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• Three donor-acceptor compounds were designed and synthesized, and their structures were studied. • Compounds 1–3 exhibit photochromic properties and interesting photomodulated luminescence properties. • Compound 1 can be used as an ammonia vapor sensor. Synthesized three different supramolecular polymers, {[(4-BCBPY) 0.5 (H 2 BTEC) 0.5 ]·H 2 O} n (1), {[(4-BCBPY)(C 2 H 5 NO)C l ]·H 2 O} n (2) and {[(4-BCBPY)(C 2 H 5 NO)C l ]·H 2 O} n (3) (H 2 BTEC2− = 1,2,4,5-benzenetetracarboxylic acid anion). In compound 1 , benzene carboxylic acid anion acts as an electron donor, and electron-deficient viologen acts as an electron acceptor to form a supramolecular assembly. In compounds 2 and 3 , electron-deficient viologen forms supramolecular assemblies with N-methylformamide, water and chloride ions. All three compounds are connected through non-covalent interactions and form a donor-acceptor (D-A) system. Compounds 1, 2 and 3 all exhibited photochromic behavior of electron transfer, while also exhibiting interesting photomodulated luminescence behavior. And compound 1 can also be used as an ammonia vapor sensor material. The photochromic mechanism of the compound and the correlation between calculation and practice are deeply studied by using time-dependent density functional theory (TDDFT). [Display omitted] Three new supramolecular compounds {[(4-BCBPY) 0.5 (H 2 BTEC) 0.5 ]·H 2 O} n (1), {[(4-BCBPY)(C 2 H 5 NO)C l ]·H 2 O} n (2) and {[(4-BCBPY)(C 2 H 5 NO)C l ]·H 2 O} n (3) were synthesized using viologen ligands 4-BCBPY·2Cl (1,1′-bis(4-cyanobenzyl)-4,4′-bipyridinium dication) and H 4 BTEC as raw materials. The effects of metal salts and pH on the structures of the three compounds were studied. Under the irradiation of 350 W xenon lamp, the three compounds change from their original color to blue, which is caused by photo-generated viologen free radicals. Compounds 1, 2 and 3 also showed interesting photomodulated luminescence behavior. At the same time, compound 1 can be used as an ammonia vapor sensor. [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]

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]

Two novel cadmium viologen coordination polymers (CPs) {[Cd(BTC)(H 2 O)]·(Mebpy)} n (1) and {[Cd 1.5 (Mebpy)(BDC) 1.5 Cl]·(DMF)} n (2) were synthesized (Mebpy+ = N -methyl-4,4′-bipyridinium cation, DMF = N, N -Dimethylformamide, BTC3– = 1,3,5-benzenetricarboxylic acid anion and BDC4- = 1,4-dicarboxybenzene acid anion). The structures of two compounds were studied. For compound 1 , Cd2+ is bridged with BTC3- to form a 3D structure, and Mebpy+ cations are present in the channel of compound 1. In compound 2 , Cd2+, BDC2- and Mebpy+ form a 3D structure. And because of their different structures, they exhibit different properties. [Display omitted] • Two new coordination polymers (CPs) based on viologen ligands were synthesized. • 1,3,5-benzenetricarboxylic acid and 1,4-dicarboxybenzene acid ligands form different 3D structures. • The photochromic properties of the compounds were explored. Two novel cadmium viologen coordination polymers (CPs) {[Cd(BTC)(H 2 O)]·(Mebpy)} n (1) and {[Cd 1.5 (Mebpy)(BDC) 1.5 Cl]·(DMF)} n (2) (Mebpy+ = N -methyl-4,4′-bipyridinium cation, DMF = N, N -Dimethylformamide) were prepared in the reaction of CdCl 2 with different aromatic carboxylic acid ligands such as 1,3,5-benzenetricarboxylic acid (H 3 BTC) or 1,4-dicarboxybenzene acid (H 2 BDC) under hydrothermal conditions in the presence of N -carboxymethyl-4,4′-bipyridinium chloride (CEbpy·Cl). Single-crystal structure analysis revealed that the Cd(II) ions are bridged by BTC3- anions to form a 3D structure with the Mebpy+ cations occupying channel pores in compound 1 , while the metal ions are bridged by BDC2- and Cl- anions to form a 3D structure with Mebpy + cations in compound 2. Interestingly, it has been found that the structure of the two compounds depends on aromatic carboxylic acid ligands. Compounds 1 and 2 exhibit photochromic behavior under xenon lamp irradiation, accompanied by visible color changes from original color to blue. [ABSTRACT FROM AUTHOR]

• Two new compounds were synthesized. • These two compounds can be used to detect Cr 2 O 7 2−. • Compound 2 exhibits ammonia sensing properties. Two new Zn (II)-viologen chromic compounds, named {[(4-BCBPY) 0.5 (HIPA)]·H 2 O} n (1) and {[Zn 3 (IPA) 4 (4-BCBPY)]·2H 2 O} n (2) (4-BCBPY2+ = 1,1′-bis(4-cyanobenzyl)-4,4′-bipyridinium dication, H 2 IPA = isophthalic acid) have been synthesized through varying reaction conditions. Structural analysis reveals that compound 1 possesses a supramolecular compound, while compound 2 exhibits a metal-organic framework (MOF) structure built from trinuclear metal building units. Under the irradiation of a 300 W Xe lamp, compound 1 undergoes a color change from orange to brown, while compound 2 transitions from yellow to green. The introduction of metal ions in compound 2 enhances its light response rate compared to compound 1. Additionally, compound 2 displays a visible color change in the presence of ammonia, whereas compound 1 does not exhibit this capability. Meanwhile, the stable product 2P of 2 was obtained through irradiation, and the structural differences between 2 and 2P were analyzed. Furthermore, the study of time-dependent density functional theory (TDDFT) provides theoretical support for understanding the properties of 1 and 2. Both compounds exhibit intriguing photomodulated luminescence properties and demonstrate remarkable sensing abilities toward Cr 2 O 7 2−. Notably, the introduction of metal ions was found to modulate the photochromic behavior as well as the ammonia/anion sensing properties of these compounds. Two new chromic compounds named {[(4-BCBPY) 0.5 (HIPA)]·H 2 O} n (1) and {[Zn 3 (IPA) 4 (4-BCBPY)]·2H 2 O} n (2) were synthesized from 1, 1 '-bis (4-cyanobenzyl)-4, 4′-bipyridinium and 1, 3-phthalic acid. Compound 1 showed a color change from orange to brown under light irradiation, and the compound 2 showed a color change from yellow to green. The two compounds were used as fluorescence sensors for the detection of Cr 2 O 7 2−. It has good stability and low detection limit for Cr 2 O 7 2−. [Display omitted] [ABSTRACT FROM AUTHOR]

Three compounds based on bcbpy ligands were designed. These compounds have photochromic/ammonia properties, and the response rate is affected by intermolecular D-A distance, hydrogen bond and π-π interaction. Among them, 1 and 3 can be used for ammonia/Cr 2 O 7 2- anion detection and ink-free erasable printing, respectively. [Display omitted] • Three multi stimulus response compounds were designed and synthesized, and their structures were studied. • Compounds 1 – 3 showed discoloration to light and ammonia vapor. • Compound 1 can be used as ammonia vapor and Cr 2 O 7 2- anion sensor. • Compound 3 can be applied in the field of ink-free erasable printing. Three new compounds {[(bcbpy) 2 ]·10H 2 O} n (1), {[(H 2 bcbpy)(H 2 btec)(NaOH)(H 2 O)]·H 2 O} n (2), {Cd(bcbpy) 0.5 (btec) 0.5 (H 2 O)} n (3) were synthesized under hydrothermal conditions in the presence of viologen 1,1′-bis (3-carboxybenzyl)-4,4′-bipyridinium dichloride (H 2 bcbpy·2Cl), 1,2,4,5-Benzenetetracarboxylic acid (H 4 btec) and different metal salts. Interestingly, it has been found that the structure of the three compounds depends on metal salts. All three compounds exhibited photochromic properties under the irradiation of a 300 W xenon lamp, compound 1 changed from yellow to dark green, compound 2 changed from light yellow to blue, and compound 3 changed from light gray to blue. Due to the influence of intermolecular D-A distance, π-π interaction, intermolecular hydrogen bond and metal ions, there are sensing differences among the three compounds, and their light response rates are 1 > 2 > 3. It is worth noting that all three compounds produce color changes under ammonia vapor, and the fluorescence quenching effect of compound 1 can also be observed under the action of Cr 2 O 7 2- anion. [ABSTRACT FROM AUTHOR]

The two coordination polymers have good reversible photochromic properties and ammonia sensing properties. Complexes 1 and 2 exhibit a difference in sensing, with a response rate of 2 > 1 to light. [Display omitted] • Two metal coordination polymers were designed and synthesized, and their structures were studied. • Complexes 1 and 2 both exhibit stimuli-responsive properties to light, have photochromic properties. • Complexes 1 and 2 are sensitive to ammonia vapor and can be further explored in the field of ammonia sensing. Synthesized two supramolecular coordination polymers, {Cd 3 [(bcbpy) 3 Cl 6 ]·8H 2 O} n (1) (bcbpy = 1,1′-bis(3-carboxybenzyl)-4,4′-bipyridinium) and {Zn[(bcbpy) 0.5 (nip)]·H 2 O} 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. [ABSTRACT FROM AUTHOR]