Two new multi-functional coordination polymers exhibiting photochromic behavior and amine-selective sensing capability

The self-assembly of Cd(II) ions with two kind of viologen ligands 1-(3,5-dicarboxybenzyl)-4,4′-bipyridinium chloride (H2L1+Cl−), 1-(3-carboxybenzyl)-4,4′-bipyridinium chloride (HL2+Cl−) and 1,3,5-benzenetricarboxylic acid (H3BTC) under solvothermal and hydrothermal conditions results in two coordination polymers, namely, {[Cd(L1)OH]}n (1) and {[Cd(L2)(HBTC)H2O]·2H2O}n (2). Due to the formation of viologen radicals, they exhibit reversible photochromism through electron transfer, and the order of light response time is 2 > 1. The time-dependent density functional theory (TDDFT)-B3LYP/lanl2dz method was used to deeply understand the donor–acceptor structures, the matching rules between L and acid parts, and the intermolecular/intramolecular atom- atom close contact based on the fraction of intercontact. Compound 1 exhibit intramolecular electron transfer. Compound 2 exhibits two electron transfer modes: intramolecular and intermolecular electron transfer. In addition, when exposed to various amines (NH3, TEA = triethylamine, MA = o-methylaniline, aniline), compound 1 displays significantly different visual color changes.