nets in a 7-fold 2D + 2D → 2D interweaved manner. XRPD patterns proved that 1 is highly stable in common solvents, including H2O, acetone, CH3CN, CH2Cl2, N,N-dimethylacetamide (DMAc), DMF, CH3OH, and toluene, and in pH 2–11 aqueous solutions for 5 days. Upon irradiation, 1 emitted green light fluorescence in solid-state and solvent-responsive bright fluorescence in suspension-phase varying from pale-blue light in toluene, CH3CN, CH2Cl2, and acetone to blue-cyan light in CH3OH, DMF and DMAc, and to green light in H2O. In addition, the emission intensity of 1 was greatly enhanced in pH 10 and 11 aqueous solutions but much weaker and less sensitive to other pH values (pH = 4–9, 12, and 13). Of particular note, the H2O suspension of 1 is capable of detection of ethylenediamine (en) through a remarkable fluorescence enhancement (turn-on) response, with excellent sensitivity as low as 0.87 μM (corresponding to 0.052 ppm). The discriminative en detection is properly interpreted by the cooperative effects of absorbance caused enhancement (ACE) and the amine basicity.