The transformation of the sensing effect is first studied by ligand engineering. Hg2+ causes serious harm. Therefore, developing rich Hg2+ sensors is very essential. Three distinct π-conjugated functional ligands 1-Naphthoic acid (1-NA), 9-Anthracenecarboxylic acid (9-AC), and 1-Pyrenecarboxylic Acid (1-PA) are deliberately selected to construct three new L-based luminescent coordination polymers (LCPs) Cd(L)2(1-NA)2n (1), Cd(L)(9-AC)2(H2O)n (2), and Cd(L)(1-PA)2n (3) (L = 4,4'-((9h-fluoren-9-yl)-methylene)-dipyridine). 1-3 exhibit distinct chain skeletons, luminescence, and Hg2+ sensing effects. 1 or 2 shows a 1-D sawtooth or linear chain, which is formed by L bridges linking with Cd(L)(1-NA)2 or Cd(9-AC)2(H2O) units, while 3 is a 1-D cluster chain skeleton, constructed by two kinds of 1-PA bridges linking with Cd(L)2+ units. Luminescence of 1 is originated from the 1-NA-L LLCT process, while the emission of 2 or 3 is based on that of 9-AC or 1-PA. Particularly, they exhibit distinct Hg2+ sensing effects. 1 can detect Hg2+ through fluorescence enhancement and blue-shift, which is first found in all LCP-based Hg2+ sensors; 2 only shows a negative Hg2+ sensing ability; 3 can detect Hg2+ through fluorescence quenching. The detection limits of 1 and 3 toward Hg2+ are 340 and 120 nM, respectively. The mechanisms of distinct sensing effects are explored. This work reveals the crucial role of ligand engineering in LCP-based sensors.
Zhang et al. (Fri,) studied this question.