Modulation of S and N Active Sites for Coordination Polymers to Achieve Enhanced Hg²⁺ Sensing Performances

It is challenging and vital to develop coordination polymers (CPs) with an outstanding sensing performance. In this work, CP-based sensors with active S and N sites are first exploited. Three new Cu-CPs [Cu(L)(SCN)₂·2DMF]_n (1), [Cu(L)(SCN)·2DMF]_n (2), and [Cu(L)(CN)·2DMF]_n (3) were successfully synthesized by 9,10-bis(di(pyrimidin-5-yl)methylene)-9,10-dihydroanthracene (L) and SCN^-/CN^- ligands. 1 demonstrates a 1D wavelike chain, fabricated by L bridges linking with Cu(SCN)₂ units. 2 exhibits a 2D (3,3)-connected network fabricated by SCN^-, 3-connected L, and Cu units. 3 exhibits a 3D framework, built by 4-connected Cu centers, CN^-, and L bridges. 1-3 have good water, pH, and thermal stabilities. 1 and 2 have uncoordinated S and N active sites and can detect Hg²⁺ through the fluorescence enhancing ("turn-on") effect. Meanwhile, 3 only has uncoordinated N active sites and shows a negative Hg²⁺ sensing ability. 1 and 2 have ultrahigh Hg²⁺ sensing sensitivity and selectivity. The K_SV and LOD of 1 toward Hg²⁺ are about 3 and 5 times superior to those of 2, separately. 1 and 2 represent the first S- and N-rich CP-based sensors and exhibit an excellent "turn-on" Hg²⁺ sensing capacity. Their "turn-on" Hg²⁺ sensing mechanism and difference sensing performances are discussed in detail.