Visible Light Catalyzed Oxidative Reactions Using Silver-Based Metal-Organic Frameworks Based on Metalloligands

Photocatalysis plays a crucial role in modern organic synthesis by enabling efficient transformations under mild conditions and reducing the need for harmful reagents. Its ability to harness visible light for sustainable chemical processes makes it an attractive alternative to conventional methods. In this study, we have utilized two silver-based MOFs, incorporating two different Co3+-metalloligands, as photocatalysts for oxidation reactions and oxidative coupling processes. The reactions include the oxidation of phenylboronic acids to phenols and the oxidative coupling of amines and anilines to imines and azo compounds. Ag-MOFs demonstrated significant visible light absorption and excellent chemical stability, with superoxide radicals identified as the primary reactive oxygen species. The photocatalytic performance is supported by band gap energy calculation and photophysical studies, including electrochemical impedance, electron paramagnetic resonance, and photoluminescence spectroscopies. The photocatalytic performance of an Ag-MOF was critically influenced by its architecture, including the presence of argentophilic interactions. Such a feature not only enhanced its structural stability but also improved the light absorption, a more significant number of active sites, better charge separation, and a remarkable photocatalytic outcome.

Advances in crystalline metal-organic photochromic materials

Metal-organic materials have undergone rapid advancements due to their unique structural properties and exceptional application potential. As a key branch, crystalline metal-organic photochromic materials (CMOPMs), have attracted significant attention for their ability to modulate physical properties in response to light stimulation, thereby expanding the research landscape of metal-organic materials in areas such as molecular switch, gas adsorption and separation, and sensing applications. Furthermore, light as a renewable and clean energy source significantly enhances its application potential. In this feature article, we review the design and synthesis strategies, classification, and applications of CMOPMs. Finally, we present the opportunities and challenges for the development of CMOPMs.

Template Synthesis of Iodocuprate and Iodoargentate with Photocatalytic Activity and Second Harmonic Generation Efficiency

In virtue of the cationic tri(pyridin-4-yl)amine (TPA) derivatives acting as the templates, two iodometallates, [Me3HTPA]2[CuI3][Cu10I16] (1) and [Me3TPA][Ag5I8] (2), were constructed with different architectures. Compound 1 features a discrete [Cu10I16]6- cluster, which is further combined with [CuI3]2- and two [Me3HTPA]4+ moieties through electrostatic interactions to result in a 3D supramolecular framework. Two types of infinite Ag-I chains with different orientations are formed in iodoargentate 2, and adjacent chains, together with in situ N-methylated cations, are further aggregated into a final 3D supramolecule. The syntheses, crystal structures, and optical properties have been studied. Notably, compound 1 displays efficient visible-light-driven photocatalytic performance for the degradation of dye pollutants. The catalytic mechanism was investigated through radical trapping experiments as well as theoretical calculations. Moreover, both the iodocuprate and iodoargentate hybrids exhibit second harmonic generation (SHG) effects, which are comparable to and even better than that of KH2PO4, indicating that the iodometallate hybrids templated by TPA-based cations could potentially serve as new candidates for second-order nonlinear optics (NLO) materials.

A novel viologen-based hybrid crystalline material for photochromic glass films, information storage and anti-counterfeiting

Information storage and anti-counterfeiting are two very important applications of photochromic materials. Photochromic materials with both information storage and anti-counterfeiting should meet the requirements including fast coloration, good stability and reversibility, low storage cost, and practical application value. Herein, a novel viologen-based coordination polymer, Cd[(pbpy)0.5(HBTC)Cl]·2H2O (1) (pbpy = 1,1'-[1,4-phenylenebis-(methylene)]bis(4,4'-bipyridinium); HBTC2- = 1,3,5-benzenetricarboxylic acid), has been constructed. Compound 1 not only exhibits selective amine sensing properties, but also shows excellent photochromic properties, and the anti-counterfeiting of a two-dimensional code can be also realized through the color-changing behavior. Meanwhile, photochromic glass films of compound 1 were prepared, and compared to traditional optical information storage technology, these photochromic glass films have better water resistance and stability, improving their practical application stability. This work has further enriched the application of photochromic materials in the field of sensing, anti-counterfeiting and information storage.

The effect of conjugation degree of aromatic carboxylic acids on electronic and photo-responsive behaviors of naphthalenediimide-based coordination polymers

Three novel naphthalenediimide-based (NDI-based) coordination polymers (CPs), namely [Cd(3-PMNDI)(2,2'-BPDC)] (1), [Cd2(3-PMNDI)1.5(4,4'-BPDC)2(H2O)3]·DMF (2) and [Cd(3-PMNDI)(4,4'-SDC)] (3) (2,2'-H2BPDC = 2,2'-biphenyldicarboxylic acid, 4,4'-H2BPDC = 4,4'-biphenyldicarboxylic acid, 4,4'-H2SDC = 4,4'-stilbenedicarboxylic acid, 3-PMNDI = N,N'-bis(3-pyridylmethyl)-1,4,5,8-naphthalenediimide, and DMF = N,N'-dimethylformamide), have been designed and synthesized here from electron-deficient PMNDI (electron acceptors, EAs) and electron-rich aromatic carboxylic acids (electron donors, EDs) in the presence of cadmium ions. The introduction of aromatic carboxylic acids with different sizes and conjugation degrees leads to the generation of a two-dimensional (2D) layer in 1, a two-fold interpenetrated three-dimensional (3D) network in 2 and an eight-fold interpenetrated 3D framework in 3. Furthermore, the use of distinct electron-donating aromatic carboxylic acids and the consequent different numbers and strengths of lone pair-π and π-π interactions in the interfacial contacts of EDs/EAs give rise to distinct intermolecular charge transfer (ICT) and initial colors of the three CPs, and consequently cause different photoinduced intermolecular electron transfer (PIET) and distinguishing photo-responsive behaviors (weak photochromic performance for 1, excellent photochromic properties for 2 and non-photochromism for 3). This study indicates that an appropriate ICT is beneficial for PIET, but too weak or too strong ICT is not conducive to PIET, which provides an effective strategy for the construction of functional CPs with distinguishing photo-responsive properties through the subtle balance of ICT and PIET.

Molecular modification effects on the electrochromic and photochromic properties of diarylethene with intramolecular isomerization behavior

Diarylethene (DAE) is one of the most widely used functional units for electrochromic or photochromic materials. To better understand the molecular modification effects on the electrochromic and photochromic properties of DAE, two modification strategies, substitution with functional groups or heteroatoms, were investigated theoretically by density functional theory calculations. It is found that red-shifted absorption spectra caused by a decreased highest occupied molecular orbital-lowest unoccupied molecular orbital energy gap and S₀ → S₁ transition energy during the ring-closing reaction become more significant by adding different functional substituents. In addition, for two isomers, the energy gap and S₀ → S₁ transition energy decreased by heteroatom substitution of S atoms with O or NH, while they increased by replacing two S atoms with CH₂. For intramolecular isomerization, one-electron excitation is the most effective way to trigger the closed-ring (O → C) reaction, while the open-ring (C → O) reaction occurs most readily in the presence of one-electron reduction. Moreover, it is confirmed that substitution with strong electron donating groups (-OCH₃/-NH₂) or with one O/two CH₂ heteroatoms leads to a more favorable closed-ring (O → C) reaction. Functionalized with strong electron-withdrawing groups (-NO₂ and -COOH) or one/two NH heteroatom substitutions, the open-ring (C → O) reaction is easier. Our results confirmed that the photochromic and electrochromic properties of DAE can be tuned effectively by molecular modifications, which provides theoretical guidance for the design of new DAE-based photochromic/electrochromic materials.

The modulation effect of auxiliary ligands on photochromic properties of 3D naphthalene diimide coordination polymers

Two novel naphthalene diimide (NDI) coordination polymers (CPs), [Cd(NicNDI)(4,4'-SBC)] (1) and [Cd(NicNDI)(2,2'-BPC)] (2) (NicNDI = (3-pyridylacylamino)-1,4,5,8-naphthalene diimide, 4,4'-SBC = 4,4'-stilbene dicarboxylic acid, 2,2'-BPC = 2,2'-biphenyl dicarboxylic acid), were designed and prepared by the combination of electron-deficient NicNDI and electron-rich aromatic carboxylic acid ligands in the presence of cadmium ions. The usage of aromatic carboxylic acid ligands with different conjugation degrees, sizes, shapes and charge densities leads to the generation of distinct interpenetrated three-dimensional (3D) frameworks. Interestingly, photochromism of 1 and weak photoactivity of 2 should be attributed to the introduction of different auxiliary ligands and consequently the formation of distinct interfacial contacts of electron donors (EDs)/electron acceptors (EAs) (d_π-π = 3.427 Å, infinite -ED-EA-ED-EA- for 1vs. d_π-π = 3.634 Å, discrete ED-EA-ED for 2), suggesting a subtle modulating effect of auxiliary ligands on interfacial contacts, photoinduced intermolecular electron transfer (PIET) and photoresponsive behaviors.

Solvent-Modulated Self-Assembly of Naphthalenediimide-Based Cd(II) Complexes and the Controllable Photochromism via Conformational Isomerization

Rational regulation of the properties of photochromic materials is a challenging and meaningful work. In the present work, NDI-based complexes, namely, [Cd_0.5(NDI)(HBDC)]·H₂O (1) and a series of conformational isomers of {[Cd(NDI)_0.5(BDC)]·MeCN}_n (2), were synthesized by varying the solvent conditions (H₂BDC = terephthalic acid, NDI = N,N'-bis(3-pyridylcarbonylhydrazine)-1,4,5,8-naphthalene diimide). Complex 1 exhibits a 0D mononuclear structure without photochromic behavior due to the bad conjugation of the naphthalene diimide moiety. The conformational isomers of complex 2 manifest a 3D network, showing ultra-fast photo-induced intermolecular electron transfer photochromic behavior under X-ray, UV, and visible light. However, they show different photochromic rates and coloring contrast upon photoirradiation, which originates from their difference in the distances of lone pair(COO)···π(NDI). This was realized via controlling the solvent ratio in the reaction system. In addition, compared to UV/X-ray light, 2 exhibits greater sensitivity to visible light and is an organic-inorganic hybrid material with photomodulated luminescence. Based on the excellent performance, complex 2 can be applied to filter paper, showing potential applications as an inkless printing medium and selective perception of ammonia and amine vapors in the solid state via different visual color changes.

Photoactive perylenediimide metal–organic framework for boosting iodoperfluoroalkylation of alkenes and oxidative coupling of amines

A novel photoactive MOF was prepared based on an electron-deficient perylenediimide derivative, which exhibits excellent photocatalytic activities towards the iodoperfluoroalkylation of alkenes and the oxidation of amines to imines.

Lattice solvent controlled photochromism of tripyridyl-triazine-based zinc bromide complexes

Two tripyridyl-triazine-based zinc complexes exhibit lattice solvent controlled and solvent-induced photochromic properties.

Inserting protonated phenanthroline derivatives to interchain voids of anionic halometallate units to generate hybrid materials with tunable photochromic performance

Hybrid photochromic materials (HPMs) have potential application in many fields like display, protection, information storage. The generation of HPMs with tunable photochromic performance is meaningful for the availability of smart...

Ultrafast visible-light photochromic properties of naphthalenediimide-based coordination polymers for visual detecting/filtering blue light

Two novel naphthalenediimide-based (NDI-based) coordination polymers (CPs) [Cd∙(3-PMNDI)∙(HNDC)2∙(DMF)] (1) and [Cd∙(4-PMNDI)∙(NDC)]∙DMF (2) (H2NDC = 1,4-naphthalenedicarboxylic acid, 3-/4-PMNDI = N,N′-bis(3-/4-pyridylmethyl)-1,4,5,8-naphthalenediimide, DMF = N,N′-dimethylformamide), have been designed and synthesized, which are constructed...

Modulating the structure and photochromic performance of hybrid metal chlorides with nonphotochromic 1,10-phenanthroline and its derivative

Hybrid photochromic materias (HPMs), especially crystalline HPMs (CHPMs), have been widely investigated due to their feasibility in maintaining the advantages of each constituent and genearating captivating photomodulated functionality. Metal-organic complexes (MOCs), as promising candidates for fabricating CHPMs, have attracted the interest of researchers. The molecular predesign of ligands plays a crucial role in yielding MOC-based CHPMs with tunable photochromic functionality. Hitherto, a great majority of CHPMs are driven by photosensitive ligands. However, the complicated synthesis and high cost of photosensitive ligands obviously prevent the macro-synthesis and future application of these CHPMs. Thus, it is indispensable to explore novel branches of CHPMs. Herein, we report a series of photochromic solid materials bearing modulated photochromic properties by hybridizing metal chlorides with a nonphotosensitive coplanar dipyridine unit 1,10-phenanthroline (phen) and its derivative 5-chloro-1,10-phenanthroline (5-Cl-phen). The resulting hybrids, [ZnCl₂(phen)] (1), [CdCl₂(phen)] (2), [PbCl₂(phen)] (3), [ZnCl(H₂O)(5-Cl-phen)₂]Cl·2H₂O (4), [Cd₂Cl₄(5-Cl-phen)₂] (5) and [Pb₂Cl₄(5-Cl-phen)₂] (6), exhibit distinct structures from the isolated molecular complexes (1 and 4) to the hybrid chain (2, 3, 5 and 6) because of the distinct coordination mode of central metal ions and chloride ions. After photo-irradiation with a Xe-lamp, all complexes, as expected, exhibited apparent color change because of the photoinduced electron transfer (ET) between coordinated chloride ions (Cl^-) as electron donors (EDs) and the coordinated coplanar phen and 5-Cl-phen species as electron acceptors (EAs). More importantly, the photochromic performance of the title complexes could be modulated by phen and 5-Cl-phen. This study provides a general and facile way for modulating the structure and photochromic performance of hybrid metal chlorides with phen or phen-based derivatives under the synergy of crystalline engineering strategy and ET mechanism.

The modulation effect of carboxylic acid ligands on the electron transfer photochromism of NDI-derived coordination polymers

Four naphthalene diimide (NDI)-derived coordination polymers (CPs), [Cd(3-DPNDI)(o-BDC)] (1), [Cd(3-DPNDI)₂(p-BDC)(NO₃)] (2), [Cd(3-DPNDI)(NDC)(H₂O)₂] (3), [Cd(3-DPNDI)(BPC)(H₂O)] (4) (3-DPNDI = N,N'-di-(3-pyridyl)-1,4,5,8-naphthalene diimide, o-BDC = phthalic acid, p-BDC = terephthalic acid, NDC = 2,6-naphthalenedicarboxylic acid, BPC = biphenyl-4,4'-dicarboxylic acid), have been designed and prepared. The usage of carboxylic acid ligands with different sizes, shapes and charge densities leads to the distinct resultant architectures of four CPs and divergent weak interactions (lone pair⋯π, π⋯π and C-H⋯π interactions) of electron donors/acceptors, which further lead to the completely different photoinduced electron transfer (PET) and consequent photochromic properties. More specifically, 1 and 2 display excellent photochromic behaviors with a fast photoresponsive rate and high coloration contrast, which are attributed to the suitable interfacial contacts of electron donors/acceptors. However, 3 and 4 are basically optical inert, which could be attributed to the negative effect of the stronger charge transfer (CT) on PET. The present study illustrates the delicate modulating effect of carboxylic acid ligands on the resultant networks, interfacial relationship and PET together with photoresponsive behaviors.

A multi-responsive indium-viologen hybrid with ultrafast-response photochromism and electrochromism

A novel 0D organic-inorganic metal halide hybrid (C₁₃H₁₆N₂O₂)₂InCl₆·Cl (1) has been obtained by integrating the mono-viologen derivative with InCl₃. Compound 1 exhibits reversible and ultrafast UV/sunlight/X-ray induced photochromic properties, as well as excellent electrochromic performance, which is the first example of an indium-based organic-inorganic chromic hybrid.

An electron-deficient naphthalene diimide-based metal-organic framework for detecting electron-rich molecules through photo-/chemo-induced chromism

A novel naphthalene diimide-based metal-organic framework (MOF) {[Zn(3-DPMNI)_0.5(NDC)]·3DMF} (1@DMF), (H₂NDC = 2,6-naphthalenedicarboxylic acid, DPMNI = N,N'-bis(3-pyridylmethyl)-1,4,5,8-naphthalene diimide, DMF = N,N'-dimethylformamide), has been synthesized, which shows a 3D pillar-layer architecture built of carboxylate layers and naphthalene diimide pillars. The compound exhibits outstanding photochromic performance due to photoinduced electron transfer (ET) between the electron-rich guest molecules and electron-deficient host framework (host-guest ET). Of note, the host framework of 1 cannot show a macroscopic color change owing to the absence of the ET pathway. Nevertheless, it exhibits discriminative photochromic behavior in the presence of electron-rich solvents, which is mainly attributed to different electron-donating abilities of guest solvents and distinct interfacial contacts of electron donors/acceptors. Furthermore, the MOF can also show discriminative ET chemochromic response to different sizes and shapes of organic amines, which can be potentially used for the visual detection of electron-rich organic amines, especially n-butylamine (n-BUA).

Decorating Metal Nitrate with a Coplanar Bipyridine Moiety: A Simple and General Method for Fabricating Photochromic Complexes

As a significant class of photochromic materials, crystalline hybrid photochromic materials (CHPMs) have attracted widespread attention of researchers because of their possibilities for generating other photoresponsive properties and advantages in understanding the underlying relationship between structure and photoresponsive performance. The predesign of suitable ligands plays a major role in generating desirable CHPMs. Hitherto, most CHPMs have been built from photodeformable or photoresponsive tectons. However, the synthesis of these ligands is usually time-consuming and expensive, and this greatly restricts their large-scale preparation and practical application. Therefore, it is necessary to explore new families of CHPMs besides the existing CHPMs. Herein, a simple and general method for constructing CHPMs by decorating metal nitrate with a coplanar bipyridine moiety, namely 1,10-phenanthroline (phen), is reported. The resulting products exhibit photocoloration in response to Xe-lamp irradiation. The electron transfer (ET) from the coplanar NO₃ ^- species (as π-electron donors, π-EDs) to coplanar phen moieties (as π-electron acceptors, π-EAs) is responsible for the resulting photochromism. The influence of the coordination environment and central metal ion on the photochromism was also studied. This work demonstrates that the introduction of coplanar organic tectons as π-EAs to metal nitrates as π-EDs with the collaboration of ET and coordination-assembly strategies is a simple and general method to manufacture CHPMs.

The modulation effect of electron-rich solvents on the supramolecular networks and photochromic properties of naphthalene diimide molecules

The electron-rich solvents can effectively regulate the interfacial contacts of electron donors/acceptors and the photochromic properties of naphthalene diimide molecules.

Template syntheses of diverse haloargentates with reversible photochromism behaviors and efficient photocatalytic properties

A series of haloargentates have been prepared exhibiting a reversible photochromic phenomenon and efficient photocatalytic properties.