Photochromic Hybrid Containing <i>In Situ</i>-Generated Benzyl Viologen and Novel Trinuclear [Bi₃Cl₁₄]^5–: Improved Photoresponsive Behavior by the π···π Interactions and Size Effect of Inorganic Oligomer

Two new member of (V)_{(2<i>n</i>+2)/2}[Bi_2<i>n</i>Cl_8<i>n</i>+2] series hybrids, (BzV)₂[Bi₂Cl₁₀] (<b>1</b>) and (BzV)₅[Bi₃Cl₁₄]₂·(C₆H₅CH₂)₂O (<b>2</b>) (where BzV²⁺ = <i>N</i>,<i>N</i>′-dibenzyl-4,4′-bipyridinium and (C₆H₅CH₂)₂O = dibenzyl ether) have been obtained, and compound <b>2</b> contains an unprecedented discrete trimer [Bi₃Cl₁₄]^5– counterion. The novel <i>in situ</i>-synthesized symmetric viologen cation with aromatic groups on both sides of 4,4′-bipy would provide more opportunities to create π···π interactions to optimize the photochromic property of the hybrid, and different bismuthated-halide oligomers enable us to discuss the size effect in this series of compounds. Both <b>1</b> and <b>2</b> are photochromic, and their photoresponsive rate is faster than that of reported viologen–metal halide hybrids. Experimental and theoretical data illustrated that the size of the inorganic oligomer can significantly influence the photoresponsive rate of the viologen dication, and the π···π interaction behaves as not only a powerful factor to stabilize the viologen monocation radical but also the second electron-transfer pathway, from a π-conjugated substituent to a viologen cation, for the photochromic process

Improved Photochromic Properties on Viologen-Based Inorganic–Organic Hybrids by Using π‑Conjugated Substituents as Electron Donors and Stabilizers

A series of inorganic–organic hybrid compounds L₂(Bi₂Cl₁₀) (L = HMV²⁺ = <i>N</i>-proton-<i>N</i>′-methyl-4,4′-bipyridinium for <b>1</b>, L = HBzV²⁺ = <i>N</i>-proton-<i>N</i>′-benzyl-4,4′-bipyridinium for <b>2</b>, and L = HPeV²⁺ = <i>N</i>-proton-<i>N</i>′-phenethyl-4,4′-bipyridinium for <b>3</b>) have been successfully synthesized by an in situ solvothermal reaction. Compounds <b>1</b>–<b>3</b>, with the same metal halide as anions but different asymmetric viologen molecules as cations, are ideal model compounds for investigating the detailed effect of different photochromically active molecules on the photochromic properties of the hybrids. Compound <b>1</b> shows no photochromic behavior, but compounds <b>2</b> and <b>3</b> possess photochromism and show a faster photoresponse rate than other reported viologen metal halide hybrids. Studies on the relationship between the structure and photochromic behavior clearly reveal that π-conjugated substituents could be used to improve the photoresponsibility and enrich the developed color efficiently and that the π···π interaction among organic components may not only be a powerful factor to stabilize the viologen monocation radical but also act as the second path of electron transfer from the π-conjugated substituent to the viologen cation for the photochromic process, which significantly influences the photochromic properties

Optimized Separation of Acetylene from Carbon Dioxide and Ethylene in a Microporous Material

Selective separation of acetylene (C₂H₂) from carbon dioxide (CO₂) or ethylene (C₂H₄) needs specific porous materials whose pores can realize sieving effects while pore surfaces can differentiate their recognitions for these molecules of similar molecular sizes and physical properties. We report a microporous material [Zn­(dps)₂(SiF₆)] (<b>UTSA-300</b>, dps = 4,4′-dipyridylsulfide) with two-dimensional channels of about 3.3 Å, well-matched for the molecular sizes of C₂H₂. After activation, the network was transformed to its closed-pore phase, <b>UTSA-300a</b>, with dispersed 0D cavities, accompanied by conformation change of the pyridyl ligand and rotation of SiF₆^2– pillars. Strong C–H···F and π–π stacking interactions are found in closed-pore <b>UTSA-300a</b>, resulting in shrinkage of the structure. Interestingly, <b>UTSA-300a</b> takes up quite a large amounts of acetylene (76.4 cm³ g^–1), while showing complete C₂H₄ and CO₂ exclusion from C₂H₂ under ambient conditions. Neutron powder diffraction and molecular modeling studies clearly reveal that a C₂H₂ molecule primarily binds to two hexafluorosilicate F atoms in a head-on orientation, breaking the original intranetwork hydrogen bond and subsequently expanding to open-pore structure. Crystal structures, gas sorption isotherms, molecular modeling, experimental breakthrough experiment, and selectivity calculation comprehensively demonstrated this unique metal–organic framework material for highly selective C₂H₂/CO₂ and C₂H₂/C₂H₄ separation

Optimized Separation of Acetylene from Carbon Dioxide and Ethylene in a Microporous Material

Selective separation of acetylene (C₂H₂) from carbon dioxide (CO₂) or ethylene (C₂H₄) needs specific porous materials whose pores can realize sieving effects while pore surfaces can differentiate their recognitions for these molecules of similar molecular sizes and physical properties. We report a microporous material [Zn­(dps)₂(SiF₆)] (<b>UTSA-300</b>, dps = 4,4′-dipyridylsulfide) with two-dimensional channels of about 3.3 Å, well-matched for the molecular sizes of C₂H₂. After activation, the network was transformed to its closed-pore phase, <b>UTSA-300a</b>, with dispersed 0D cavities, accompanied by conformation change of the pyridyl ligand and rotation of SiF₆^2– pillars. Strong C–H···F and π–π stacking interactions are found in closed-pore <b>UTSA-300a</b>, resulting in shrinkage of the structure. Interestingly, <b>UTSA-300a</b> takes up quite a large amounts of acetylene (76.4 cm³ g^–1), while showing complete C₂H₄ and CO₂ exclusion from C₂H₂ under ambient conditions. Neutron powder diffraction and molecular modeling studies clearly reveal that a C₂H₂ molecule primarily binds to two hexafluorosilicate F atoms in a head-on orientation, breaking the original intranetwork hydrogen bond and subsequently expanding to open-pore structure. Crystal structures, gas sorption isotherms, molecular modeling, experimental breakthrough experiment, and selectivity calculation comprehensively demonstrated this unique metal–organic framework material for highly selective C₂H₂/CO₂ and C₂H₂/C₂H₄ separation

Boosting Antibacterial Photodynamic Therapy in a Nanosized Zr MOF by the Combination of Ag NP Encapsulation and Porphyrin Doping

Antibacterial photodynamic therapy (aPDT) is regarded as one of the most promising antibacterial therapies due to its nonresistance, noninvasion, and rapid sterilization. However, the development of antibacterial materials with high aPDT efficacy is still a long-standing challenge. Herein, we develop an effective antibacterial photodynamic composite UiO-66-(SH)2@TCPP@AgNPs by Ag encapsulation and 4,4′,4″,4‴-(porphine-5,10,15,20-tetrayl)tetrakis(benzoic acid) (TCPP) dopant. Through a mix-and-match strategy in the self-assembly process, 2,5-dimercaptoterephthalic acid containing –SH groups and TCPP were uniformly decorated into the UiO-66-type framework to form UiO-66-(SH)2@TCPP. After Ag(I) impregnation and in situ UV light reduction, Ag NPs were formed and encapsulated into UiO-66-(SH)2@TCPP to get UiO-66-(SH)2@TCPP@AgNPs. In the resulting composite, both Ag NPs and TCPP can effectively enhance the visible light absorption, largely boosting the generation efficiency of reactive oxygen species. Notably, the nanoscale size enables it to effectively contact and be endocytosed into bacteria. Consequently, UiO-66-(SH)2@TCPP@AgNPs show a very high aPDT efficacy against Gram-negative and Gram-positive bacteria as well as drug-resistant bacteria (MRSA). Furthermore, the Ag NPs were firmly anchored at the framework by the high density of –SH moieties, avoiding the cytotoxicity caused by the leakage of Ag NPs. By in vitro experiments, UiO-66-(SH)2@TCPP@AgNPs show a very high antibacterial activity and good biocompatibility as well as the potentiality to promote cell proliferation

Photochromic Metal Complexes of <i>N</i>-Methyl-4,4′-Bipyridinium: Mechanism and Influence of Halogen Atoms

Photochromism of <i>N</i>-methyl-4,4′-bipyridinium (MQ⁺) salts and their metal complexes has never been reported. A series of MQ⁺ coordinated halozinc complexes [(MQ)­ZnX₃] (X = Cl (<b>1</b>), Br (<b>2</b>), I (<b>3</b>)) and [(MQ)­ZnCl_1.53I_1.47]₂(MQ)­ZnCl_1.68I_1.32 (<b>4</b>), with better physicochemical stability than halide salts of the MQ⁺ cation, have been found to exhibit different photochromic behaviors. Compounds <b>1</b>–<b>3</b> are isostructural, but only <b>1</b> and <b>2</b> show photochromism. Introduction of partial Cl atoms to nonphotochromic compound <b>3</b> yields compound <b>4</b>, which also displays photochromism. The photochromic response of <b>1</b>, <b>2</b>, and <b>4</b> indicates the presence of their long-lived charge separation states, which originate from X → MQ⁺ electron transfer according to ESR and XPS measurements. Studies on the influence of different coordinated halogen atoms demonstrate that the Cl atom may be a more suitable electron donor than Br and I atoms to design redox photochromic metal complexes

Photochromic Metal Complexes of <i>N</i>-Methyl-4,4′-Bipyridinium: Mechanism and Influence of Halogen Atoms

Photochromism of <i>N</i>-methyl-4,4′-bipyridinium (MQ⁺) salts and their metal complexes has never been reported. A series of MQ⁺ coordinated halozinc complexes [(MQ)­ZnX₃] (X = Cl (<b>1</b>), Br (<b>2</b>), I (<b>3</b>)) and [(MQ)­ZnCl_1.53I_1.47]₂(MQ)­ZnCl_1.68I_1.32 (<b>4</b>), with better physicochemical stability than halide salts of the MQ⁺ cation, have been found to exhibit different photochromic behaviors. Compounds <b>1</b>–<b>3</b> are isostructural, but only <b>1</b> and <b>2</b> show photochromism. Introduction of partial Cl atoms to nonphotochromic compound <b>3</b> yields compound <b>4</b>, which also displays photochromism. The photochromic response of <b>1</b>, <b>2</b>, and <b>4</b> indicates the presence of their long-lived charge separation states, which originate from X → MQ⁺ electron transfer according to ESR and XPS measurements. Studies on the influence of different coordinated halogen atoms demonstrate that the Cl atom may be a more suitable electron donor than Br and I atoms to design redox photochromic metal complexes

Influence of Supramolecular Interactions on Electron-Transfer Photochromism of the Crystalline Adducts of 4,4′-Bipyridine and Carboxylic Acids

We have studied the electron-transfer photochromism of the crystalline adducts of 4,4′-bipyridine (Bpy) and carboxylic acids and revealed the key structural parameters that decide whether the photochromism can happen for the first time. Experimental and theoretical analyses on nine known examples showed that the hydrogen bonds, instead of π–π stacking interactions, are the defining factor to the photochromism. Only the presence of N–H···O hydrogen bonds can fulfill the electron transfer from the carboxylate group to the Bpy part, although both the N···O separations of O–H···N and N–H···O hydrogen bonds are suitable for the so-called through-space electron transfer. These results can not only help to screen out the photochromic species from the known hundreds of Bpy–carboxylic acid adducts deposited in the Cambridge Crystallographic Data Centre (CCDC) database but also guide the design and syntheses of new adducts using diverse <i>N</i>-heterocyclic aromatic molecules and carboxylic acids

Design and Syntheses of Electron-Transfer Photochromic Metal–Organic Complexes Using Nonphotochromic Ligands: A Model Compound and the Roles of Its Ligands

The model compound [Zn­(HCOO)₂(4,4′-bipy)] (<b>1</b>; 4,4′-bipy = 4,4′-bipyridine) is selected in this work to demonstrate the effectiveness of our previously proposed design strategy for electron-transfer photochromic metal–organic complexes. The electron-transfer photochromic behavior of <b>1</b> has been discovered for the first time. Experimental and theoretical data illustrate that the photochromism of <b>1</b> can be attributed to the electron transfer from formato to 4,4′-bipy and the formation of a radical photoproduct. The electron transfer prefers to occur between formato and 4,4′-bipy, which are combined directly by the Zn­(II) atoms. A high-contrast (up to 8.3 times) photoluminescence switch occurs during the photochromic process. The similarity of photochromic behaviors among <b>1</b> and its analogues as well as viologen compounds has also been found. Photochromic studies of this model compound indicate that new electron-transfer photochromic metal–organic complexes can be largely designed and synthesized by the rational assembly of nonphotochromic electron-donating and electron-accepting ligands