Story of Quinoline–Naphthalene-Embedded Coordination Polymers: Crystal Engineering, Food Spoilage Detection, and Integration with Smartphone Technologies

Crystal arrangements with versatile architectures can be developed by varying functionalization in structurally similar building components and exploring the significance of such networking, which remains a key focus of interest in the functional world of applied inorganic chemistry. In this context, we have introduced a series of novel coordination polymers (CPs), <b>SeCP-1</b>({[Cd(L1)(SeCN)₂]·0.5CHCl₃.0.75H₂O}<i>_n</i>), <b>SeCP-2</b>([Cd₂(L2)₂(SeCN)₃(NO₃)]<i>_n</i>), and <b>SeCP-3</b>({[Cd(L1)(L2)(SeCN)(NO₃)]·2.5H₂O}<i>_n</i>), featuring ligand versatility, keeping central metal ion and bridging ligand constant. Among these three quinoline-naphthalene-embedded CPs, <b>SeCP-1</b> and <b>SeCP-2</b> are constructed using L1 and L2 [L1 = (1-((<i>Z</i>)-((<i>Z</i>)-(quinolin-4-ylmethylene)hydrazono)methyl)naphthalen-2-ol) and L2 = ((1<i>E</i>,2<i>E</i>)-1,2-bis(quinolin-4-ylmethylene)hydrazine)] ligands, respectively, whereas <b>SeCP-3</b> is structured with both L1 and L2 ligands. The structural versatility of CPs is revealed by single-crystal X-ray diffraction, and their distinct features are explored by molecular spectroscopy. The enhanced photophysical properties of these CPs enable effective monitoring of volatile amines, key indicators of food spoilage. <b>SeCP-1</b> and <b>SeCP-3</b> show superior detection of aliphatic volatile amines in solid and solution phases at nanomolar levels, except <b>SeCP-2</b>. These molecularly designed CP-coated paper strips can be used to detect spoilage in rotten fish, counter-supported by spectroscopic and theoretical calculations. These strips can detect unsafe levels of amines by producing a colorimetric signal indicating spoilage. Signals are quantified using a smartphone and digital one-to-three decoder circuitry for on-site monitoring.