Construction of pyridine-functionalized metal-organic frameworks for the detection of flazasulfuron

Two novel Cu-based metal-organic frameworks (MOFs), namely, poly[[aquadichlorido[μ₄-4'-(pyridin-4-yl)-[2,2':6',2''-terpyridine]-4,4''-dicarboxylato][μ₃-4'-(pyridin-4-yl)-[2,2':6',2''-terpyridine]-4,4''-dicarboxylato]tricopper(II)] monohydrate], {[Cu₃(C₂₂H₁₂N₄O₄)₂Cl₂(H₂O)]·H₂O}_n or {[Cu₃(PTP)₂Cl₂(H₂O)]·H₂O}_n, (I), and poly[[diaquabis[μ₂-4'-(pyridin-3-yl)-[2,2':6',2''-terpyridine]-4,4''-dicarboxylato]bis(μ₂-terephthalato)tricopper(II)] dihydrate], {[Cu₃(C₂₂H₁₂N₄O₄)₂(C₈H₄O₄)₂(H₂O)₂]·2H₂O}_n or {[Cu₃(BDC)₂(MTP)₂(H₂O)₂]·2H₂O}_n, (II), have been synthesized successfully with 4'-(pyridin-4-yl)-[2,2':6',2''-terpyridine]-4,4''-dicarboxylic acid (H₂PTP) and 4'-(pyridin-3-yl)-[2,2':6',2''-terpyridine]-4,4''-dicarboxylic acid (H₂MTP) as the ligands, respectively. Crystal structure analysis reveals that (II) possesses a 2D coordinated layer structure, in which adjacent 2D coordination layers are linked into 3D frameworks through π-π interactions, while the structure of (I) displays dual coordination layers, in which adjacent coordination layers are connected into a 3D framework through hydrogen-bonding interactions. The photophysical properties of the two MOFs were investigated by fluorescence spectroscopy. Complex (II) shows an obvious `turn-on' fluorescence enhancement effect towards flazasulfuron and its potential application for sensing flazasulfuron in water with high selectivity and sensitivity was also investigated in detail.