Photochromic Terbium Phosphonates with Photomodulated Luminescence and Metal Ion Sensitive Detection

Rational selection and modification of rare earth metal centers and photoactive organic linkers enables designable multiphotofunctionality to come to fruition in new hybrid coordination polymer materials. By using a viologen‐functionalized diphosphonate linker, two terbium phosphonate compounds ( Tb‐1 and Tb‐2 ) have been constructed, which display reversible photochromic reactions in response to UV light and soft X‐ray irradiation. In addition, the photo‐induced electron‐transfer reaction can modulate the luminescent emission to thus realize photoluminescence switching behavior. Furthermore, both terbium phosphonates can serve as highly sensitive sensors to probe Cu²⁺ in solution through their luminescence. Thus, they represent the first photochromic examples of lanthanide phosphonate‐based materials with photomodulated luminescence and sensitive detection of metal ions.     

含氯化铜的紫精/聚合物薄膜制备及光致变色性能研究

将氯化铜加入到紫精/聚乙烯吡咯烷酮中,制得了一种可快速褪色、光疲劳性能优异的紫精/聚合物光致变色薄膜,测试了该薄膜的变色性能、褪色性能及光疲劳性能.结果表明,氯化铜的加入使薄膜初次紫外光照时的颜色变浅,但加快了薄膜褪色;当氯化铜与紫精摩尔比为1:1、60℃褪色时,薄膜光照后在610 nm处吸光度的半衰期为9 min,而不合氯化铜的薄膜为54 min,氯化铜含量越高,半衰期越短.含有氯化铜的薄膜,随变色/褪色循环次数增加,光照后的显色加深,氯化铜含量越高,颜色增加的程度越大.该功能薄膜可用于信息存储、太阳镜及智能窗等方面.     

Preparation and photochromic properties of pyrazolones/polyvinyl alcohol composite films

Novel photochromic composite films have been successfully fabricated by dispersing pyrazolone derivative:1,3-Diphenyl-4-(3-chlorobenzal)-5-hydroxypyrazole 4-phenylsemicarbazone (1a) into hydrosol of polyvinyl alcohol (PVA). The microstructure, photochromic behaviors and thermal bleaching properties were investigated by Raman spectroscopy, X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and ultraviolet-visible absorption spectroscopy (UV-vis). The results showed that 1a was not only blended but also well dispersed in the PVA polymer films with a suitable content of chromophore. Upon UV light irradiation, the composite films gradually changed from colorless to yellow and recovered fully to the initial state upon thermal bleaching. The time constants of photochromic reactions were almost the same as those of 1a observed in their crystalline state, indicating that the photochromic phenomenon is barely disturbed by the polymer matrix.     

Photochromic Doped Sol-Gel Materials for Fiber-Optic Devices

Photochromic-doped sol-gel materials have been prepared by adding a spiropyran photochromic dye to a solution of ethoxy silane monomers containing non-reacting ethyl radicals. After polymerization, normal photochromism (i.e., colored material upon UV irradiation) is obtained in the resulting matrix. The sol-gel matrix hinders the organic molecule rotations, thus giving two stable states, which can be reversibly switched by UV and green-blue irradiation respectively.If these materials are attached to optical fibers, the properties of the light throughput may be modified. Simple fiber-optic/photochromic devices made of two optical fibers placed in a V-groove removable connector have been prepared. Once cured, these devices behave as optically addressed variable delay generators. The same devices can be used for preparing simple optical switches and routing systems.     

Novel oxazabicycles as a new class of photochromic colorants

A new photochromic colorant with an oxazabicyclic moiety has been synthesized by an efficient method. It turns pale red upon UV irradiation and undergoes reverse reaction while being heated. This work may open an exciting new avenue for future development of the photochromic dyes with novel molecular structures.     

Readily accessible rhodamine B-based photoresponsive material

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基于紫精组分构筑的三种光致变色共晶体

在碱性条件下,将1,2,4,5-均苯四甲酸(H4BTEC)与过渡金属离子配位,并引入中性紫精组分1-羧乙基-4,4′-联吡啶(CEbpy),构筑了3个同构共晶体[M(H₂O)_5(BTEC)_0.5]·(CEbpy)(M=Mn(1)、Zn(2)、Co(3))。在紫外灯照射下,3个化合物都发生明显的光致变色现象,这归因于光诱导的电子转移并产生了紫精自由基。同时,在加热的情况下,化合物3还表现出不可逆的失水致变色行为,而化合物1和2则没有。我们讨论了金属离子对变色行为的影响。     

Synthesis and characterization of coumarin-based spiropyran photochromic colorants

Two coumarin-based spiropyran derivatives were synthesized and characterized in two steps to explore their photochromic properties. Both prepared compounds are sensitive to UV light and change colors upon irradiation. The resulting photogenerated zwitterions revert to the original compounds while being heated. A new family of organic photochromic colorants is introduced.     

Photochromism of a novel 6pi conjugate system having a bis(2,3'-benzothienyl) unit

A novel photochromic molecule having a bis(2,3'-benzothienyl) unit has been synthesized. The derivative underwent a thermally irreversible photochromic reaction upon alternate irradiation with UV and visible light.     

Syntheses, structures and photochromism of two novel copper(II) complexes with 1,2-bis(2′-methyl-5′-(2″-pyridyl)-3′-thienyl)perfluorocyclopentene

Two novel Cu(II) complexes with 1,2-bis(2′-methyl-5′-(2″-pyridyl)-3′-thienyl)perfluorocyclopentene (BM-2-PTP) or its closed-form (closed-BM-2-PTP) were synthesized and characterized by X-ray crystallographic analysis. Both complexes are tetra-coordinated to two N atoms from distinct ligands and two Cl atoms from anions, forming 1-D polymeric structures. [Cu(BM-2-PTP)Cl₂] (1) showed typical spectral changes as analogous Ag(I) complexes with the same ligand upon appropriate light stimulus. However, closed-BM-2-PTP displayed different photocyclization from its open-ring form upon irradiation with UV light, indicating the photogenerated closed form turned into two kinds of closed-ring isomers. Furthermore, [Cu(closed-BM-2-PTP)Cl₂] (2) was revealed to contain two conformers by X-ray crystallographic analysis and displayed similarities in photocyclization to its free ligand. The distinct absorptions of the UV spectrum were attributed to the coexistence of two conformers in complex 2, both of which showed effective photoreactivities in the crystalline phase. The photochromic mechanism of complex 2 is tentatively concluded as two conformers displaying independent photoreactions.     

Synthesis, crystal structure and characterization of photochromic 1,2-bis{2-ethyl-5-[2-(1,3-dioxolane)]-3-thienyl}perfluorocyclopentene

A novel photochromic diarylethene, 1,2-bis{2-ethyl-5-[2-(1,3-dioxolane)]-3-thienyl}perfluorocyclopentene (BEDTP), was synthesized and its structure was determined by single-crystal X-ray diffraction analysis. Its photochromic and fluorescent properties were also investigated. The results showed that this compound exhibited reversible photochromism, changing from colorless to magenta after irradiation with UV light both in solution and in the crystalline phase. In hexane solution, the open-ring isomer of BEDTP exhibited relatively strong fluorescence at 400 nm when excited at 282 nm. The fluorescence intensity decreased along with the photochromism upon irradiation with 254 nm light and its closed-ring isomer showed almost no fluorescence.     

Tunable photochromism of spirooxazines via metal coordination

Through the incorporation of a phenanthroline ligand into the oxazine moiety of photochromic spirooxazines, a series of photochromic spirooxazine-phenanthroline metal complexes have been synthesized, resulting in tunable and significantly increased photoresponsivities. Such systems are of interest for the investigation of multifunctional photochromic materials. These novel metal complexes retain their photochromic activity in the complexed state, leading to ligand binding in both the spirooxazine and the photomerocyanine forms during the photoconversion. A significant stabilization of the photomerocyanine form results from metal complexation, as indicated by the shift in thermal equilibrium values (KT = 0.06) upon metal complexation (KT = 0.6-1.2). Photoconversion occurs with first-order kinetics, suggesting the absence of an intermediate state. A third photostationary state is observed in these systems induced by visible irradiation of the thermal equilibrium state, leading to a three-state system. This new class of compounds provides the opportunity to investigate the synergy between changes in electronic structure associated with photoisomerization, and metal-centered functionality.     

Chelating Metal Ions in a Metal-Organic Framework for Constructing a Biomimetic Catalyst Through Post-modification

Crystal engineering, as a burgeoning technology, has been widely used to construct metalloporphyrins biomimetic catalysts. Herein, a bimetallic metal-organic framework (MOF) was constructed by 4-(4-carboxyphenyl)-1,2,4-triazole ligand, Co²⁺ and Zr⁴⁺ metal ions by solvothermal reaction(named PFC-88). A N,N-chelation site was found between the two adjacent ligands in PFC-88, consequently a porphyrin-like structure was obtained through chelating Fe³⁺ in this site by post-modification, named PFC-88-Fe. The result of a single crystal X-ray technology verified that Fe ions were successfully metalated in the N,N-chelation site of PFC-88, which is assisted by the X-ray absorption near-edge structure(XANES) spectra. An o-phenylenediamine oxidation reaction was applied to assessing the catalytic activity of PFC-88-Fe, in which the absorbance increases of phenazine-2,3-diamine at λ=418 nm were recorded by absorption spectroscopy in kinetic mode, exhibiting the application potential as a biomimetic catalyst.     

Photochromic metal complexes: photoregulation of both the nonlinear optical and luminescent properties

A series of dithienylethene (DTE)-containing 2,2'-bipyridine ligands and their zinc(II) diacetate, zinc(II) dichloro, rhenium(I) tricarbonyl bromo, and ruthenium(II) bis(bipyridine) complexes have been designed and synthesized, and their photochromic, photophysical, and quadratic nonlinear optical properties have been studied. Upon UV irradiation at 350 nm, the ligands and complexes undergo ring closure of the DTE units, with a good to excellent photocyclization yield. In the case of the Re(I) and Ru(II) complexes, the photocyclization of the DTE units can also be triggered using visible light, upon excitation into the metal-to-ligand charge-transfer (MLCT) bands at 400 and 490 nm, respectively. Molecular quadratic nonlinear optical (NLO) responses of the complexes have been determined by using either the electrical field induced second harmonic generation (EFISH) or harmonic light scattering (HLS) technique at 1910 nm. These studies reveal a large increase of the second-order NLO activity after UV irradiation and subsequent formation of the ring-closed isomers. This efficient enhancement clearly reflects the delocalization of the π-electron system and the formation of strong push-pull chromophores in the closed forms. The combination of the photochromic DTE-based bipyridine ligand with luminescent Re(I) and Ru(II) fragments also allows the photoregulation of the emission, leading to an efficient quenching of the ligand-based 77 K luminescence and demonstrating that the photocontrol of two optical properties, linear and nonlinear, could be achieved by using the same photochromic ligand.     

Development of Photochromic Coatings on Polycarbonate

New photochromic materials based on heteropolyoxometallates (HPOM) incorporated into a hybrid organic-inorganic binder were prepared and coated onto polycarbonate (PC) substrates. The hybrid binder was formed through the controlled hydrolysis and condensation of 3-glycidoxypropyl-trimethoxysilane (GPTMS) and bisphenol A (BPA) by the sol–gel technique. The photochromic behavior of the materials was investigated by using ultraviolet-visible (UV-Vis) absorption spectroscopy and color index values. The results indicated that the films were reduced photochemically to yield a blue species under UV irradiation, with the film color changing to deep blue with increasing time, and HPOM and BPA content. The photosensitivity of several films with molybdenum HPOM showed faster coloration and much slower bleaching than the tungsten HPOM. A photochromic mechanism involving electron transfer between the GPTMS matrix with BPA, and PWO is proposed. After UV irradiation, the O–H and bonds decomposed gradually and W^{6 +} was reduced gradually with increasing time. The photochromic coatings on PC substrate showed reversible transmittance change before and after UV irradiation, making then efficient light protectors under UV irradiation.     

Photoswitching CO2 Capture and Release in a Photochromic Diarylethene Metal–Organic Framework

We demonstrate herein a promising pathway towards low‐energy CO₂ capture and release triggered by UV and visible light. A photosensitive diarylethene ligand was used to construct a photochromic diarylethene metal–organic framework (DMOF). A local photochromic reaction originating from the framework movement induced by the photoswitchable diarylethene unit resulted in record CO₂‐desorption capacity of 75 % under static irradiation and 76 % under dynamic irradiation.     

Multifunctional Viologen-Derived Supramolecular Network with Photo/Vapochromic and Proton Conduction Properties

A supramolecular network [H₄bdcbpy(NO₃)₂·H₂O] (H₄bdcbpy = 1,1′-Bis(3,5-dicarboxybenzyl)-4,4′-bipyridinium) (1) was prepared by a zwitterionic viologen carboxylate ligand in hydrothermal synthesis conditions. The as-synthesized (1) has been well characterized by means of single-crystal/powder X-ray diffraction, elemental analysis, thermogravimetric analysis and infrared and UV-vis spectroscopy. This compound possesses a three-dimensional supramolecular structure, formed by the hydrogen bond and π–π interaction between the organic ligands. This compound shows photochromic properties under UV light, as well as vapochromic behavior upon exposure to volatile amines and ammonia, in which the electron transfer from electron-rich parts to the electron-deficient viologen unit gives rise to colored radicals. Moreover, the intensive intermolecular H-bonding networks in 1 endows it with a proton conductivity of 1.06 × 10⁻³ S cm⁻¹ in water at 90 °C.     

Growth of layered basic zinc acetate in methanolic solutions and its pyrolytic transformation into porous zinc oxide films

Photo-induced reduction of gold and platinum metal salt solutions was carried out using viologen graft copolymerized on low-density polyethylene (LDPE) films and viologen-containing poly(vinylidene fluoride) (PVDF-PVBV) microporous membranes. The effects of the UV irradiation time and concentration of the metal salt solutions on the metal ion reduction process and the resultant metal deposition on the polymeric substrates were investigated. The metal-polymer composites were characterized using X-ray photoelectron spectroscopy (XPS), scanning and transmission electron microscopy (SEM and TEM), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and UV-visible absorption spectroscopy. The amount of metal uptake, the state of the metal, and the size of the metal particles were found to be strongly dependent on the UV irradiation time and the type and concentration of the metal salt solution. The microporous structure and the high viologen content of the PVDF-PVBV membrane constitute an effective matrix for metal ion reduction and preparation of metal nanoparticles.     

Determining the magnitude and direction of photoinduced ligand field switching in photochromic metal-organic complexes: molybdenum-tetracarbonyl spirooxazine complexes

The ability to optically switch or tune the intrinsic properties of transition metals (e.g., redox potentials, emission/absorption energies, and spin states) with photochromic metal-ligand complexes is an important strategy for developing "smart" materials. We have described a methodology for using metal-carbonyl complexes as spectroscopic probes of ligand field changes associated with light-induced isomerization of photochromic ligands. Changes in ligand field between the ring-closed spirooxazine (SO) and ring-opened photomerocyanine (PMC) forms of photochromic azahomoadamantyl and indolyl phenanthroline-spirooxazine ligands are demonstrated through FT-IR, (13)C NMR, and computational studies of their molybdenum-tetracarbonyl complexes. The frontier molecular orbitals (MOs) of the SO and PMC forms differ considerably in both electron density distributions and energies. Of the multiple π* MOs in the SO and PMC forms of the ligands, the LUMO+1, a pseudo-b(1)-symmetry phenanthroline-based MO, mixes primarily with the Mo(CO)(4) fragment and provides the major pathway for Mo(d)→phen(π*) backbonding. The LUMO+1 is found to be 0.2-0.3 eV lower in energy in the SO form relative to the PMC form, suggesting that the SO form is a better π-acceptor. Light-induced isomerization of the photochromic ligands was therefore found to lead to changes in the energies of their frontier MOs, which in turn leads to changes in π-acceptor ability and ligand field strength. Ligand field changes associated with photoisomerizable ligands allow tuning of excited-state and ground-state energies that dictate energy/electron transfer, optical/electrical properties, and spin states of a metal center upon photoisomerization, positioning photochromic ligand-metal complexes as promising targets for smart materials.     

Structure, photochromic, and electrochemical properties of dioctadecylamine/H3PMo12(O)40 Langmuir-Blodgett film

We used the Langmuir-Blodgett (LB) technique to construct a well-defined and structure-controllable photochromic material-a highly ordered multilayer film composed of dioctadecylamine and 12-molybdophosphoric acid (PMo12). We identified well-ordered lamellar structures using X-ray diffraction, polarized IR, and Raman spectra, and we determined a packing model of the two components in the LB film. We found the Keggin structure and fundamental features of the PMo12 ion to be maintained in the hybrid film. This hybrid LB film displayed photochromic properties upon UV light irradiation and we observed the following process from first-order kinetics. The photochromism exhibited the ability to switch between colorless and blue. A fading process occurred when the film was exposed to ambient air or O2 in the dark. During the color change, the packing structure of the film was well maintained. We also examined the electrochemical behavior of the hybrid LB film by cyclic voltammetry in detail and we propose different kinetic mechanisms for the film before and after irradiation.