Search

A zinc-organic hybrid (1) with multifunctional room temperature phosphorescence (RTP) was synthesized. 1presents light/force-sensitive RTP properties due to the photochromic behavior from gray to light yellow and the transition from crystalline to amorphous state, respectively. Furthermore, inkless printing and information encryption models were successfully constructed to prove their widespread application prospect.

A series of Ln(III)-based coordination compounds with one-dimensional chains have been synthesized by assembling organic phosphonate ligands hydroxyethylidene diphosphonate (HEDP) and the imidazole derivative 2,4,5-tris(4-pyridyl)-imidazole (TPI) with the lanthanide ions under solvothermal conditions. Based on the electron-donor/-acceptor property, the isomorphic compounds exhibit radical-actuated photochromic behavior induced by the electron transfer process under light illumination at room temperature. In addition, taking advantage of the abundant hydrogen-bond interactions in the structures, the compounds display significant proton conduction behavior in the temperature range of 303–343 K at 100% relative humidity. Importantly, proton conductivities of all compounds increase by about 100% compared to the initial state after light irradiation. As a result, this work shows new hybrid complexes with photochromic and photomodulated proton conduction characteristics, providing a method for the design of intelligent and multifunctional materials with diverse photochromism and tunable proton conduction.

Photochromic materials, with the changes of their physical and chemical properties under the stimulation of light, have been widely utilized in the fields of optical switches, displays, and molecular devices. Herein, a series of binuclear lanthanide complexes [RE2(9-Ac)6(DMF)2] (DMF = N,N′-dimethylformamide; RE = Dy for 1, Gd for 2, Tb for 3, and Y for 4) were constructed based on the single ligand of 9-anthracene carboxylic acid (9-HAc). Their crystal structures and magnetic properties were characterized. All the compounds showed radical-actuated photoluminescent and photochromic behavior with the color varied from faint yellow to brown, as confirmed by UV–vis, fluorescence, and electron paramagnetic resonance spectra. Distinct from the photochromic materials governed by photoactive ligands or mixed ligands, this work not only provides a general method for building photochromic materials based on a single ligand but also enriches RE-based photochromic or photoresponsive material systems.

The rational design of 2D polyoxometalate-based metal–organic framework (POMOF) nanosheets on a conductive substrate as a self-supporting electrode is highly attractive but a great challenge. Herein is the first demonstration of POMOF nanopillar arrays consisting of 2D nanosheets as a self-supported electrode for the hydrogen evolution reaction (HER) in acidic conditions. Single-crystal X-ray analysis reveal that our as-prepared 2D [Co2(TIB)2(PMo12O40)]·Cl·4H2O [named CoMo-POMOF; TIB = 1,3,5-tris(1-imidazoly)benzene] crystalline materials are connected by Co-α-Keggin polymolybdate units act as secondary building blocks and TIB as the organic ligands. The 2D CoMo-POMOF nanosheets were successfully arrayed on a conductive nickel foam substrate by a facile CoO nanorod template-assisted strategy. Remarkably, the CoMo-POMOF nanopillar arrays demonstrate superior electrocatalytic performance toward the HER with an overpotential of 137 mV and Tafel slope of 59 mV dec–1at 10 mA cm–2, which are comparable to those of state-of-the-art POMOF-based electrocatalysts. Density-functional theory (DFT) calculations demonstrate that the exposed bridging oxygen active sites (Oa) of Co-α-Keggin polymolybdate units in CoMo-POMOF optimize the Gibbs free energy of H* adsorption (ΔGH*= −0.11 eV) and increase the intrinsic HER activity.

The tris(pyridin-4-yl)amine ligand was found to exhibit a radical-actuated coloration phenomenon, and a novel copper-based color-changeable metal–organic framework (MOF) was synthesized via this photoactive ligand. After light irradiation, the photogenerated stable radicals in this framework induced increasing amplitude of magnetization (32%) at room temperature, being the largest enhancement among radical-based photochromic systems.

Hydroxyethylidene diphosphonate (HEDP) and tris(4-pyridyl)amine (TPA) are employed to assist the preparation of a Dy(III)-phosphonate in this work, namely, {[Dy2(H2-HEDP)4]3•2(H3-TPA)•2(H4-HEDP)•xsolvent} (1). The compound features the anionic one-dimensional chain structure templated by the cationic H3-TPA and uncoordinated H4-HEDP molecules. Through the hydrogen bonds between the guest cations and host Dy(III)-phosphonate skeletons, a supramolecular architecture is finally constructed, displaying photochromism and room-temperature phosphorescence (RTP) behaviors. Interestingly, through the protonation of TPA molecules, the radicals generated after photochromism still remain a highly stable character, accomplishing an extremely long-lived state of charge separation. Moreover, the photogenerated radicals can greatly prompt the RTP performance of compound 1, which offers a promising strategy for the construction of tunable optical materials.

Switching on/off single-molecule magnets (SMMs) at room temperature is still a challenge in moleculebased magnets. Herein, two photochromic Ln-based (Ln = Dy, Tb) phosphonate coordinated polymers were synthesized with regulable SMM behavior. The reversible room-temperature photo-coloration was an electron transfer process with a generation of relatively stable radicals, characterized by structural analyses, ultraviolet-visible, luminescence and electron spin resonance spectra and magnetic measurements. Importantly, owing to the antiferromagnetic coupling interactions between Ln3+ions and photogenerated radicals, the room-temperature light irradiation surprisingly switched off the SMM behavior, showing the first example of radicalquenched SMMs in the molecule-based magnets. Moreover, the silient SMM behavior could be recovered after eliminating photogenerated radicals via heat treatment, showing a reversible off/on switch of SMMs vialight and heat. This work constructs a system for switching off/on SMMs through electron transfer photochromism, providing a visual operation way vianaked-eye-detectable coloration for the switchable SMMs.

Exploring the discrete complexes with multi-step coloration is still a challenge in the field of electron transfer photochromic materials. Herein, we synthesized a series of dinuclear Ln-diphosphonate compounds[Ln=Dy(1); Gd(2); Tb(3); Y(4)] with a remarkably and reversibly photoactive coloration phenomenon. These compounds showed two-step coloration behavior, which were the first discrete architectures in the reported electron transfer photochromic complexes. This two-step coloration phenomenon was originated from the large distortion of H3-TPT acceptors, which in turn reduced the π-conjugation of electron acceptors and slowed the decay process of electron transfer. The photogenerated stable doublet radicals originated from electron transfer from diphosphonate donor to polypyridine acceptor in these complexes were detected by UV-Vis and electron spin resonance(ESR) spectra. Furthermore, the photogenerated radicals were estimated by direct current magnetic susceptibilities and variable temperature ESR spectra, suggesting the doublet radicals in the dinuclear structure for all the compounds. This work revealed a series of discrete phosphonate-based systems with a multi-step coloration process, providing a new pathway for designing multicolor photochromic materials with potential photoswitching or other applications.

Crystalline complexes that exhibited light switchable proton conductivity are of great interest but still a challenge in material science. Herein, a terbium phosphonate chain complex was synthesized through assembly of electron-rich phosphonate units, electron-deficient polypyridine components and paramagnetic Tb3+ions. Vialight irradiation and heat treatment, the photogenerated radicals could simultaneously and reversibly tune the photochromic, luminescent and magnetic properties. Originated from the abundant hydrogen bonding networks formed between PO3groups and lattice water molecules, proton conductive behaviour was explored with high proton conductivity of (1.74±0.19)×10−3S cm−1at 80 °C and 100% relative humidity. Importantly, accompanied with the colorless sample changed to blue, the proton conductivity increased about 20% after room temperature light illumination, implying that light irradiation could act as an external stimulus to enhance the conductive properties of original material. This work innovatively realized the light responsive conductive property in the electron transfer photochromic materials, providing a novel strategy for the construction of smart materials.

Stimulating tunable room-temperature phosphorescence (RTP) is still a challenge in photochromic systems, which is vital for multifunctional coordination materials. Herein, we synthesized two new photochromic chain complexes through self-assembly of the nonphotochromic 1,3,5-tris(4-pyridyl)benzene ligand, diphosphonate, and Ln(III) ions (1for Ln(III) = Dy and 2for Ln(III) = Gd). Both compounds showed fast photoresponses with the color turning from yellow to dark gray with a reversible decoloration by heating or storage in the dark. The electron transfer photochromic behavior with the generated stable radicals was further confirmed by the room-temperature UV–vis and electron paramagnetic resonance spectra. Furthermore, via tuning the generation and disappearance of stable radicals, reversible room-temperature fluorescence and phosphorescence for both compounds were switched by light irradiation and a thermal treatment, with an enhanced intensity for RTP and a decrease in fluorescence during the duration of Xe-lamp light irradiation. This work provides a new strategy that photogenerated radicals could promote and enhance RTP properties in functional materials.

Proton conductive materials have attracted extensive interest in recent years due to their fascinating applications in sensors, batteries, and proton exchange membrane fuel cells. Herein, two Fe-diphosphonate chains (H4-BAPEN)0.5·[FeIII(H-HEDP)(HEDP)0.5(H2O)] (1) and (H4-TETA)2·[FeIII2FeII(H-HEDP)2(HEDP)2(OH)2]·2H2O (2) (HEDP = 1-hydroxyethylidenediphosphonate, BAPEN = 1,2-bis(3-aminopropylamino)ethane, and TETA = triethylenetetramine) with different templating agents were prepared by hydrothermal reactions. The valence states of the Fe centers were demonstrated by 57Fe Mössbauer spectra at 100 K, with a high-spin FeIIIstate for 1and mixed high-spin FeIII/FeIIstates for 2. Their magnetic properties were determined, which featured strong antiferromagnetic couplings in the chain. Importantly, the proton conductivity of both compounds at 100% relative humidity was explored at different temperatures, with 2.79 × 10–4S cm–1at 80 °C for 1and 7.55 × 10–4S cm–1at 45 °C for 2, respectively. This work provides an opportunity for improving proton conductive properties by increasing the relative number of protons and the carrier density using protonated flexible aliphatic amines.

Exploitation of room temperature (RT) photochromism and photomagnetism to induce single-molecule magnet (SMM) behavior has potential applications toward optical switches and magnetic memories, and remains a tremendous challenge in the development of new bulk magnets. Herein, a series of chain complexes [Ln3(H–HEDP)3(H2–HEDP)3]·2H3–TPT·H4–HEDP·10H2O (QDU-1; Ln = Dy (QDU-1(Dy)), Gd (QDU-1(Gd)), and Y (QDU-1(Y)); HEDP = hydroxyethylidene diphosphonate; TPT = 2,4,6-tri(4-pyridyl)-1,3,5-triazine) were synthesized by solvothermal reactions. All the compounds exhibited reversible photochromic and photomagnetic behaviors via UV light irradiation at RT, induced by the photogenerated radicals via a photoinduced electron transfer (PET) mechanism. More importantly, the PET process induced significant variations in magnetic interactions for the Dy(III) congener. Strong ferromagnetic coupling with remarkably slow magnetic relaxation without applied dc fields was observed between DyIIIions and photogenerated O•radicals, showing SMM behavior after RT illumination. For the first time, we observed the reversible RT photochromism and photomagnetism in the lanthanide-based materials. This work realized the radicals-actuated on/off SMM behavior via RT light irradiation, providing a new strategy for constructing the light-induced SMMs.

It is still challenging to construct novel photochromic and photomagnetic materials in the field of molecular materials. Herein, the 2,4,6-tris-2-pyridyl-1,3,5-triazine (TPTz) molecule was found to display photochromic properties under room temperature light irradiation. Two mononuclear structures, [Ni(H2O)(TPTz)(C2O4)]·2H2O (1; C2O42–= oxalate) [Ni(H2O)(TPTz)(C2O4)]·0.5H2O (2), and one chain compound [Ni(TPTz)(H2–HEDP)]·2H2O (3; HEDP = hydroxyethylidene diphosphonate) were obtained by assembling TPTz with polydentate O-ligands (oxalate and phosphonate) and the paramagnetic Ni2+ions. The electron-transfer (ET)-dominated photochromism was observable in 1and 2after light irradiation with the photogeneration of relatively stable radicals, and the resultant photochromism was demonstrated via UV–vis, photoluminescence, X-ray photoelectron spectra, electron paramagnetic resonance spectra, and molecular orbital calculations. Due to the denser stacking interactions between the adjacent organic molecules, 2exhibited a faster photochromic rate than 1. Compared with 1and 2, compound 3did not show photochromic behavior, which was deciphered by the theoretical calculations for all of the compounds. Importantly, the magnetic couplings appeared between photogenerated radicals and paramagnetic Ni2+ions, resulting in a scarcely photomagnetic phenomenon of 1and 2in the Ni-based electron transfer photochromic materials. This work enriches the available kind of ligands for the design of ET photochromic materials, putting forward a method to tune the electron transfer photochromic efficiency in the molecular materials.

Two series of lanthanide phosphonates, [H4BAPEN]1.5·[Ln2(HEDP)3]·5H2O [Ln = Gd3+(1-Gd), Tb3+(1-Tb), Dy3+(1-Dy)] and [H4BAPEN]0.5·[LnLi(HHEDP)2(H2O)2]·2H2O [Ln = Gd3+(2-Gd), Tb3+(2-Tb), Dy3+(2-Dy)] (HEDP = 1-hydroxyethylidenediphosphonate) displaying diverse structures have been successfully constructed templated by a protonated aliphatic organic amine 1,2-bis(3-aminopropylamino)ethane (BAPEN). The connection of Ln(III) ions and the diphosphonate ligand generates the one-dimensional (1D) chains for both series 1and 2. Interestingly, 2D layered heterometallic diphosphonate networks were fabricated in series 2wherein the adjacent Ln–HHEDP chains are joined together through the linkage of Li+. Notably, the compounds feature interesting proton conduction behavior. The conductivity increases smoothly with rising temperature, indicating that these compounds could act as promising candidates for temperature sensing. Moreover, the magnetic properties of them have been investigated.

Solvated lanthanide (Ln) cations as templates were employed to assist the fabrication of a series of iodocuprates {[Ln(DMSO)7(CH3OH)][Cu5I7]·I}n[Ln = Eu3+(1), Tb3+(2), Dy3+(3)] (DMSO = dimethyl sulfoxide) and {[Ln(DMF)8][Cu8I11]}n[Ln = Eu3+(4), Tb3+(5), Dy3+(6)] (DMF = N,N-dimethylformamide). The obtained materials are equipped with good photoluminescence and magnetic properties by virtue of the functional Ln3+ions. The synthetic strategy, structural analysis, and properties for these multifunctional materials are discussed in detail. Notably, based on 4and 5, a Ln-doped iodocuprate {[Eu0.37Tb0.31Tm0.32(DMF)8][Cu8I11]}n(7) was successfully constructed, exhibiting white-light emission at room temperature when excited by UV light, which offers a novel strategy to obtain promising optical function materials. Moreover, the combination of Ln3+and iodocuprates in this work provides a new way to construct multifunctional molecular materials.

Electron transfer in solid is crucial to switchable magnetic, electrical, optical and mechanical properties. However, it is a formidable challenge to control electron-transfer behaviors via manipulation of crystalline phases, especially through dynamic crystalline transformation. Herein, three crystalline phases of an {Fe2Co2} compound were obtained via enhancement of intermolecular π···π interactions inducing successive single-crystal-to-single-crystal transformations, from solvated 1·2CH3OH·4H2O, to desolvated 1and its polymorph 1aaccompanying electron transfer. 1·2CH3OH·4H2Oshowed thermally induced reversible intermetallic electron transfer in mother liquor. No electron-transfer behavior was observed in 1. 1ashowed reversible intermetallic electron transfer upon thermal treatment or alternative irradiation with 808- and 532-nm lasers at cryogenic temperatures. The electron-transfer behaviors significantly change the magnetic and optical properties, providing a strategy to realize different electron-transfer behaviors and switchable functions via π···π interactions manipulated dynamic crystalline transformation.

Electron transfer photochromic materials with photo-triggered radicals have received huge interest from chemists due to their potentialities in anticounterfeiting, displays, energy conversion, and information storage. However, utilizing the sole carboxylic acid to synthesize novel electron transfer photochromic species is still confronted with huge challenges. Herein, an acentric three-dimensional network Cd2(ADC)2(DMF)2(H2O) (1; ADC = anthracene-9,10-dicarboxylate; DMF = N,N-dimethylformamide) and a two-dimensional layer Zn(ADC)(H2O)·DMA·H2O (2; DMA = N,N-dimethylacetamide) were synthesized and characterized via a photoactive H2ADC ligand. Both compounds exhibited electron transfer photochromism with the formation of radical photoproducts at the solid state, which was revealed by IR, UV–Vis absorption, photoluminescence and electron spin resonance spectra, and magnetic susceptibility measurements. Density functional theory calculations for 1showed that the coloration process is a metal-assisted ligand-to-ligand electron transfer process between adjacent ADC molecules, and photogenerated stable radicals are delocalized over the ADC components. Compared with 1, the shorter distances between ADC components via coordination bonds promoted 2to exhibit a higher coloration efficiency and larger quantity of photogenerated radicals. Furthermore, both compounds showed unexpected radical-actuated photochromism in aqueous solution. This work showed that the carboxylic acid ligands, without viologen acceptors, could construct the electron transfer photochromic complexes, showing a novel kind of ligand for the design of hybrid photochromic materials.

Photomagnetic materials have attracted enormous attention due to the adjustable coloration and magnetization via light irradiation, while challenges still exist for drastically tuning the magnetism at room temperature. Herein, a novel multifunctional crystal complex (H3-TPB)[Fe(C2O4)3]·H2O (1; C2O42–= oxalate and TPB = 1,3,5-tris(4-pyridyl)benzene) is constructed by self-assembly of paramagnetic Fe3+ions, electron donor oxalate, and electron acceptor TPB ligands. After light irradiation, the compound 1undergoes unidirectional electron transfer (ET) from oxalate to TPB ligands and Fe3+ions, which not only results in the decomposition of oxalate and generation of radicals and Fe2+species but also leads to remarkable ET-triggered photochromism. Importantly, room temperature light irradiation changes the magnetic behavior of 1from weak to strong antiferromagnetism. Moreover, thanks to the stability of the photogenerated radicals, the photoresponsive proton conductivity property for 1is also explored and photoenhanced proton conductivity is observed after photoirradiation.