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Two novel 1D Cd‐based coordination polymers (CPs) {[Cd(MQ)(HBTC)(H2O)2] ⋅ (H2BTC) ⋅ 4H2O}n (1) and {[Cd(AQ)(HBTC)(H2O)Br] ⋅ 2H2O}n (2) have been prepared in the reaction of Cd2+ with different viologen ligands such as 1‐methyl‐4,4′‐bipyridinium bromide (MQBr) or 1‐amyl‐4,4′‐bipyridinium bromide (AQBr) in the presence of 1,3,5‐benzenetricarboxylic acid (H3BTC). The Cd2+ ions are bridged by HBTC2− anions to take shape a 1D configuration for two CPs. Additionally, 1 and 2 both show photochromism due to the photoinduced electron transfer (ET) from electron‐rich O atoms to electron‐deficient viologen moieties. Compared with 2, compound 1 has a rapid photoresponsive rate. The different photochromic behaviors have been discussed adequately. [ABSTRACT FROM AUTHOR]

Selecting different metal ions, two novel complexes {[Zn(BCbpy)(m‐BDC)(H2O)] ⋅ 2H2O}n (1) and [Co(H2O)6]0.5[Co0.5(BCbpy)(H2O)2](m‐BDC) ⋅ 3H2O ⋅ DMF (2) have been prepared and structurally characterized in the presence of the viologen ligand 1‐(4‐carboxybenzyl)‐4,4′‐bipyridinium (BCbpy) and 1,3‐benzenedicarboxylic acid (m‐H2BDC). The crystal structures and photochromic properties of two complexes have been investigated in this article. 1 possesses a two‐dimensional (2D) layered structure, while the structure of 2 is zero‐dimensional (0D). As expected, 1 and 2 were discovered to be photochromic accompanying electron transfer (ET). Interestingly, 1 can be dissolved in ethanol solution and deposited on filter paper, applied to a printing medium without ink. [ABSTRACT FROM AUTHOR]

• Three novel cocrystals synthesized from BCMbpy and various acids were developed. • The cocrystals exhibit reversible ET photochromic behavior. • Compound 3 demonstrates both intramolecular and intermolecular ET modes, with the fastest photoinduced color change response. • UV–vis and EPR spectra confirm the formation of viologen radicals upon irradiation. Three cocrystals synthesized from 1,1′-bis(carboxymethyl)-4,4′-bipyridine (BCMbpy) have been developed: (H 2 BCMbpy) 0.5 (H 2 BTEC) 0.5 ·(H 4 BTEC) 0.5 ·2H 2 O (1), (BCMbpy) 0.5 ·(H 2 TPDC)·H 2 O (2), and (BCMbpy)·(H 4 BTEC)·2H 2 O (3) (where H 4 BTEC is 1,2,4,5-benzenetetracarboxylic acid and H 2 TPDC is thiophene-2,5-dicarboxylic acid). The crystal structures and photochromic properties of the three cocrystals were investigated. All three compounds exhibit reversible electron transfer (ET) photochromic behavior, reverting to their original colors in darkness. Notably, compound 3 demonstrates both intramolecular and intermolecular ET modes. The response rates for photoinduced color changes are ranked as 3 > 1 > 2 , which is influenced by the steric and electronic structures of the compounds. This indicates that the balance between ET and resultant photochromism can be achieved through the careful modulation of electron acceptors and donors. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Two Mn(II) and Cd(II) complexes were constructed and characterized. • Compound 2 exhibits excellent photochromic property. • Compound 2 shows electron transfer from 1,2,4-BTC3- anion towards bipyridinium component. This study investigates the crystal structures and photochromic properties of two viologen-based compounds [Mn(CMbpy)(BTEC) 0.5 (H 2 O) 4 ]·0.5(H 2 BTEC)·3H 2 O (1) and [Cd(CMbpy)(1,2,4-BTC)(H 2 O)] n (2) [CMbpyBr = 1-(1-cyclohexylmethane)-4,4′-bipyridinium bromide, H 4 BTEC=1,2,4,5-benzenetetracarboxylic acid, 1,2,4-H 3 BTC=1,2,4-benzenetricarboxylic acid]. X-ray diffraction analysis identified compound 1 as a triclinic ionic lattice featuring Mn(II) in an octahedral coordination with CMbpy cations, whereas compound 2 crystallizes in an orthorhombic space group forming a three-dimensional MOF stabilized by CMbpy cations. Compound 1 demonstrated no color change, while compound 2 exhibited a rapid transition to a blue state upon UV irradiation, with an accompanying emergence of new absorption peaks, indicative of viologen radical formation. This behavior was corroborated by electron paramagnetic resonance (EPR) spectroscopy. Our findings provide a profound understanding of the structure–function relationship in these viologen complexes, highlighting the synergy between metal coordination, hydrogen bonding, and the strategic positioning of donor–acceptor components. [ABSTRACT FROM AUTHOR]

Three Mn–viologen complexes containing 1-carboxyethyl-4,4′-bipyridinium (CEbpy) were synthesized, [Mn(H2O)6]·2(CEbpy)·(TPDC)·3H2O (1), [Mn(H2O)6]·2(CEbpy)·(m-BDC)·2H2O (2) and [Mn(H2O)6]·2(CEbpy)·(p-BDC)·2H2O (3) (H2TPDC = thiophene-2,5-dicarboxylic acid, m-H2BDC = 1,3-benzenedicarboxylic acid, p-H2BDC = 1,4-benzenedicarboxylic acid), which were investigated based on crystal structures, photochromism, molecular orbitals, Hirshfeld surfaces and 2D fingerprint plots. All three complexes present sensitive photoresponse behaviors in the sequence of 1 ≫; 3 > 2, due to the existence of electron-deficient viologen fractions. Compound 1 exhibits two electron transfer modes: intramolecular and intermolecular electron transfer. Compounds 2 and 3 exhibit intramolecular electron transfer. The density functional theory (DFT)-B3LYP/6-311(d,p) method was used to gain insight into the donor–acceptor structures, matching rules between CEbpy and the acid moiety as well as inter/intramolecular atom–atom close contacts based on the fraction of intercontact. [ABSTRACT FROM AUTHOR]

Based on a bipyridinium carboxylate ligand 1,1′-bis(3-carboxylatobenzyl)-(4,4′-bipyridinium)-dichloride (H2bcbpyCl2), three new coordination polymers {[Co0.5(bcbpy)0.5(H2O)2](p-BDC)0.5·H2O}n (1) {[Ni(bcbpy)(H2O)4](p-BDC)·2H2O}n (2) and [Zn2(bcbpy)(BTEC)(H2O)2·6H2O]n (3) are designed and synthesized by varying the benzenecarboxylic acids (1,4-benzenedicarboxylic acid = p-H2BDC, 1,2,4,5-benzenetetracarboxylic acid = H4BTEC) to adjust the coordination mode between the viologen ligand and metal ions. Single crystal structure analyses reveal that compounds 1 and 2 both exhibit one-dimensional (1D) chain-like structure, while compound 3 exhibits two-dimensional (2D) layered architecture. Furthermore, due to the formation of viologen radicals, reversible color changes for three compounds can be observed in the air upon sunlight, UV-light and X-ray irradiation. Particularly, compound 3 has high photosensitivity, giving an eye-detectable color change after exposure to sunlight in air within 1 min. In addition, the photoproducts for the three compounds exhibit an ultralonglived charge-separated state. [ABSTRACT FROM AUTHOR]

Abstract: The self‐assembly reaction of TM(NO3)2 (TM=Co, Ni), benzenedicarboxylic acid (H2BDC), and ethyl viologen cations leads to two novel host‐guest compounds (EV)[Co(H2O)6](p‐BDC)2⋅4H2O (1) and {(EV)[Ni3(m‐BDC)4]}n (2), (p‐H2BDC=1,4‐benzenedicarboxylic acid, m‐H2BDC=1,3‐benzenedicarboxylic acid, EV2+=1,1’‐bis(ethyl)‐4,4’‐bipyridinium dication). Compound 1 is a host‐guest supramolecule consisting of one EV2+ cation, one [Co(H2O)6]2+ cation, two uncoordinated deprotonated p‐BDC2− anions and four free H2O molecules, which exhibits electron‐transfer (ET) photochromism and thermochromism through dehydration and rehydration. Furthermore, 1 can exhibit a secondary ET photochromism after thermal stimuli. Compound 2 is constructed by the combination of ethyl viologen guest molecule and a highly stable [Ni3(m‐BDC)4]n host MOF, displaying both photo‐ and thermo‐induced electron transfer reaction. The different packing modes of the donor and acceptor blocks between 1 and 2 lead to the different chromic properties. [ABSTRACT FROM AUTHOR]

Three novel viologen donor–acceptor (D–A) supramolecules have been got, all displaying electron transfer photochromism. [Display omitted] • Three D–A supramolecules based on the viologen moiey have been got. • Their crystal structures and photochromic properties have been studied. • At the same time, the fluorescent characteristics and ink-free erasable printing properties are also discussed. Based on different proton-deprived benzenecarboxylic acids (H 2 TPDC = thiophene-2,5-dicarboxylic acid, 1,4-benzenedicarboxylic acid = p -H 2 BDC, 1,2,4,5-benzenetetracarboxylic acid = H 4 BTEC) as electron donors and the cationic viologen derivative 1,1′-bis(3-carboxylatobenzyl)-4,4′-bipyridinium (H 2 bcbpy2+) as the electron acceptor, three novel donor–acceptor (D–A) supramolecules (H 2 bcbpy)(TPDC) . 5.5H 2 O (1), (H 2 bcbpy)(BDC)·2H 2 O (2) and (H 2 bcbpy)(H 2 BTEC)·3H 2 O (3) have been prepared. Their crystal structures and photochromic properties have been studied. As expected, three compounds are found to have electron transfer (ET) photochromism with fluorescent characteristics and ink-free erasable printing properties. [ABSTRACT FROM AUTHOR]

Three complexes possess similar basic building block, but show different resultant constructions and photochromic properties. [Display omitted] • Three novel complexes have been obtained based on the 1-(1-cyclohexylmethane)-4,4′-bipyridinium ligand. • Their crystal structures and photochromic properties have been studied. • The relationship between structure and photosensitivity has been discussed. In order to study how molecular packing affects photochromic performance, three secondary building linkers are introduced into the bipyridinium-based complexes, namely, Zn(CMbpy)(p -BDC) 0.5 (p -HBDC)Br·2H 2 O (1), [Zn(CMbpy)(m -BDC)(m -HBDC)·3H 2 O] n (2), [Zn(CMbpy)(BTEC) 0.5 (H 2 BTEC) 0.5 ·2H 2 O] n (3) (p -H 2 BDC = 1,4-benzenedicarboxylic acid, m -H 2 BDC = 1,3-benzenedicarboxylic acid, H 4 BTEC = 1,2,4,5-benzenetetracarboxylic acid, CMbpyBr = 1-(1-cyclohexylmethane)-4,4′-bipyridinium bromide). These three complexes possess similar basic building block, but show different resultant constructions. Complex 1 is isolated, complex 2 features one-dimensional chain-like structure, while complex 3 has a two-dimensional layered structure. Upon UV illumination, complexes 1–3 display photochromic behaviors originating from photo-induced electron transfer process. The relationship between structure and photosensitivity has been discussed. [ABSTRACT FROM AUTHOR]

Three compounds show metal-dependent chromic behaviors and different adjustable responsive characteristics. • Three novel complexes have been got based on the new viologen 1-(4-carboxybutyl)-4,4′-bipyridinium ligand. • Their crystal structures and chromic properties have been studied. • Metal ions can effectively control their photochromic properties. In this work, three novel isolated complexes derived from a new viologen ligand 1-(4-carboxybutyl)-4,4′-bipyridinium bromide (HCPbpyBr) have been prepared [Co(HCPbpy)(H 2 O) 5 ]·(BTC)·5·.5H 2 O (1), [Ni(HCPbpy)(H 2 O) 5 ]·(BTC)·5·.5H 2 O (2), [Zn(HCPbpy)(BTEC) 0.5 (H 2 O) 4 ]·(H 2 BTEC) 0.5 ·3H 2 O (3) (H 3 BTC = 1,3,5-benzenetricarboxylic acid; H 4 BTEC = 1,2,4,5-benzenetetracarboxylic acid). Their crystal structures and chromic behaviors are also explored. Complexes 1 and 2 own the same structure and exhibit hydrochromism due to the d-d transition in the ligand field observed by dehydration and rehydration. In addition, complex 2 is photochromic as the result of the generation of viologen radicals, while complex 1 is non-photochromic even after exposure to UV light for a long period of time. Similar to 2 , complex 3 exhibits obvious photochromic behavior upon UV irradiation. The different chromic behaviors of these three complexes have been discussed. [ABSTRACT FROM AUTHOR]

In this work, a neutral viologen derivative, N,N′-bis(carboxyethyl)-4,4′-bipyridinium (BCEbpy), has been selected as the main ligand, and 1,3,5-benzenetricarboxylic acid (H 3 BTC) as the auxiliary ligand to construct three novel coordination polymers {Zn 1.5 (BCEbpy) 0.5 (BTC)(H 2 O) 3 ·3H 2 O} n (1) {Cd 1.5 (BCEbpy) 0.5 (BTC)(H 2 O)·3H 2 O} n (2), {Mn 1.5 (BCEbpy) 0.5 (BTC)(H 2 O)·3H 2 O} n (3) by varying different metal ions. Complex 1 features the 2D layered architecture, while complexes 2 and 3 have the same 3D framework. The difference in the structures of the three complexes is due to the different coordination ability of metal ions. The photochromic properties of these three complexes have also been investigated, only complexes 1 and 2 show color changes upon UV irradiation. The effect of metal ions on the photochromic behavior has been discussed. Image 1 • Three novel coordination polymers have been got by varying different metal ions. • Their crystal structures and photochromic properties have been studied. • Metal ions not only affect the geometry, but also can effectively control the photochromic property. [ABSTRACT FROM AUTHOR]

The different chromic properties of 1 – 3 should be related to different metal ions and the accompanying differences in the interaction between the acceptor and donor. • Three novel complexes have been obtained based on the viologen 1-(1-cyclohexylmethane)-4,4′-bipyridinium ligand. • Their crystal structures and chromic properties have been studied. • Metal ions can effectively affect their chromic properties. The viologen moiety has been widely used to endow complexes with chromic properties. In this work, we report three complexes Co(CMbpy)(H 2 O) 5 ·BTC (1), Ni(CMbpy)(BTC)(H 2 O) 4 ·5H 2 O (2), [Zn(CMbpy)(HBTC)(H 2 O)·(H 2 BTC)·3H 2 O] n (3) based on a viologen-derived ligand 1-(1-cyclohexylmethane)-4,4′-bipyridinium bromide (CMbpyBr) and 1,3,5-benzenetricarboxylic acid (H 3 BTC) by varying different metal ions, which endow these complexes with different structures and chromic properties. Of the three complexes, only 3 exhibits photochromism due to the generation of viologen radicals by photoinduced electron transfer. The reason why 1 and 2 cannot perform photochromism can be related to the slightly longer ET distance and the weaker electron-withdrawing ability of Co(II) and Ni(II). In contrast, complexes 1 and 2 exhibit irreversible hydrochromism due to the d-d transition in the ligand field observed by dehydration. This work provides new strategies for developing different responsive materials. [ABSTRACT FROM AUTHOR]

A new viologen ligand 1-(1-cyclohexylmethane)-4,4′-bipyridinium bromide (CMbpyBr) in the presence of benzenecarboxylates and metal ions affords three coordination polymers [Zn(CMbpy)(HBTC)Br] n (1), [Cd(CMbpy)(m -BTC)(H 2 O)] n (2) and {[Cd(CMbpy)(m -BDC)(H 2 O) 2 [Cd(m -BDC)(m -HBDC)(H 2 O)]} n (3) (H 3 BTC = 1,3,5-benzenetricarboxylic acid, m -H 3 BTC = 1,2,4-benzenetricarboxylic acid, m -H 2 BDC = 1,3-benzenedicarboxylic acid). Compounds 1 and 3 both have 1D structures, while compound 2 is 3D structure. More importantly, three compounds exhibit excellent photochromic behaviors in response to UV and X-ray dual light due to the formation of viologen radicals. However, the decolorization of the photochromic products for the three compounds is very different. The reason for their different photochromic behaviors has been explored. Image 1 • A new viologen ligand has been used to construct CPs. • Their crystal structures and photochromic properties have been studied. • Three CPs exhibit excellent photochromic behaviors in response to UV and X-ray dual light. [ABSTRACT FROM AUTHOR]

Based on different benzenecarboxylic acids (H 3 BTC = 1,3,5-benzenetricarboxylic acid; H 4 BTEC = 1,2,4,5-benzenetetracarboxylic acid; m -H 3 BTC = 1,2,4-benzenetricarboxylic acid) and viologen cations (BV2+ = 1,1′-bis(butyl)-4,4′-bipyridinium dication; AV2+ = 1,1′-bis(amyl)-4,4′-bipyridinium dication; HV2+ = 1,1′-bis(hexyl)-4,4′-bipyridinium dication), five novel supramolecular assemblies (BV)(H 2 BTC) 2 (H 3 BTC) 2 (1), [(BV) 0.5 (H 3 BTEC)]·H 2 O (2), (BV) 0.5 (m -H 2 BTC) (3), (AV) 0.5 (m -H 2 BTC) (4), (HV) 0.5 (m -H 2 BTC) (5) have been prepared. The electron-deficient viologen groups and the electron-donating benzenecarboxylate units are hydrogen-bonded to form the donor-acceptor (D–A) system. Under light illumination, photoactivated electrons can be transferred from the donor to the acceptor units in compounds 2 – 5. Their different photoactive properties can be attributed to the alkyl groups introduced, packing and valence of the functional D–A moieties. Image 1 • Based on different benzenecarboxylic acids and viologen cations, five novel supramolecules have been prepared. • Their crystal structures and photochromic properties have been studied. • The introduction of hexyl group on viologens can significantly enhance the photosensitivity. [ABSTRACT FROM AUTHOR]

Three novel coordination polymers (CPs) based on 1-(2-carboxyethyl)-4,4′-bipyridinium bromide (HCBbpyBr) have been prepared {[Cd 2 (CBbpy)(m -BDC) 2 (H 2 O) 4 ]·H 2 O} n (1), {[Ni(CBbpy) 2 (H 2 O) 2 ](p -BDC)·6H 2 O} n (2), {[Co(CBbpy) 2 (H 2 O) 2 ](p -HBDC) 2 ·3H 2 O} n (3) (m -H 2 BDC = 1,3-benzenedicarboxylic acid; p -H 2 BDC = 1,4-benzenedicarboxylic acid). The crystal structures and chromic behaviors of three compounds have been studied. Single-crystal X-ray analyses reveal that compound 1 features a 2D-layered structure, compounds 2 and 3 have similar 1D double chain-like structure. Compound 1 displays electron-transfer (ET) photochromism, compound 2 exhibits ligand-based ET photochromism and metal-based hydrochromism owing to ligand-field change induced by de-/rehydration, while compound 3 exhibits ET thermochromism accompanying ligand-field change around the metal. The differences in the central metal ions and auxiliary carboxylate units have a great influence on the final structures, and further result in their different chromic behaviors. Image 1 • Three novel coordination polymers based on CBbpy ligand have been synthesized. • Three polymers display different chromic behaviors. • The differences in the central metal ions and auxiliary carboxylate ligands have a great influence on the chromism. [ABSTRACT FROM AUTHOR]

Herein, four compounds containing the neutral viologen derivative, 1-(2-carboxyethyl)-4,4′-bipyridine (CBbpy) have been synthesized, (CBbpy)·(H 2 TPDC)·H 2 O (1), [Co 0.5 (CBbpy)(H 2 O) 2 ](HTPDC)·2 H 2 O (2), [Ni 0.5 (CBbpy)(H 2 O) 2 ](HTPDC)·2 H 2 O (3) and {[Cd(CBbpy) 2 (H 2 O) 2 ][Cd(TPDC) 2 ]·4 H 2 O} n (4) (H 2 TPDC = thiophene-2,5-dicarboxylic acid). Compound 1 is a co-crystal that forms the donor-acceptor (D-A) system through non-covalent interactions. Compounds 2 and 3 own the same isolated structure, in which metal ions coordinate with CBbpy to form cations, while H 2 TPDC loses a proton to form anions. Compound 4 contains one-dimensional (1D) {[Cd(CBbpy) 2 (H 2 O) 2 ]2+} n double chain and two-dimensional (2D) {[Cd(TPDC) 2 ]2-} n layer, which leads to a 1D + 2D→three-dimensional (3D) interdigitated supramolecular architecture. Although four compounds comprise the same bipyridinium moiety, their chromic behaviors are different. Compounds 1 and 4 own reversible photochromic action, while 2 and 3 reveal hydrochromic action upon heating. Based on the photochromic properties of 1 and 4 , the photo-modulated fluorescence and the potential applications of inkless and erasable printing are investigated. [Display omitted] • Four compounds have been successfully prepared by utilizing the 1-(2-carboxyethyl)-4,4′-bipyridine (CBbpy) viologen ligand. • Compounds 1 and 4 own reversible photochromic action, while 2 and 3 reveal hydrochromic action upon heating. • The photo-modulated fluorescence and the inkless erasable printing capability are investigated. [ABSTRACT FROM AUTHOR]

• Three compounds containing 1-carboxyethyl-4,4′-bipyridine have been synthesized. • Compounds 1 and 3 exhibit photochromism, while 2 reveals hydrochromism upon heating. • Photo-controlled fluorescence and ink-free erasable printing abilities are discussed. Herein, three compounds containing the neutral viologen derivative, 1-carboxyethyl-4,4′-bipyridine (CEbpy) have been synthesized, (CEbpy)·(H 2 TPDC)·2H 2 O (1) [Co(CEbpy)(TPDC)(H 2 O) 4 ]·3H 2 O (2) and [Cd 3 (CEbpy) 2 (TPDC) 3 ·7H 2 O] n (3) (H 2 TPDC = thiophene-2,5-dicarboxylic acid). Compound 1 is a supramolecular assembly, linked by non-covalent interactions to constitute the donor-acceptor (D-A) system. Compound 2 owns a zero-dimensional (0D) isolated structure in which metal ions are coordinated with CEbpy and fully deprotonated (TPDC)2- ligands. Compound 3 exhibits a three-dimensional (3D) framework of trinuclear metal clusters, where each metal atom forms its own distinct linear one-dimensional (1D) chain along a specific axis. Although the three compounds comprise the same bipyridinium moiety and aromatic acid, their chromic behaviors are different. Compounds 1 and 3 exhibit reversible photochromism, while 2 reveals hydrochromism upon heating. Additionally, photo-modulated fluorescence as well as their potential applications in inkless erasable printing have been studied. [Display omitted] [ABSTRACT FROM AUTHOR]

The insertion of conjugated units between the two pyridine rings of traditional viologens is an effective way to regulate the stimulus response. Herein, the rigid thiazolothiazole extended viologen moiety (TTVP, 2,5-bis (pyridinium-4-yl) thiazolo [5,4- d ] thiazole propionate) has been utilized in the preparation of photochromic materials, in which two novel complexes {[Zn (TTVP) 0.5 (m -HBTC) (H 2 O)]·DMF·3H 2 O} n (1) and [Zn(H 2 O) 6 ] 0.5 (p -BDC) 0.5 ·(TTVP) 0.5 (2) (m -H 3 BTC = 1,2,4-benzenetricarboxylic acid, p -H 2 BDC = 1,4-benzenedicarboxylic acid), have been synthesized and characterized. Structural analysis exhibits that complex 1 features one-dimensional (1D) chain structure, while complex 2 exists as a discrete monomeric structure. As anticipated, both complexes exhibit reversible photochromic properties under UV irradiation because of electron transfer (ET). More importantly, the photo-controlled luminescent properties and the potential application as inkless and erasable printing media are also explored. [Display omitted] • The rigid thiazolothiazole extended viologen moiety has been utilized to prepare two photochromic complexes. • PH plays a crucial role in the synthesis process. • The photo-controlled luminescence and the potential application as inkless and erasable printing media are explored. [ABSTRACT FROM AUTHOR]

The photosensitivity of the compounds should be due to the rational modulation of electron acceptors and donors. [Display omitted] Two novel Mn(II)-based one-dimensional coordination polymers {[Mn(bcbpy)(H 2 O) 4 ]·(p -BDC)·2H 2 O} n (1) and {(bcbpy)·[Mn(NDC)(H 2 O) 4 ]·DMF·3H 2 O} n (2) constructed from the viologen moiety (1,1′-bis(3-carboxylatobenzyl)-4,4′-bipyridinium = bcbpy) and different aromatic dicarboxylic acids (p -phthalic acid = p -H 2 BDC, 1,4-naphthalene dicarboxylic acid = H 2 NDC), have been synthesized by solvent evaporation and characterized systematically. Their crystal structures and photochromic behaviors are investigated. Both complexes exhibit reversible photochromism due to forming viologen radicals through electron transfer. Meanwhile, photo-controlled fluorescence and ink-free erasable printing capabilities are discussed to enrich the research on crystal photophysical properties. [ABSTRACT FROM AUTHOR]

• Based on the viologen moiety and different benzenecarboxylic acids, four novel supramolecules have been prepared. • Their crystal structures and photochromic properties have been studied. • In addition, the photo-controlled fluorescence and the inkless and erasable printing capabilities are studied. Donor-acceptor (D-A) photochromic materials have attracted extensive attention due to their broad application prospects. Herein, based on the viologen moiety (Bcbpy = 1-(4-carboxybenzyl)-4,4′-bipyridinium) and different benzenecarboxylic acids (H 3 BTC = 1,3,5-benzenetricarboxylic acid; m -H 3 BTC = 1,2,4-benzenetricarboxylic acid; H 4 BTEC = 1,2,4,5-benzenetetracarboxylic acid; 1,4-H 2 NDC = 1,4-naphthalenedicarboxylic acid), four novel supramolecules have been prepared, namely (H 2 Bcbpy)(H 2 BTC) 2 ·(H 3 BTC)·H 2 O (1), (HBcbpy)(m -H 2 BTC)·2H 2 O (2), (HBcbpy)(H 2 BTEC) 0.5 ·3H 2 O (3), (HBcbpy)(1,4-HNDC) (4). The D -A system is formed by hydrogen bonding between the electron-deficient viologen acceptor and the electron-donating benzenecarboxylate donors. After UV irradiation, the photo-activated electrons can transfer from D to A in four compounds, exhibiting obvious photochromic behaviors. In addition, the photo-controlled fluorescence and the inkless and erasable printing capabilities are studied. [Display omitted] [ABSTRACT FROM AUTHOR]

Expanding the π-conjugated structure of traditional viologens by incorporating thiazole units to the bipyridine skeleton has attracted more and more attention. In this work, a rigid thiazolothiazole extended viologen ligand (TTVP, 2,5-bis (pyridinium-4-yl) thiazolo [5,4- d ] thiazole propionate) has been used to constitute three new functional Cd(II) coordination polymers (CPs), {[Cd(TTVP) 0.5 (HBTC)(H 2 O) 2 ]·2H 2 O} n (1), {[Cd(TTVP) 0.5 (p -BDC) 0.5 (p -HBDC)(H 2 O)]·3H 2 O} n (2), {[Cd(TTVP) 0.5 (m -BDC)]} n (3) by introducing different benzenecarboxylic acids as auxiliary ligands (H 3 BTC = 1,3,5-benzenetricarboxylic acid; p -H 2 BDC = 1,4-benzenedicarboxylic acid; m -H 2 BDC = 1,3-benzenedicarboxylic acid). The crystal structures and photochromic capabilities of 1 − 3 are studied. Both compounds 1 and 2 own one-dimensional (1D) chain-like structure, while compound 3 owns two-dimensional (2D) layered structure. As expected, compounds 1 − 3 show reversible photochromism due to electron-transfer (ET). In addition, the photo-controlled luminescent properties and the potential application as inkless and erasable printing media are also explored. [Display omitted] • Three functional Cd(II)-based CPs based on TTVP and different benzenecarboxylic acids have been synthesized. • Three CPs own obvious photochromic property due to electron transfer. • In addition, the photo-controlled luminescent properties and the potential application as inkless and erasable printing media have been explored. [ABSTRACT FROM AUTHOR]

[Display omitted] Based on the viologen ligand 1-(4-carboxybutyl)-4,4′-bipyridinium bromide (HCPbpyBr), three new complexes with different auxiliary ligands and metal ions have been prepared and structurally characterized, namely Ni(CPbpy)(H 4 BTEC) 0.5 (H 2 O) 4 ·(BTEC) 0.5 ·2H 2 O (1), Co(CPbpy)(H 4 BTEC) 0.5 (H 2 O) 4 ·(BTEC) 0.5 ·2H 2 O (2) and [Cd(CPbpy)(m -BDC)·2H 2 O] n (3) (1,2,4,5-benzenetetracarboxylic acid = H 4 BTEC, 1,3-benzenedicarboxylic acid = m -H 2 BDC). Complexes 1 and 2 have identical isolated structure, while complex 3 features a three-dimensional (3D) framework. Meanwhile, complex 3 exhibits electron-transfer (ET) UV and X-ray dual photochromism and photo-controlled luminescent properties, while photochromism is not observed in complexes 1 and 2. Additionally, complex 3 has the prospective application as an inkless and erasable printing material because of its excellent photochromic property. [ABSTRACT FROM AUTHOR]

In the last few years, more and more attention has been paid to the application of chromic materials, and photo-active viologen groups have been broadly assembled into functional materials with photochromism. However, the limited research conducted to date indicates that the extended viologen photochromic compounds are rarely reported. Herein, a rigid thiazolothiazole extended viologen moiety H 2 TTVPCl 2 (2,5-bis (pyridinium-4-yl) thiazolo [5,4- d ] thiazole propionate dichloride) is selected to construct two novel photochromic compounds, namely {[Zn(TTVP) 0.5 (BTEC) 0.5 (H 2 O) 2 ]·2H 2 O} n (1) and [(H 2 TTVP)(H 4 BTEC) 0.5 ]·(H 2 O)·2Cl (2). 1 has a two-dimensional (2D) layered structure, while 2 has a zero-dimensional (0D) structure. As expected, 1 and 2 display photochromic behavior of electron transfer. Furthermore, the photo-controlled luminescence and potential application as inkless and erasable printing media are also investigated. • Two photochromic compounds based on a rigid thiazolothiazole extended viologen moiety have been got. • The photo-controlled luminescence and potential application as inkless and erasable printing media are investigated. • The presence or absence of Zn(II) plays an essential role in the structure and photochromic property. [ABSTRACT FROM AUTHOR]