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

A benzothiadiazole-functionalized luminescent Zn(II) coordination polymer (CP) {[Zn2(bcpBTD)2(bpBTD) (H2O)2]center dot 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 mu M (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.