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

Crystal structures of 1,1'-bis-(carb-oxy-meth-yl)-4,4'-bipyridinium derivatives

The crystal structures of 2-[1'-(carb-oxy-meth-yl)-4,4'-bi-pyridine-1,1'-diium-1-yl]acetate tetra-fluoro-borate, C14H13N2O4 +·BF4 - or (Hbcbpy)(BF4), and neutral 1,1'-bis-(carboxyl-atometh-yl)-4,4'-bi-pyridine-1,1'-diium (bcbpy), C14H20N2O8, are reported. The asymmetric unit of the (Hbcbpy)(BF4) consists of a Hbcbpy+ monocation, a BF4 - anion, and one-half of a water mol-ecule. The BF4 - anion is disordered. Two pyridinium rings of the Hbcbpy+ monocation are twisted at a torsion angle of 30.3 (2)° with respect to each other. The Hbcbpy monocation contains a carb-oxy-lic acid group and a deprotonated carboxyl-ate group. Both groups exhibit both a long and a short C-O bond. The cations are linked by inter-molecular hydrogen-bonding inter-actions between the carb-oxy-lic acid and the deprotonated carboxyl-ate group to give one-dimensional zigzag chains. The asymmetric unit of the neutral bcbpy consists of one-half of the bcbpy and two water mol-ecules. In contrast to the Hbcbpy+ monocation, the neutral bcbpy mol-ecule contains two pyridinium rings that are coplanar with each other and a carboxyl-ate group with similar C-O bond lengths. The mol-ecules are connected by inter-molecular hydrogen-bonding inter-actions between water mol-ecules and carboxyl-ate groups, forming a three-dimensional hydrogen-bonding network.

Photo/Electrochromic Dual Responsive Behavior of a Cage-like Zr(IV)-Viologen Metal-Organic Polyhedron (MOP)

Stable stimulus-responsive materials are highly desirable due to their widespread potential applications and growing demand in recent decades. Despite the fact that viologen derivatives have long been known as excellent photochromic and electrochromic materials, the development of stable viologen-based multifunctional smart materials with short coloration times remains an exciting topic. To obtain photochromic and electrochromic dual responsive materials, embedding the viologen ligand into a robust metal oxide cluster to increase its stability and sensitivity is an effective strategy. Herein, a viologen-based metal-organic polyhedron (MOP) {[Zr₆L₃(μ₃-O)₂(μ₂-OH)₆Cp₆]·8Cl·CH₃OH·DMF} [Zr-MOP-1; H₂L·2Cl = 1,1'-bis(4-carboxyphenyl)-4,4'-bipyridinium dichloride, and Cp = η⁵-C₅H₅] was successfully prepared and characterized. It consists of trinuclear Zr-oxygen secondary building units and exhibits reversible photochromic and electrochromic dual responsive behaviors. As expected, the designed robust viologen-based nanocage with a V₂E₃ (V = vertex, and E = edge) topology can maintain its stability and rapid photo/electrochromic behaviors with an obvious reversible change in color from purple (brown) to green, mainly due to the enclosed cluster structure and the abundant free viologen radicals that originate from the effective Cl → N and O → N electron transfers. Spectroelectrochemistry and theoretical calculations of this Zr-MOP were also performed to verify the chromic mechanism.

A Series of Polyoxometalate-Viologen Photochromic Materials for UV Probing, Amine Detecting and Inkless and Erasable Printing

In this work, by using two kinds of viologen ligands three POM-based Compounds were obtained under hydrothermal conditions, namely [Ag^I (bmypd)_0.5 (β-Mo₈ O₂₆ )_0.5 ] (1) (bmypd ⋅ 2Cl=1,1'-[Biphenyl-4,4'-bis(methylene)]bis(4,4'-bipyridyinium)dichloride), [Ag^I ₂ (bypy)₄ (HSiW₁₂ O₄₀ )₂ ] ⋅ 14H₂ O (2) and [Ag^I (bypy)(γ-Mo₈ O₂₆ )_0.5 ] (3) (bypy⋅Cl=1-Benzyl-4,4'-bipyridyinium chloride). The structures were characterized by Fourier transform infrared spectroscopy (FT-IR), Powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS) and single crystal X-ray diffraction. Compounds 1-3 show excellent photochromic ability with fast photoresponse under the irradiation of ultraviolet light with different degrees of color changes. So compounds 1-3 can be used as visible ultraviolet detectors. Compounds 1-3 also possess photoluminescence properties with fast and excellent fluorescence quenching effect. Compounds 1-3 also can be used as inkless and erasable printing materials with suspensions of 1-3 applied to filter paper. Compounds 1-3 can also produce color changes in amine vapor environment, especially in an NH₃ atmosphere. Compounds 1-3 can be used as organic amine detectors.