The influence of linker substitution on the fluorescence responsive sensing of isostructural coordination polymers: visual turn-on, ratiometric, and turn-off sensing in water

Four isostructural and isomorphous coordination polymers, {[Zn 2 (OH)(NO 2 -1,4-bdc) 1.5 (Cz-3,6-bpy)]·2H 2 O} n ( 1 ), {[Zn 2 (OH)(NO 2 -1,4-bdc) 1.5 (Cz-Pr-3,6-bpy)]·0.5H 2 O} n ( 2 ), {[Zn 2 (OH)(Br-1,4-bdc) 1.5 (Cz-3,6-bpy)]·H 2 O} n ( 3 ), and {[Zn 2 (OH)(Br-1,4-bdc) 1.5 (Cz-Pr-3,6-bpy)]·0.5H 2 O} n ( 4 ), where NO 2 -1,4-bdc = 2-nitrobenzene-1,4-dicarboxylate, Br-1,4-bdc = 2-bromobenzene-1,4-dicarboxylate, Cz-3,6-bpy = 3,6-bis(pyridin-4-yl)-9 H -carbazole, and Cz-Pr-3,6-bpy = 3,6-bis(pyridin-4-yl)-9- n -propyl-9 H -carbazole, have been hydro(solvo)thermally synthesized. Compounds 1-4 have similar two-dimensional layer structures simplified to rhombus grid-like sql nets in topology. Both nitro-substituted 1 and 2 are fluorescence silent, behaving as visual fluorescence turn-on sensors for the detection of Fe 3+ , Cr 3+ , and Al 3+ in water. Both bromo-substituted 3 and 4 emit strong cyan fluorescence and can be treated as visually ratiometric fluorescent sensors for the detection of Fe 3+ , Cr 3+ , and Al 3+ and visual fluorescence turn-off sensors for the detection of CrO 4 2− and Cr 2 O 7 2− in water, with high selectivity and sensitivity. The work clearly shows that the substituent (nitro and bromo) on the benzene-1,4-dicarboxylate linker has a great impact not only on essential luminescence properties but also the fluorescence responsive performances of coordination polymers. Linker substituents show great impacts on the luminescence properties and sensing performances of isostructural coordination polymers, causing turn-on or ratiometric sensing of Fe 3+ , Al 3+ , and Cr 3+ and turn-off sensing of CrO 4 2− and Cr 2 O 7 2− .