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Three compounds were synthesized and characterized based on the same viologen ligand and different metal salts. Although their range of applications is basically similar, their different internal structures result in different light response rates. [Display omitted] • Three new multifunctional viologen coordination polymers have been synthesized. • Three compounds all exhibit high sensitivity to UV light. • In the process of detecting ammonia, the three compounds showed excellent stimulus response ability. • The ability of the three compounds to detect different concentrations of Cr 2 O 7 2-anions was further verified by fluorescence quenching effect. Three Zn/Cd-viologen coordination polymers (CPs), namely, {Zn[(bcbpy) 0.5 (ipa)(H 2 O)]·H 2 O} n (1), {Zn[(bcbpy) 0.5 (ipa)(H 2 O) 0.5 ]·H 2 O} n (2), and {Cd[(bcbpy)(SO 4)]·2H 2 O} n (3), have been constructed using aromatic carboxylic acid and viologen-derived ligands, where H 2 bcbpy·2Cl represents 1,1′-bis((4-carboxyphenyl)-4,4′-bipyridine) dichloride and H 2 ipa stands for isophthalic acid. All three CPs display photochromic properties, transforming from yellow to dark blue upon irradiation with a xenon lamp. Notably, the photoresponse rates vary among these CPs, with compound 1 showing the fastest photoresponse, followed closely by compounds 2 and 3. Furthermore, CPs 1 , 2 , and 3 display a unique sensitivity to different concentrations of Cr 2 O 7 2- anion solutions. When immersed in these solutions, the compounds exhibit varying degrees of fluorescence quenching effects, allowing for the monitoring of even the lowest ion concentrations. Additionally, upon exposure to ammonia vapor, the three compounds undergo a color change from yellow to dark brown, indicating their sensitivity to ammonia vapor. [ABSTRACT FROM AUTHOR]

Compounds 1 and 2 were synthesized and characterized based on different viologen ligands. They showed different structures, photochromism and applications. [Display omitted] • Two novel multifunctional Cd-viologen coordination polymers have been synthesized. • Compounds 1 and 2 exhibit high sensitivity to UV light. • Compound 2 has the ability to detect amines. The self-assembly of Cd(II) ions with two kind of viologen ligands 1-(3,5-dicarboxybenzyl)-4,4′-bipyridinium chloride (H 2 L1+Cl −), 1-(3-carboxybenzyl)-4,4′-bipyridinium chloride (HL2+Cl −) and 1,3,5-benzenetricarboxylic acid (H 3 BTC) under solvothermal and hydrothermal conditions results in two coordination polymers, namely, {[Cd(L1)OH]} n (1) and {[Cd(L2)(HBTC)H 2 O]·2H 2 O} 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 (NH 3 , TEA = triethylamine, MA = o-methylaniline, aniline), compound 1 displays significantly different visual color changes. [ABSTRACT FROM AUTHOR]