Solid-state UV-vis Diffuse Reflectance Research Articles

Photochromism, Thermochromism, and Electrochromism in Solid-State Host-Guest Inclusion Complexes of β-Cyclodextrin with Dialkylcarboxyl-Substituted Viologens.

Multi-stimuli-responsive chromic materials have immense potential for utilization. Herein, two supramolecular inclusion complexes were prepared by self-assembly of β-cyclodextrin (β-CD) with dialkylcarboxyl-substituted viologens, N,N'-di(3-carboxy-propyl)-4,4'-bipyridinium dichloride (CPV·Cl2) and N,N'-di(6-carboxy-hexyl)-4,4'-bipyridinium dibromide (CHV·Br2). The self-assembled inclusion complexes CPV2+@β-CD and CHV2+@β-CD2 in the solid-state exhibited naked-eye photochromism, thermochromism, and electrochromism in response to multiple external stimuli including light, temperature, and electric field, respectively. Solid-state UV-vis diffuse reflectance and electron spin resonance (ESR) spectroscopy revealed that the observed photochromism, thermochromism and electrochromism are attributed to the formation of viologen free radicals induced by electron transfer under external stimuli. The excellent stimuli-response chromic properties of the title inclusion complexes support their practical utility in visual display, multiple anticounterfeiting, and multilevel information encryption.

Hydrothermal preparation, crystal structure, Hirshfeld surface analysis, photophysical properties and antifungal activity of a series of complexes assembled by 5-bromo-2-(carboxymethoxy)benzoic acid ligands

Five complexes [Co(BCBA)(H2O)3]n (1), [Co(BCBA)(4,4′-Bipy)2·(H2O)]n (2), [Cu(BCBA)(H2O)]n (3), [Zn(BCBA)(H2O)]n (4) and [Cd(BCBA)(2,2′-Bipy)(H2O)·(H2O)]n (5) (H2BCBA= 5‑bromo-2-(carboxymethoxy)benzoic acid, 4,4′-Bipy = 4,4′-bipyridine and 2,2′-Bipy = 2,2′-bipyridine) have been synthesized with H2BCBA ligand by solvothermal condition. All the complexes have been structurally characterized by infrared spectra (IR), elemental analyses and single-crystal X-ray diffraction analyses. Complex 1 is a zero-dimensional structure, and complexes 2–5 are one-dimensional chain structure. Furthermore, thermogravimetric analyses (TGA), Hirshfeld surface analysis, photo-luminescence properties, Solid-state UV–Vis diffuse reflectance spectroscopy and antifungal activity for complexes 1–5 were investigated. The reciprocal H···O/H/Br/C contacts dominate over 86 % of total Hirshfeld surface. Complexes 1–5 have certain inhibitory effects on 8 pathogenic fungi. Among them, complex 5 has the strongest antibacterial activity against Rhizoctonia solani AG1, Sphaeropsis sapinea and Colletotrichum fructicola, and the inhibitory rate reached 100 %.

A new zero-dimensional (0D) hybrid bismuth (III) halide: Synthesis, crystal structure, thermal analysis, photophysical properties and DFT calculations

Low-dimensional organic-inorganic hybrid Bi(III) halides, with organic N, O-heterocycles, are promising solid-state photoluminescent materials, but are underexplored. In this work, we present the synthesis and characterization of a novel bismuth (III) hybrid salt, namely (C8H12NO)4[Bi2Cl10] (referred as (1)). (1) was synthesized using a solvent-evaporation method and extensively characterized using various techniques. The crystal structure of (1) was determined to be zero-dimensional (0D). In this structure, the individual bioctahedral [Bi2Cl10]4− dimers, which share edges, are completely isolated from each other. These dimers are separated by large 4-methoxybenzylammonium cations (C8H12NO)+. The latter are crucial for the crystal structural stability by balancing [Bi2Cl10]4-dimer charges and maintaining overall integrity. Solid-state diffuse reflectance UV–Vis spectrum demonstrates that (1) is a semiconductor with a band gap of 3.32 eV. Its photoluminescence spectrum exhibits intense blue emission when exposed to UV light, with CIE chromaticity coordinates of (0.22, 0.21). Theoretical calculations suggest that the emission with multiple centers originates both from a charge transition between (C8H12NO)+ and Bi2Cl104− ions and from excited-state proton transfer (ESPT) processes related to fluorescence properties. These ESPT processes occur through C–H…π and C–H…O intermolecular hydrogen bonding between the organic cations.

A naphthalenediimide-based Cd-MOF as solvatochromic sensor to detect organic amines

A novel naphthalenediimide-based metal-organic framework, {[Cd(DPNDI)(2,6-NDC)]·2DMF}n (1), has been constructed from mixed ligands of N,N′-Di(4-pyridyl)-1,4,5,8-naphthalene -tetracarboxydiimide (DPNDI) and naphthalene-2,6-dicarboxylic acid (2,6-NDC). 1 displays a two-fold interpenetrated 3D framework related to the 6-c connected pcu topology, which exhibits solvatochromic behavior in the presence of organic amines (electron rich). This solvatochromic behavior was investigated by solid state UV–Vis diffuse reflectance spectra and photo-luminescent spectra, which was arise from the inter-molecular electron-transfer transition from the different solvents to the DPNDI ligand depending on the electron-donating ability of the guest solvents. This work shows that the naphthalenediimide-based MOFs could be used as solvatochromic sensor to detect organic amines.

Synthesis, structure and magnetic properties of a new spin-dimer compound CaCu(SeO3)2

A new selenite compound CaCu(SeO3)2 was obtained by a hydrothermal method. This compound crystallizes in the monoclinic system of space group P21/c, featuring a typical spin-dimer structure. The results of magnetic and heat capacity measurements confirm that this compound has a nonmagnetic singlet ground state, while a fit of magnetic susceptibility using the spin-dimer model suggests a large spin gap of ∼329 ​K in the system. Although CaCu(SeO3)2 and HgCu(SeO3)2 have a similar spin-dimer structure built by [Cu2O8] dimers and SeO3 groups, the spin gap of CaCu(SeO3)2 is much larger than that of HgCu(SeO3)2. Such different spin-gap behaviors may be due to a change on the bonding geometry of spin dimers with a substitution of Ca2+ ions for Hg2+ ions, leading to stronger intradimer and weaker interdimer interaction exchanges in CaCu(SeO3)2. Also, the solid-state UV–vis diffuse reflectance spectrum shows an optical band gap of 2.71 ​eV in the system.

Synthesis, Structure, and Light Absorption Behaviors of Prismatic Titanium-Oxo Clusters Containing Lacunary Lindqvist-like Species.

Exploring new structural types of polyoxotitanium clusters (PTCs), especially those containing classical polyoxometalates structures, has always been the focus of research in the field of metal-oxo clusters. In this work, we present the synthesis and characterization of three prismatic PTCs: namely, Ti8(μ2-O)3(μ4-O)2(OnPr)6(HOnPr)2(L1)8 (PTC-237; H2L1 = 3,5-di-tert-butylcatechol), Ti12(μ2-O)6(μ3-O)8(OnPr)6(L2)12(L3)2 (PTC-238; HL2 = 1-adamantanecarboxylic acid, HL3 = 2-picolinic acid), and [Ti18(μ2-O)4(μ3-O)16(μ5-O)2(OiPr)18(L3)8](L3)2 (PTC-239). Single-crystal X-ray diffraction analyses indicate that the construction of these prismatic PTCs is based on a stepwise interlayer assembly of {Ti3} and {Ti4} substructures. The diameters of their core skeletons are in the range between 0.9 and 1.3 nm. In particular, lacunary Linqvist-like {Ti4} and {Ti5} building units are found to exist in the structures of PTC-237 and PTC-239. According to the solid-state UV-vis diffuse reflectance measurements, the absorption band of 3,5-di-tert-butylcatecholate-functionalized PTC-237 shifts toward the visible-light region, giving a smaller optical band gap of 1.56 eV in comparison to PTC-238 (3.36 eV) and PTC-239 (3.25 eV).

Synthesis, structure and magnetic behaviors of a new fluorophosphate PbCuPO4F

A new fluorophosphate PbCuPO4F was obtained by a hydrothermal method, which is found to crystallize in the monoclinic system with a P21/c space group, exhibiting a tunnel structure built by distorted CuO4F square-pyramids and PO4 tetrahedra. Magnetic measurements show that this compound possesses a short-range magnetic order at ∼7.9 ​K without any antiferromagnetic transitions down to 2 ​K, indicating a singlet ground state. The fit using a modified spin-dimer model indicates intradimer interaction J/kB ​= ​12.2 ​K and interdimer interaction J’/kB ​= ​3.5 ​K in the system, while the critical field for the spin gap between the singlet ground state (S ​= ​0) and the excited triplet state (S ​= ​1) is observed at Hc ​= ​∼4.7 ​T. Although PbCuPO4F and BaCuPO4F have a similar tunnel structure, their magnetic behaviors are remarkably different. This may be due to a slight change of interaction exchange in PbCuPO4F, leading to a coupled spin-dimer of Cu–O–P–O–Cu pathway in the 4-column tunnels. Also, solid-state UV–vis diffuse reflectance spectra show that PbCuPO4F has a wide optical band gap of 3.42 ​eV.

Porous Pyrene Organic Cage with Unusual Absorption Bathochromic-Shift Enables Visible Light Photocatalysis

Porous Pyrene Organic Cage with Unusual Absorption Bathochromic-Shift Enables Visible Light Photocatalysis

Radical-Doped Crystalline Lanthanide-Based Photochromic Complexes: Self-Assembly Driven by Multiple Interactions and Photoswitchable Luminescence.

Stimuli-responsive functional materials, especially the light stimulation color change and tunable fluorescent materials, have received considerable attention because of their broad applications in smart materials. Herein, a series of lanthanide-based [Ln = Nd(III) (1), Sm(III) (2), Eu(III) (3), Gd(III) (4), Tb(III) (5), Yb(III) (6), and Lu(III) (7)] crystalline complexes were attained by simply adding the aqueous lanthanide nitrate solution to the water-soluble naphthalenediimide derivative. The obtained lanthanide-based crystalline materials not only show significant photochromism but also possess reactive organic radicals under ambient conditions. Intriguingly, photoswitchable near-infrared (NIR) fluorescence was realized in the crystalline complex 1. The structures of these crystalline materials were systematically studied to clarify the weak interaction-assisted charge-transfer process. The underlying multiple-interaction-assisted supramolecular self-assembly, the radical-doped nature, and the corresponding photochromic mechanism were thoroughly unearthed by single-crystal X-ray diffraction, in situ solid-state UV-vis diffuse reflectance, and electron paramagnetic resonance spectrometric analysis.

TiO2/g-C3N4 photocatalyst for the purification of potassium butyl xanthate in mineral processing wastewater

In the present work, TiO2-graphite-phase-carbon-nitride (TiO2/g-C3N4) was prepared through a hydrothermal method to obtain a new photocatalytic material. This material was characterized by means of scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray energy spectrometer (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), Solid-state UV–Vis diffuse reflectance spectrometry (UV–Vis-DRS) and electron paramagnetic resonance (EPR). The synthesized TiO2/g-C3N4 exhibited homogeneous morphology, in which TiO2 nanoparticles were uniformly distributed on the g-C3N4 nanosheets. Regarding its potential use as photocatalytic material in the treatment of mineral processing wastewater, 18% TiO2/g-C3N4 showed superior photodegradation performance than TiO2 and g-C3N4, to give 97.1% degradation rate under 100 min of simulated light irradiation. The experimental results showed that the successful incorporation of TiO2 on g-C3N4 nanosheets enhanced the spectral response range of TiO2/g-C3N4, and the photocatalytic activity was improved. In view of that, it can be considered that this kind of photocatalytic material has a good prospect in the treatment of mineral processing wastewater, which would have clearly environmental relevance.

Characterization and luminescence sensing behaviour of a newly constructed hydrolytic stable Pb(II) coordination polymer

Sensing and detecting toxic pollutants like Fe3+, chromate anions and trinitrophenol (TNP) in water are especially important due to their hazardous effects on environmental and ecological systems. In this work, the hydrolytic stable Pb(II) CP {[Pb(asba)(obix)]•2H2O}n (1) [H2asba = 2-amino-4-sulfobenzoic acid, obix = 1, 2-(methylenebenzene)bisimidazole] was constructed and well characterized. 1 exhibits reversible de-/re-hydration behavior. The wide indirect band gap was obtained through the analysis of the solid-state diffuse reflectance UV–Vis spectrum of 1, which is consistent with the calculated value using the CASTEP program in Materials Studio. 1 keeps its crystallinity and structural integrity in various solvents. Interestingly, 1 shows solvent-dependent fluorescence emissions. A strong blue fluorescence emission occurs in water. 1 can sense the Fe3+ and chromate anions selectively and sensitively in the presence of the co-existent different metal cations and inorganic anions, respectively. Moreover, 1 also shows efficient sensing of Fe3+ in the simulative biological system. Furthermore, 1 demonstrates sensitive sensing of TNP. 1 displays excellent recyclability in sensing of these analytes. 1 can determine the related trace analytes in ppm level.

Using thiol-amine solvent mixture to prepare main group heterometallic chalcogenides

By using a n-butylamine (BA)-1,2-ethanedithiol (EDT) solvent mixture as reaction medium, three new heterometallic chalcogenides have been prepared, namely [HBA]2.6[In2.6Sn1.4Se6S2] (1), [HBA]0.8[HR-MP]2[In2.8Sn1.2Se6S2] (2) (R-MP = (R)-2-methylpiperazines) and [H3TAEA]2[InGe4S11(SH)2(OH)] (3) (TAEA = tris(2-aminoethyl)amine). Compounds 1 and 2 feature anionic two-dimensional [InxSn4-xSe6S2]x− layers built up by [M4Q10] (M = In/Sn, Q = Se/S) T2 clusters. Protonated HBA+ and HR-MP+ cations serve as charge balance agents located between the layers. Compound 3 contains discrete [InGe4S11(SH)2(OH)]6− anionic clusters, in which the In3+ ion adopts a unique penta-coordination geometry with five S2− ions. These compounds were characterized by single crystal X-ray diffraction, powder X-ray diffraction, energy dispersive X-ray spectroscopy, solid-state UV–Vis diffuse reflectance spectroscopy, and thermogravimetric analyses. The steep UV–Vis absorption edges indicate the band gaps of 1.86 eV for 1, 2.13 eV for 2 and 2.78 eV for 3.

A novel terbium–mercury compound: Preparation, structure, and properties

Using a hydrothermal reaction, a novel 4f–5d isonicotinic acid complex {[Tb2(IA)6(H2O)4](Hg3Cl7)} n( nHgCl4)· nCl·4 nH3O (1, HIA = isonicotinic acid) was synthesized and it was characterized by single crystal X-ray diffraction technique. Compound 1 is characterized by a two-dimensional layer-like structure. The photoluminescence measurement using solid-state samples uncovered that it shows four emission peaks at 489, 546, 587, and 622 nm, of which the peak at 546 nm is the strongest. These peaks could be assigned to the 5 D4 → 7 F6, 5 D4 → 7 F5, 5 D4 → 7 F4, and 5 D4 → 7 F3 transitions of the Tb3+ ions, respectively. The energy transfer mechanism of the photoluminescence emission was described by means of the energy level scheme of the Tb3+ ions and the isonicotinic acid ligand. Compound 1 shows remarkable CIE (Commission Internationale de I’Éclairage) chromaticity coordinates of (0.3633, 0.5038) in the yellowish green region. Compound 1 possesses a wide semiconductor band gap of 2.97 eV, as unveiled by the solid-state UV-Vis diffuse reflectance experiment.

Synthesis, band structure and multi-responsive luminescence sensing behavior of two Cd(II) coordination polymers

Rapid and sensitive sensing of toxic aromatic compounds has become one of the most important issues. Herein, we use the multifunctional 5-amino-2,4,6-tribromoisophthalic acid (H2ATBIP) to assemble with the Cd(II) ion in the presence of the N-donor bis(imidazole) ligand 1,2-bis(imidazol-1-yl-methyl)benzene (obix) and 1,4-bis(imidazole-l-yl)butane (bib) to construct coordination polymers with pleasing supramolecular architectures and potential interesting luminescent sensing properties. As a result, two Cd(II) coordination polymers, namely, {[Cd(ATBIP)(obix)2(H2O)]·3H2O}n (1) and [Cd(ATBIP)(bib)]n (2), were obtained successfully using the typical solution evaporation method. Single-crystal X-ray diffraction analyses reveal that (1) shows tubular chain structure, while (2) is a necklace-like chain. The central Cd(II) ions in (1) and (2) show slightly distorted octahedral geometry. The ATBIP2- ligand shows monodentate coordination mode in (1) and bischelating coordination mode in (2). With the aid of the hydrogen bonding and the C-Br⋯π interaction, (1) and (2) further extend into a 3D supramolecular network. The analysis of the solid-state diffuse reflectance UV–Vis spectrum reveals that the wide indirect band gaps Eg exist in (1) and (2), which are confirmed by the theoretical calculation based on the density functional theory (DFT). Interestingly, the fluorescence properties of (1) and (2) are greatly dependent on the solvents. Both compounds show multi-responsive sensitive “turn-on” sensing for toluene and “turn-off” sensing for some nitro aromatics (NACs). The sensing limits for toluene and NACs reach to ppm level.

Optical properties of two bismuth(III) halide hybrids with pyridyl sulfide derivative counter cations

Low dimensional organic-inorganic hybrid Bi(III) halides, especially those containing organic N, S-heterocycles are amazing as solid state photoluminescent materials, but remain less explored. Herein, two bismuth(III) halide compounds, (Etmp)4Bi2X10 (X = Cl for 1, Br for 2, Etmp = 4-(ethylthio)pyridin-1-ium), are obtained by employing pyridyl sulfide derivative as counter cations. They are determined as zero-dimensional (0D) ionic structures, featuring binuclear bismuth halide anions charge-compensated by (Etmp)+ counter cations. Solid-state UV–Vis diffuse reflectance spectra reveal the wide optical band gaps of 3.20 eV for 1 and 2.67 eV for 2. Notably, 1 exhibits a strong green photoluminescence emission with a quantum yield of 20%, and a CIE chromaticity coordinate of (0.27, 0.36) when irradiated by a 394-nm light. Theoretical calculations suggest that the charge transition between Cl-3p and p-π* anti-bonding orbital of (Etmp)+ is responsible for the emission.

Heterogeneous palladium SALOPHEN onto porous polymeric microspheres as catalysts for heck reaction

Abstract Catalysts based on porous polymeric microspheres were prepared from N,N′-Bis(3,3′-allyl-salicylidene)-o-phenylenediamine Pd(II) (PdAS) metallo-monomer, styrene (STY), and divinylbenzene (DVB) as co-monomers. The effects of the STY/PdAS mass ratio of co-monomers were investigated to synthesize the optimal catalyst. All the prepared materials were characterized by scanning electron microscopy (SEM), N2 adsorption-desorption isotherms, inductively coupled plasma optical emission spectroscopy (ICP-OES), thermogravimetric analysis (TGA), solid-state diffuse-reflectance UV Vis (DRS UV-Vis) spectrometry, and X-ray photoelectron spectroscopy (XPS). Increasing the PdAS content from 1 to 5 wt%, based on the mass feed of monomers, produced well-defined spherical polymer resins with particle diameters of ~200 μm and high surface areas (>500 m2/g). XPS spectra shown a unique Pd2+ signal associated with the PdAS complex immobilized on a porous resin matrix. The catalytic performances of porous polymer microspheres were evaluated for Heck reaction between iodobenzene and methyl acrylate to produce methyl cinnamate, giving up to 100 % selectivity for the trans-isomer. The resin with 5 wt% PdAS showed the best catalytic activity in methyl cinnamate synthesis. Finally, the best catalytic system was evaluated in octinoxate production producing the target product with the same levels of conversion and selectivity for trans-isomer as was detected for methyl cinnamate synthesis.

A Cobalt-Modified Covalent Triazine-Based Framework as an Efficient Cocatalyst for Visible-Light-Driven Photocatalytic CO2 Reduction.

Photocatalytic CO2 reduction into carbonaceous feedstock chemicals is a promising renewable energy technology to convert solar energy and greenhouse gases into chemical fuels. Here, a covalent triazine-based framework (CTF) is demonstrated as an efficient cocatalyst to reduce CO2 under visible-light irradiation. The nitrogen-rich triazine moieties in CTF contribute to CO2 adsorption, while the periodical pore structure of CTF favors the accommodation of CO2 and electron mediator. Immobilization of cobalt species onto CTF promotes the photocatalytic activity with a 44-fold enhancement over pristine CTF and the optimal CO production rate of the obtained Co/CTFs was up to 50 μmol g-1 h-1 . The results of solid-state UV-vis diffuse reflectance spectra (UV-vis DRS), CO2 adsorption and electrochemical impedance spectroscopy (EIS) illustrated that the increased activity was ascribed to the enhanced CO2 capture capacity, improved absorption of visible-light and facilitated the transfer of charge from CTF to CO2 molecules. The CTF not only serves as a substrate for active Co species, but also bridges the photosensitizer with cobalt catalytic sites for the efficient transfer of photoexcited electrons. This work highlights the capability and ease of fabricating covalent organic framework-based photocatalytic systems that are potentially useful for energy-conversion applications.

A novel holmium–mercury complex: Structure, green photoluminescence, energy transfer mechanism and semiconducting properties

The complex (Ho(IA)3(H3O)(H2O)) n(0.5 nHg2I6) (HIA = isonicotinic acid) has been synthesized via a hydrothermal reaction and has a one-dimensional (1D) chain-like structure. It has an emission band in the green region of 542 nm, which could originate from the 5 S2 → 5 I8 transition of the Ho3+ ion. The compound possesses Commission Internationale de I’Éclairage chromaticity coordinates of (0.2065, 0.4969) and has a wide optical band gap of 2.32 eV, as found by solid-state UV-Vis diffuse reflectance measurements.

C6N2H18][SbI5]: A Lead-free Hybrid Halide Semiconductor with Exceptional Dielectric Relaxation.

[C6N2H18][SbI5] (1), a novel metal halide semiconductor with dielectric relaxation behavior, has been successfully synthesized, in which the cavities between the one-dimensional [SbI5] n2- polyanions are occupied by 2-methyl-1,5-pentanediammonium (2-MPDA) cations. 1 undergoes a reversible solid-state phase transition at TC = 192.7 K and shows a step-like dielectric anomaly. Interestingly, above TC, distinct dielectric dispersion in a wide temperature range is also witnessed. Remarkably, the solid state UV-vis diffuse reflectance spectrum of 1 exhibits a slightly gentler absorption edge at about 650 nm; that is, 1 adopts an indirect band gap with 1.92 electron volts. The combined narrow band gap, strong photoconductivity effect, and excellent dielectric relaxation might shed light on the exploitation of lead-free hybrid metal halide molecular materials with promising application prospects in thermoresponsive relaxation-type dielectric materials and photovoltaic conversion devices.

Synthesis, characterization and luminescent sensing property of a novel Zn(II)-organic coordination polymer

A novel luminescent Zn(II)-organic coordination polymer {[Zn(asba)(mbix)2(H2O)]·H2O·DMF}n (1) based on the multi-functional 2-amino-5-sulfobenzoic acid (H2asba) and the N-donor flexible bis(imidazole) ligand 1,3-bis(imidazole-1-ylmethyl)benzene (mbix) has been synthesized and structurally characterized. 1 shows excellent hydrolytic stability in water. 1 may be used as a potential candidate for wide band gap semiconductor materials through the analysis of the solid state diffuse reflectance UV–vis spectrum. The fluorescence properties of 1 are greatly dependent on the solvents. 1 exhibits the strongest fluorescence in water. Most interestingly, the fluorescence emission of the aqueous suspension of 1 is selectively quenched by the chromate anions (CrO42−/Cr2O72−) or Fe3+ cation among large pools of the co-existent different anions or metal cations, respectively, revealing that 1 could be used as a potential dual functional fluorescent sensor for trace amounts of the chromate anions or Fe3+ cation. The detection limits obtained through the incremental fluorescence quenching titration experiments reach to sub-ppm level for the Cr(VI) anions (CrO42−/Cr2O72−) and Fe3+ cation, respectively.