Two New Coordination Polymers Based on Viologen Ligands: Synthesis, Photochromism and Ammonia Sensing

Synthesized two supramolecular coordination polymers, {Cd3[(bcbpy)3Cl6]·8H2O}n (1) (bcbpy = 1,1′-bis(3-carboxybenzyl)-4,4′-bipyridinium) and {Zn[(bcbpy)0.5(nip)]·H2O}n (2) (nip2- = 5-nitroisophthalic acid anion), showed good photochromic properties when both coordination polymers changed from yellow to dark green under light stimulation, and the primary color could be restored at 85–95 °C for 60 min, this reversible cycle can be repeated more than 5 times. This photochromism is caused by photoinduced electron transfer to viologen free radicals. In addition, in ammonia vapor, both complexes changed from yellow to tan, showing good ammonia sensing characteristics. Research has found that complexes 1 and 2 exhibit sensing differences, with a response rate to light of 2 > 1. This sensing difference is mainly related to the D-A distance between molecules, π-π interactions, and the regulatory effect of metal ions or secondary ligands.