Boosting Solid-State Luminescence of Thiazolothiazole Viologen by Incorporating Metal Halide Clusters to Hinder π-Stacking.

A new strategy is developed herein to improve the solid fluorescence of thiazolothiazole viologen by using the ZnCl42- cluster as a scaffold to hinder π-stacking. Importantly, the Cl···H bonds are formed in the solid state to sustain the framework and can be automatically dissociated when dissolved in H2O, thus having no impact on the strong emission in aqueous solution. As such, the first case of organic-inorganic viologen-zinc halide named 4PV·ZnCl4 was designed and synthesized, and a significant increase in photoluminescence quantum yield (ΦF) is realized from 4PV·2Br (ΦF = 0%) to 4PV·ZnCl4 (ΦF = 27.0%) in solid and from 97% to 98% in H2O. 4PV·ZnCl4 also displays pH stimuli-responsive naked-eye chromic behavior and photoluminescence with different coloring states and intensities. The multifunctional performance of 4PV·ZnCl4 provides a prerequisite for carrying different information, expanding their promising application in multilevel information encryption.

Isomerization-induced fluorescence enhancement of two new viologen derivatives: mechanism insight and DFT calculations.

The dark-colored viologen radical cations are unstable in air and easily fade, thus greatly limiting their applications. If a suitable substituent is introduced into the structure, it will have the dual function of chromism and luminescence, which will broaden its application field. Here, Vio1·2Cl and Vio2·2Br were synthesized by introducing aromatic acetophenone and naphthophenone substituents into the viologen structure. The keto group (-CH2CO-) on the substituents is prone to isomerize into the enol structure (-CH[double bond, length as m-dash]COH-) in organic solvents, especially in DMSO, resulting in a larger conjugated system to stabilize the molecular structure and enhance fluorescence. The time-dependent fluorescence spectrum shows obvious keto-to-enol isomerization-induced fluorescence enhancement. The quantum yield also increased significantly (T = 1 day, ΦVio1 = 25.81%, ΦVio2 = 41.44%; T = 7 days, ΦVio1 = 31.48%, and ΦVio2 = 54.40%) in DMSO. The NMR and ESI-MS data at different times further confirmed that the fluorescence enhancement was caused by isomerization, and no other fluorescent impurities were produced in solution. DFT calculations show that the enol form is almost coplanar throughout the molecular structure, which is conducive to stabilizing the structure and enhancing fluorescence. The fluorescence emission peaks of the keto and enol structures of Vio12+ and Vio22+ were at 416-417 nm and 563-582 nm, respectively. The fluorescence relative oscillator strength of Vio12+ and Vio22+ enol structures is significantly higher than that of keto structures (f value changes from 1.53 to 2.63 for Vio12+ and from 1.62 to 2.81 for Vio22+), indicating stronger fluorescence emission of the enol structure. The calculated results are in good agreement with the experimental results. Vio1·2Cl and Vio2·2Br are the first examples of isomerization-induced fluorescence enhancement of viologen derivatives, which shows strong solvatofluorochromism under UV light, making up for the disadvantage that it is easy for a viologen radical to fade in air, and providing a new strategy for designing and synthesizing viologen materials with strong fluorescence.

Synthesis and macrocyclization-induced emission enhancement of benzothiadiazole-based macrocycle.

We presented an effective and universal strategy for the improvement of luminophore's solid-state emission, i.e., macrocyclization-induced emission enhancement (MIEE), by linking luminophores through C(sp3) bridges to give a macrocycle. Benzothiadiazole-based macrocycle (BT-LC) has been synthesized by a one-step condensation of the monomer 4,7-bis(2,4-dimethoxyphenyl)-2,1,3-benzothiadiazole (BT-M) with paraformaldehyde, catalyzed by Lewis acid. In comparison with the monomer, macrocycle BT-LC produces much more intense fluorescence in the solid state (ΦPL = 99%) and exhibits better device performance in the application of OLEDs. Single-crystal analysis and theoretical simulations reveal that the monomer can return to the ground state through a minimum energy crossing point (MECPS1/S0), resulting in the decrease of fluorescence efficiency. For the macrocycle, its inherent structural rigidity prohibits this non-radiative relaxation process and promotes the radiative relaxation, therefore emitting intense fluorescence. More significantly, MIEE strategy has good universality that several macrocycles with different luminophores also display emission improvement.

Highly Selective Chloromethanes Detection Based on Quartz Crystal Microbalance Gas Sensors with Ba-MOFs.

Three new metal-organic frameworks (MOFs), {(CH3NH3)3[Ba2(TTHA)(NO3)(H2O)2]}·2H2O (1), {(CH3NH3)4[Ba3(HTTHA)2(H2O)7]}·3H2O (2), and [Ba7(TTHA)2(NO3)2(H2O)10]·2H2O (3) (H6TTHA = 1,3,5-triazine-2,4,6-triamineh-exaacetic acid) have been synthesized and characterized. The sensing properties of 1-3 were explored with regard to volatile organic compounds (VOCs) by the quartz crystal microbalance (QCM) technique. The results indicated that 1 and 2 have a much higher selectivity and response to chloromethanes (CH2Cl2, CHCl3, and CCl4) compared with H2O, CH3OH, CH3CH2OH, CH3CN, (CH3)2CO, C6H6, C6H5CH3, C6H5CH2CH3, and C6H5Cl at room temperature. Furthermore, 1 and 2 sensing film also exhibits excellent reversibility and stability, and the response and recovery times are almost within 10 s. 3 displays a lower response and poor selectivity to the above VOCs. The significant difference may be caused by their different structural characteristics. The Ba2+ ions are all decacoordinated in 1 and 2, while Ba2+ ions have more open metal sites in 3. So, the high selectivity and response of 1 and 2 may be due to the exchange of coordination water molecules with chloromethanes and possible electrostatic effects between (CH3NH3)+ cations and chloromethanes containing more electronegative Cl atoms. DFT calculation results show that the bond energy of Ba-Cl and Ba-O is not much different, so chloromethanes at high concentrations may exchange coordination water to form weak Ba···Cl interactions and show higher response values. 3 has no obvious VOCs selectivity and higher response due to more open sites of Ba2+ ions and smaller pore size. This work develops a fast and effective method to detect chloromethanes, providing a new opportunity for designing QCM gas sensors coated with different MOF materials.

Bis(2-pyridylmethyl)amine-functionalized alizarin: an efficient and simple colorimetric sensor for fluoride and a fluorescence turn-on sensor for Al3+ in an organic solution.

A complexone analog chemosensor, H2L, bearing chelating bis(2-pyridylmethyl) amine and alizarin groups was synthesized via the Mannich reaction. H2L chromically responds to OH-, F-, CH3COO-, and H2PO4- in DMF, CH3CN, and acetone, but not in CH3OH or H2O. The addition of F- ions to H2L selectively induces a significant and visible color change in acetonitrile and shifts both methylene proton signals upfield. H2L also exhibits visible responses to Mg2+, Sr2+, Ba2+, Tb3+, Cu2+, Co2+, Ni2+, Zn2+, Mn2+, Cd2+, and Fe3+ in solution. AlCl3 can form an Al : L = 2 : 3 complex that not only changes the color of the DMF solution, but also significantly increases its fluorescence intensity. The limit of fluorescence turn-on detection for AlCl3 in DMF is 2.7 × 10-8 M, which is an order higher than those of other anthraquinone sensors reported in the literature. NMR spectroscopy shows that hydroxyl is not deprotonated upon interacting with Al3+, but will be partially deprotonated in the presence of Zn2+. Contrary to the complexone, the H2L-Ce(iii) complex does not react chromically to F-. However, the H2L-NiCl2 complex responds chromically to F-, with higher sensitivity (LOD = 1.3 × 10-6 M F- in acetonitrile) than free H2L. The spectral changes in the presence of F- are similar to that of OH-; however, the spectrum shifts slightly to a longer wavelength and is more sensitive to both H2L and the H2L-NiCl2 complex. Moreover, 4% or less H2O in the solvent essentially has no influence on the F- sensitivity; however, high water content significantly decreases the F- sensitivity. The spectral changes of the Zn2+, Cu2+, Fe3+, Ce3+, and Ni2+ complexes in the presence of different NaOH concentrations were also investigated.

An anionic sod-type terbium-MOF with extra-large cavities for effective anthocyanin extraction and methyl viologen detection.

An anionic sod-type zeolitic metal-organic framework [(CH3)2NH2]9{Tb6(η6-TATAT)4(H2O)12}·3Cl·DMA·7H2O [1, H6TATAT = 5,5',5''-(1,3,5-triazine-2,4,6-triyltriimino)tri-1,3-benzenedicarboxylic acid] has been synthesized by metal-ligand directed assembly of hexacarboxylic acid units and Tb3+ ions. Compound 1 with extra-large cavities can efficiently extract natural product anthocyanins from blackberries and release them rapidly into NaCl aqueous solution. And, the nature of the anionic framework makes it very sensitive to detect cationic methyl viologen (MV2+) with a detection limit as low as 1 × 10-8 M.

A Homochiral {CoΙΙ16 CoΙΙΙ4 } Supertetrahedral T4 Cluster from a Racemic Ligand with Ferromagnetic Behavior and High Photocatalytic Activity.

A homochiral mixed-valence cobalt cluster [CoΙΙ16 CoΙΙΙ4 (µ6 -O)4 (µ3 -OH)12 (S-bme)12 (OAc)6 ]Cl6 ⋅5 CH3 OH⋅18 H2 O (1, Hbme=1H-(benzimidazol-2-yl)ethanol) was synthesized from a racemic ligand and three cobalt salts of CoCl2 ⋅6 H2 O, Co(Ac)2 ⋅4 H2 O and Co(NO3 )2 ⋅6 H2 O in a DMF/MeOH mixed solvent. The enantioselective coordination occurs when a large excess of cobalt ions added in the solution and only the S-configuration of the racemic ligand involved in crystallization. The CD spectra of three crystal samples show identical Cotton signals, indicating the repeatability and the enantiomeric purity of the single crystals. This compound presents a beautiful two-shell Matryoshka-type supertetrahedral T4 cluster constructed by an inner CoΙΙΙ4 O4 cubane and four exterior CoΙΙ4 O4 cubanes bridged by µ6 -O2- and µ3 -OH- ions. This highest nuclear chiral cobalt cluster is the first example of enantiopure cobalt cluster separated from a racemic ligand and is the largest supertetrahedral cobalt cluster up to now. The magnetic studies reveal it behaves as a ferromagnet. Photocatalytic properties of 1 show high catalytic activities for the degradation of the highly toxic triphenyl dye crystal violet (CV) in the presence of H2 O2 under visible light in aqueous solution. The degradation rate almost reach 100 % at 45 min and can maintain 98.54 % after 8 cycles.

Phenolacetyl Viologen as Multifunctional Chromic Material for Fast and Reversible Sensor of Solvents, Base, Temperature, Metal Ions, NH3 Vapor, and Grind in Solution and Solid State.

Electron-withdrawing/coordinating o-phenolacetyl-substituted viologen can act as a visual sensor for solvents, bases, and temperature in organic solvents. Due to chelating phenolacetyl groups, this viologen can coordinate to Fe(III), Cu(II), and ZnCl2 in aqueous and DMF solutions. Interestingly, this viologen can respond to temperature, grind, and NH3 vapor in its solid state. Stimuli response is visible, fast, and fully reversible in air at room temperature. The color change is attributed to the enolic and/or free radical structure. This is the most versatile chromic material that responds to chemical and physical stimuli in both solution and solid state.

High Sensitivity Viologen for a Facile and Versatile Sensor of Base and Solvent Polarity in Solution and Solid State in Air Atmosphere.

Viologen cations are excellent electro- and photochromic materials. They generally have no response or very low sensitivity to bases. In this paper, three compounds, 1,1'-bis(2-oxo-2-phenylethyl)-4,4'-bipyridinium (viologen) with different substituents, including H (1), Cl (2), and OH (3), were synthesized. All three, especially 1 and 2, have very high sensitivity to base in both solution and solid state in air atmosphere. These viologens are responsive not only to bases but also to solvent polarity. NMR shows 1 became enolic and then a radical, whereas 3 is colored only in the radical form. These results are in agreement with EPR spectra. Crystal structures show that the C-C that links two pyridinium and N-C distances in coplanar pyridinium in the colored (radical) form is clearly longer than that of the pale-yellow form, indicating that the color is due to the viologen radical. Viologens containing an electron-withdrawing phenacetyl group are the most sensitive compounds for fast, naked eye detection of base and solvent polarity.

A metal-organic framework constructed using a flexible tripodal ligand and tetranuclear copper cluster for sensing small molecules.

A new porous metal-organic framework (MOF) {[Cu4(OH)2(tci)2(bpy)2]·11H2O} (1) based on a tetranuclear copper cluster with intracluster antiferromagnetic interactions was synthesized. Quartz crystal microbalance (QCM) sensor studies reveal sensitive and selective sensing for small molecules.

Two nanocage anionic metal-organic frameworks with rht topology and {[M(H2O)6]6}(12+) charge aggregation for rapid and selective adsorption of cationic dyes.

Two rht anionic metal-organic frameworks were synthesized. There are six [M(H2O)6](2+) ions held together by a super-strong H-bond and arranged in a regular octahedron in each medium cage. Dye adsorption studies revealed a rapid and selective adsorption of cationic dyes and the adsorbed dyes can be released in saturated NaCl aqueous solution.

Ligand field effect tuned magnetic behaviors of two chain compounds based on Mn(III)3O units: from slow magnetic relaxation to metamagnetism.

Two chain compounds built with anti-anti acetate bridged Mn(III)(3)O units, [Mn(3)O(Clppz)(3)(EtOH)(4)(OAc)](n) (1) and [Mn(3)O(Clppz)(3)(EtOH)(2)(OAc)](n) (2), were synthesized and characterized. The magnetic studies indicate that 1 is a single-chain magnet with two slow magnetization relaxation processes which has for the first time been found in this type of chain complex, while 2 shows a field-induced metamagnetic behavior. The quite different magnetic behaviors resulted from the different number of coordinated ethanol molecules on the Mn(III)(3)O unit, four ethanol molecules for 1, and two ethanol molecules for 2. The best fittings to the experimental magnetic susceptibilities gave J(1) = -2.72 cm(-1), J(2) = -4.34 cm(-1), zJ = 1.24 cm(-1) for 1 and J(1) = -5.91 cm(-1), J(2) = -0.98 cm(-1), zJ = 1.71 for 2 above 30 K. The positive zJ values indicate the presence of weak ferromagnetic interactions between the trinuclear units via acetate bridges in 1 and 2.

Self-assembly of high-nuclearity copper cages: tricorne Cu21 and saddlelike cyclic Cu16.

Reaction of cupric salts with H(2)Rppz (R = H, Me; H(2)ppz = 3-(2-hydroxyphenyl)pyrazole; H(2)Meppz = 3-(2-hydroxy-5-methylphenyl)pyrazole) in the presence of sodium azide and triethylamine as bases gave two high-nuclearity copper cage compounds [HNEt(3)](2)[Cu(21)(CH(3)CN)(2)(H(2)O)(mu(2)-N(3))(6)(mu(3)-N(3))(2)(ppz)(18)](H(2)O)(3)(EtOH)(2) (1) and [Cu(16)(EtOH)(2)(H(2)O)(2)(Meppz)(16)]9.5 H(2)O (2), respectively. X-ray crystallographic studies revealed that molecular skeletons of 1 and 2 are unique tricorne Cu(21) and saddlelike cyclic Cu(16) aggregates, respectively. The magnetic properties studies showed overall antiferromagnetic interactions in 1 and 2. Quantum Monte Carlo simulations by using a 3-J model for 1 and a 2-J model for 2 were performed, which indicated that the magnetic couplings within the triangular copper units in 1 are ferromagnetic and those between other copper ions are antiferromagnetic, whereas in 2 all magnetic couplings between adjacent copper ions are exclusively antiferromagnetic.

Pressure effects and Mössbauer spectroscopic studies on a 3D mixed-valence iron spin-crossover complex with NiAs topology.

A three-dimensional mixed-valence iron complex with NiAs-type topology, [(Fe(III)(3)O)Fe(II)(TA)(6)(H(2)O)(3)].(ClO(4))(2)(NO(3))(EtOH)(H(2)O)(2) (1, HTA = tetrazole-1H-acetic acid), shows spin-crossover behavior that was characterized via variable-temperature crystal structures, Mössbauer spectra and magnetic susceptibilities, the pressure effects on the transition behavior were also studied.

Coexistence of magnetization relaxation and dielectric relaxation in a single-chain magnet.

A novel single-chain magnet, [MnIII3O(Meppz)3(EtOH)4(OAc)] (1), has been successfully synthesized from a secondary building block [MnIII3O(Meppz)3(EtOH)5Cl] (2) with an S = 1 ground state. SCM 1 exhibits both magnetization relaxation and dielectric relaxation properties.

A three-dimensional supramolecular network built with the zigzag chain complex bis(5-carboxy-1H-imidazole-4-carboxylato)copper(II).

In the title complex, poly[copper(II)-di-mu-5-carboxy-1H-imidazole-4-carboxylato], [Cu(C5H3N2O4)2]n or [Cu(H2Imda)2]n, each imidazole moiety is bonded to the Cu atom via O and N atoms to give a square-planar coordination [Cu-O = 2.014 (2) and 2.016 (2) A, and Cu-N = 1.982 (3) and 1.992 (2) A]. The distorted square-pyramidal geometry at the Cu atom results from coordination to an adjacent O atom [Cu-O = 2.305 (2) A], which generates zigzag chains. There is a sixth, weaker, octahedral coordination to the Cu atom from an inversion-related O atom [Cu-O = 3.090 (2) A], which links the chains into sheets in the (100) plane. Imidazole moieties in the sheets are linked in the [100] direction by pairs of N-H...O and C-H...O hydrogen bonds, thus generating a three-dimensional network.