Viologen Complex Research Articles

Structures and photochromic behavior of viologen-based compounds: Insights from Mn(II) and Cd(II) complexes

This study investigates the crystal structures and photochromic properties of two viologen-based compounds [Mn(CMbpy)(BTEC)0.5(H2O)4]·0.5(H2BTEC)·3H2O (1) and [Cd(CMbpy)(1,2,4-BTC)(H2O)]n (2) [CMbpyBr = 1-(1-cyclohexylmethane)-4,4′-bipyridinium bromide, H4BTEC=1,2,4,5-benzenetetracarboxylic acid, 1,2,4-H3BTC=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.

Interlocking viologen-based lanthanide complexes for multifunctionality: Photochromism, electrochromism, photoluminescence, photomagnetism, and inkless printing and UV shielding applications

The construction of molecular crystal materials with physical properties that can be dynamically controllable through various stimuli such as light and electricity is of extraordinary significance, while this remains a tremendous challenge. In this context, we demonstrate two novel 2-D multi-function viologen complexes, {[Ln(bcbp)(BDC)(CH3OH)(H2O)2]·Cl·CH3OH·H2O}n (1-Eu, and 2-Dy; H2bcbp·2Cl = 1,1′-bis(4-carboxyphenyl)-(4,4′-bipyridinium) dichloride; BDC = p-phthalic acid, and Ln = Eu, Dy). Due to the strong π-π interaction between viologen and BDC in the interlocked structure, both compounds exhibit rapid and reversible responses under the stimuli of UV light and electricity. Furthermore, accompanying the photochromic process, photo-modulated luminescent and photomagnetic behavior have been observed. Considering the excellent photochromic performance, the function filter paper and smart organic glass were successfully prepared and used for ink-free printing and UV light filtering.

Two novel Zn(II)-thiazolothiazole extended viologen complexes with photochromism, inkless and erasable printing and photo-modulated luminescence

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) (H2O)]·DMF·3H2O}n (1) and [Zn(H2O)6]0.5 (p-BDC)0.5·(TTVP)0.5 (2) (m-H3BTC = 1,2,4-benzenetricarboxylic acid, p-H2BDC = 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.

Incorporation of a one-dimensional electron-rich chain in viologen-based coordination polymers for super photochromic properties and improved optical applications in polyvinyl alcohol film

1D electron-rich complex chain was incorporated to the viologen complex (1), resulting in robust photochromic properties, distinct ET pathways, and applications in optics. And 1-PVA film can improve the photochromism of viologen complexes.

Cu/Ni Keggin-based viologen complexes with water-assisted 1D proton channels for asymmetric supercapacitors

Cu/Ni Keggin viologen complexes with one-dimensional proton channels are synthesized and directly used as excellent materials for supercapacitors. The 1//AC ASC exhibits an energy density of 9.39 W h kg−1 at a power density of 6000 W kg−1.

A series of viologen complexes containing thiophene and Br- dual fluorescent chromophores for continuous visual sensing of pH and Hg2.

The mercury ion (Hg2+) is a typical high-toxicity substance that can cause severe damage to the environment and human bodies. For the detection of Hg2+, there are still significant challenges in the detection range and limit of detection (LOD). In this study, three viologen-based fluorescent probes are developed, CdCl4(Btybipy) (1), ZnBr4(Btybipy) (2), CdBr4(Btybipy) (3) (Btybipy = bis-1-thiophen-3-ylmethyl-[4,4']-bipyridinyl) through conventional solvent methods for detecting pH and Hg2+. Reversible discoloration and fluorescence response behaviour in the pH range of 4-12.8 is demonstrated by viologen-based fluorescent probes, which exhibit "ON-OFF-ON" signal changes. Compared with complex 1, it is surprising to find that complexes 2-3 display both fluorescence enhancement and fluorescence quenching simultaneously with the addition of different concentrations of Hg2+ (0-20 and 25-400 μM). There is broad linearity in the range of 0-20 and 50-300 μM with LODs of 2.14 and 3.13 nM, respectively. This occurrence of dual-signal modes is attributed to the participation of Br- and the thiophene S atom as dual chromophores in the coordination reaction of Hg2+. Dual-signal mode output, high sensitivity, wide detection range, and low LODs are exhibited by these fluorescent probes. The unique coordination reaction between Br- and the thiophene S atom with Hg2+ can provide a potential strategy for the exploitation of promising sensing platforms for monitoring Hg2+.

A new photochromic Mg(II)‐viologen complex with photoswitchable emission and its application in ink‐free printing

AbstractStimulus‐responsive molecular photochromic materials have potential applications in sensor, information storage, and optical switch devices since they undergo reversible color changes upon stimulus from external light. In this work, a viologen‐derived Mg(II) coordination complex with molecular formula [Mg(dpbp)2(H2O)4] (1) has been synthesized from 1‐(3,5‐dicarboxyphenyl)‐4,4′‐bipyridinium chloride (H2dpbp⋅Cl) under solvothermal conditions. Complex 1 has a three‐dimensional viologen‐based hydrogen bond network showing reversible photochromism through radical formation under ultraviolet‐visible light irradiation. Simultaneously, the emission of complex 1 can be reversibly modulated by ultraviolet‐visible light irradiation. Importantly, due to its reversible photochromic properties, practical fading time, and high stability, complex 1 can be used as an ink‐free and erasable printing medium by applying ultraviolet visible light irradiation with a mask.

A series of zinc coordination compounds showing persistent luminescence and reversible photochromic properties via charge transfer

Long persistent luminescence materials have wide application prospects in the fields of optical communication, sensors, and anticounterfeiting. Recently, some researchers have proved the feasibility of charge transfer effect in the construction of visible light excited room temperature phosphorescence (RTP) materials. However, materials with electronic effects require elaborate design to exhibit long-lived phosphorescence. Herein, a series of coordination compounds based on viologen ligand HL⋅Cl (4-carboxybenzyl)-4,4′-bipyridinium chloride) and Zn2+ with benzoic acid derivatives (o-, m-, p-phthalic acid) were reported. They exhibit not only reversible photochromic properties, but also long-lived persistent phosphorescence. Three complexes possess different structures through different auxiliary ligands with different optical physical properties. Complex 1 exhibits dynamic phosphorescence emission at low temperatures. Interestingly, we synthesized the first viologen complex (complex 2) with excitation wavelength dependent fluorescence, and the emission color gradually changed from blue to red with the increase of excitation wavelength. In addition, the applications of three complexes in data encryption and anticounterfeiting are further demonstrated. This work not only presents coordination compounds with dynamic afterglow materials, excitation wavelength- and time-dependent emission properties, but also provides a new strategy for the charge transfer effect in visible light-excited RTP materials.

Multistimuli-Responsive Materials Based on Zn(II)-Viologen Coordination Polymers and Their Applications in Inkless Print and Anticounterfeiting.

Recently, stimuli-responsive materials have attracted great attention, while most of them respond to single or two stimuli. Thus, it is essential to design multifunctional stimuli-responsive materials and develop their applications. The strategy that constructing high-dimensional coordination polymers facilitates the application scope of a viologen-based photochromic system is put forward and confirmed for the first time. Herein, a novel multistimuli-responsive viologen-based Zn-MOF with a two-dimensional framework has been successfully designed and synthesized. Complex 1 exhibits chromic behavior under a variety of external stimuli such as 365 nm UV, X-rays, heat, electricity, and ethylamine. More interestingly, the crystal state of complex 1 displays dual fluorescence and room-temperature phosphorescence (RTP) emission and emits a yellow afterglow when turning off the UV lamp. In addition, Eu(III)-functionalized hybrids, Eu3+@Zn-MOF, were prepared by coordinated postsynthetic modification based on viologen complexes for the first time. The sample of Eu3+@Zn-MOF inherits the photochromic characteristics of the viologen complexes and gives the distinctive fluorescence of the europium ions. Based on the multicolor switching of 1 and Eu3+@Zn-MOF, their possible practical utilization was successfully developed in the fields of inkless, erasable print media, electrochromic information tag printing, information encryption, and anticounterfeiting.

Voltage-Gated Membranes Incorporating Cucurbit[n]uril Molecular Containers for Molecular Nanofiltration.

Smart voltage-gated nanofiltration membranes have enormous potential for on-demand and precise separation of similar molecules, which is an essential element of sustainable water purification and resource recovery. However, the existing voltage-gated membranes are hampered by limited selectivity, stability, and scalability due to electroactive monomer dimerization. Here, for the first time, the host-guest recognition properties of cucurbit[7]uril (CB[7]) are used to protect the viologen derivatives and promote their assembly into the membrane by interfacial polymerization. Viologen functions as a voltage switch, whereas CB[7] complexation prevents its dimerization and improves its redox stability. The inhibited diffusion of the CB[7]-viologen complex enables the precise patterning of the surface structure. The resultant voltage-gated membrane displays 80% improved rejection performance, excellent recovery accuracy for similar molecules, and anti-fouling properties. This work not only provides an innovative strategy for the preparation of voltage-gated smart nanofiltration membranes but also opens up new avenues for ion-selective transmission in water treatment, bionic ion channels, and energy conversion.

Photochromism and thermochromism: new strategies for (HV)[Co(H2O)6](p-BDC)2(DMF)·H2O

A new strategy for a viologen complex, (HV)[Co(H2O)6](p-BDC)2(DMF)·H2O (1) (p-BDC = 1,4-benzene dicarboxylate, DMF = N,N-dimethylformamide), was designed by keeping highly symmetrical hydrogen bonding and maximum π⋅⋅⋅π stacking interactions. By the reaction of Co(NO3)2·6H2O with 1,1′-bis(n-hexyl)-4,4′-bipyridinium dibromide (HVBr2) and 1,4-benzenedicarboxylic acid (p-H2BDC), the viologen complex 1 was prepared with monoclinic space group P 2/n, which is constituted by HV2+ cation, [Co(H2O)6]2+ cation, DMF and constitution water as well as two p-BDC2− anions to form a supramolecular 3D framework. The viologen complex 1 exhibits photochromic and thermochromic property. The types and regions of intercontacts in viologen complex 1 were illustrated by Hirshfeld surface and two-dimensional (2D) fingerprint plots in crystal stacking. The frontier molecular orbital was evaluated to explain the matching rules between electron acceptor and donor at the density functional theory (DFT)-B3LYP/6-311 (d, p) level. It is of great signifcance to investigate inter/intramolecular interaction and chromic property of viologen complex 1 and provide theoretical guidance for the self assembly design and decoration of viologen complexes.

The modulation effect of pi–pi interactions on the electronic and photochromic properties of viologen complexes containing N,N′-bis(carboxyethyl)-4,4′-bipyridinium

Two viologen complexes containing N,N′-bis(carboxyethyl)-4,4′-bipyridinium (BCEbpy) were prepared, namely [Zn(H2O)6]·(BCEbpy)·(p-BDC)·3H2O (1) and [Co(H2O)6]·(BCEbpy)·(p-BDC)·3H2O (2) (p-H2BDC = 1,4-benzenedicarboxylic acid), and their crystal structures, photochromism, frontier molecular orbitals, Hirshfeld surfaces and 2D fingerprint plots were investigated. The modulation effects of pi–pi interactions were explored on the electronic and photochromic properties of compounds 1 and 2. Due to the existence of photo-response viologen radicals, both complexes 1 and 2 display excellent photo-response properties in the sequence 1 < 2. The results indicate that compound 1 exhibits intramolecular electron transfer; compound 2 exhibits both intramolecular and intermolecular electron transfer, which is mainly due to the change of electronic and steric structures caused by pi–pi interactions with a faster photo-response rate than that of compound 1. The donor–acceptor modes, matching principles and inter/intramolecular atom–atom close contacts were illustrated by the density functional theory (DFT)-B3LYP/6-311(d,p) method.

Three Mn–viologen complexes containing 1-carboxyethyl-4,4′-bipyridinium: crystal structures, photochromism and theoretical calculations

Three Mn–viologen complexes containing CEbpy were prepared and displayed excellent photochromic properties by intramolecular or intermolecular electron transfer.

DFT/TD-DFT investigation on the photoinduced electron transfer of diruthenium and viologen complexes

Photoinduced electron transfer, chemical stability, and redox property of diruthenium−viologen complexes were investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. Target systems include a series of diruthenium and viologen complexes consisting of Ru(bpy)3-viologen-Ru(bpy)3; Ru–V–Ru, Ru(bpy)3-viologen-Ru(bpy)(dcbpy)2; Ru–V–RuCOOH, and Ru(bpy)3-viologen-viologen-Ru(bpy)3; Ru–V–V–Ru, where bpy = 2,2′-bipyridyl and dcbpy = 4,4′-dicarboxyl-2,2-bipyridyl. The B3LYP functional was used to investigate the ground state properties for the three diruthenium and viologen complexes and for two parent complexes: ruthenium-bipyridine (Ru(bpy)32+) and methyl viologen (MV2+) as well as their oxidized states. Singlet excited states were examined using the TD-DFT calculations with CAM-B3LYP functional in acetonitrile using conductor polarizable continuum model (CPCM). The TD-DFT calculations reproduced the experimentally observed variation of the absorption spectra due to oxidation states. The correlation between the calculated UV–Vis transition and molecular orbitals for the excited state clearly established that the viologen dication (V2+) changed their reductive product into the radical cation (V•+) and neutral (V0), whereas ruthenium retained its formal Ru(bpy)32+ oxidation state. The metal to ligand charge transfer state of Ru(bpy)32+ was shown to undergo electron transfer quenching by methyl viologen dication (MV2+). These findings are relevant for the development of novel optoelectronic materials owing to a combination of chemical stability, redox activity, and long-lived excited states.

Pyrene-viologen complexes in SDS micelles: quenching parameters and use as probes of aggregation numbers.

Through a formal-kinetic treatment, we rigorously derive the micellar occupations in the presence of fluorophore-quencher ground-state complexes and the resulting expressions for the time-dependent and stationary observables in the case of combined static and dynamic quenching. We present a protocol for data analysis that effectively isolates the processes, thereby ensuring rapid fit convergence and unique parameter sets. By this approach, we interpret time-resolved fluorescence measurements on pyrene quenched by a homologous series of viologens in SDS micelles. The dynamic intramicellar quenching is diffusion limited; and the formation of the ground-state complexes is entropy driven, with a constant increment per methylene group in the viologen sidechains. The micellar aggregation numbers are obtained with a precision comparable to neutron scattering, including their temperature dependence.

Hot electron transfer in Zn-Ag-In-Te nanocrystal-methyl viologen complexes enhanced with higher-energy photon excitation.

The dynamics of hot electron transfer from Zn–Ag–In–Te (ZAITe) nanocrystals (NCs) to adsorbed methyl viologen (MV2+) were investigated by transient absorption spectroscopy. The bleaching of the exciton peak in the ZAITe NC–MV2+ complexes evolved faster than that of ZAITe NCs. The hot electron transfer efficiency increased from 45% to 72% with increasing excitation photon energy.

Effect of counter cations on the photochromic behaviors of three Zn–viologen complexes

Similar viologen cations, regular change in acceptor moieties and photochromism provide an ideal model for elucidating D–A matching rules.

A Multi‐Responsive Cd–Viologen Complex: Photochromism, Photomodulated Fluorescence, and Luminescent Sensing

AbstractBy incorporating a viologen moiety into a framework, a multiresponsive 2D bilayered luminescent Cd–viologen complex {[Cd1.5(Cebpy)(Hbtc)Cl]⋅H2O}n, (1, Cebpy=1‐carboxyethyl‐4, 4’‐bipyridine, H3Hbtc=1, 3, 5‐benzenetricarboxylic acid) has been synthesized. The reversible photochromism from light brown to dark bluish‐grey is implemented due to the favourable spatial stack of the electron donor and acceptor. The photochromic component of the organic linkers can modulate the luminescence of compound 1 under irradiation by using a Xenon lamp. At the same time, compound 1 shows a good potential in luminescent sensing for colored transition metal cations. Thus, multiphotofunctionality, viz. photoluminescence, photochromism as well as the derivate fluorescent responses to irradiation and colored transition metal cations have been combined in the Cd–viologen complex 1, which is the first example in the Cd–viologen‐based photochromic hybrid materials.

Photochromic and photomodulated luminescence properties of two metal–viologen complexes constructed by a tetracarboxylate-anchored bipyridinium-based ligand

Photochromic and photomodulated luminescence properties of two metal–viologen complexes constructed using a tetracarboxylate-anchored bipyridinium-based ligand are reported.

Photochromic Properties of a Series of Zinc(II)–Viologen Complexes with Structural Regulation by Anions

The solvothermal reaction of 1-(3,5-dicarboxybenzyl)-4,4′-bipyridinium chloride (H2L+Cl–) with different anionic Zn(II) salts leads to three diverse metal–viologen complexes, formulated as {[Zn(HL)Cl2]2·2H2O} (1), {[Zn3(L)2(H2O)8]·2(SO4)·2(H2O)}n (2), and {[Zn(L)H2O]·NO3·H2O}n (3). Single-crystal X-ray analyses revealed that complex 1 displays dinuclear structure. Complex 2 features a 2D layered structure, which consists of four-fold interpenetrating stacked layers with sulfate ions locating between the sheets. Complex 3 shows a 3D two-fold interpenetrating framework with nitrate anions interspersing the void space of the framework, and it features an uninodal three-connected ThSi2 (ths) topology. The structural disparities reveal that the different geometries of counterions, coordination modes, and conformations of ligand L–, together with the deprotonation degree of aromatic carboxylate, have great influence on the formation of various structures. Interestingly, complexes 1–3 are all photoactive to UV–v...