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The development of stimulus-responsive luminescent materials, especially those based on a single compound exhibiting multicolor and high-contrast (Δλem ≥ 100 nm) chromic properties, is a critical challenge. In this work, we synthesized and characterized a zinc(II) complex (1). As expected, 1 displays aggregation-induced emission enhancement (AIEE) in THF/H2O mixtures, and remarkable multicolor switching under external stimuli in the solid state. Complex 1 shows reversible mechanochromic luminescence behavior with a large wavelength shift (Δλem = 100 nm) during the grinding–fuming cycles, due to the phase transformation between the crystalline and amorphous states. More impressively, 1 exhibits obvious acidochromic properties (Δλem = 130 nm) which originate from the adsorption of vapor and a gas–solid reaction on the crystal surface. Furthermore, 1 exhibits electrochemical oxidation behavior accompanied by quenching of yellow-green emission due to the overlap of an emission band and an absorption band. The above-mentioned color changes under ambient light can also be observed by the naked eye during the mechanical, acid–base vapor and electrical stimulation. Based on the high-contrast and multicolor switching, complex 1 was successfully developed into test papers and films in the field of rapid detection of mechanical stimuli and HCl/NH3 vapors. [ABSTRACT FROM AUTHOR]

Materials exhibiting mechanoluminescence (ML) are a class of smart materials capable of mechanical-to-light energy conversion. Thus, ML materials have been widely used in various electronic applications such as smart sensors, security systems, human–machine interfaces, and energy harvesting systems. Herein, we report a centrosymmetric ML semiconductor host material family MGa2S4 (M = Ca, Sr), which features in-layered structures constructed with unique distorted bi-tetrahedral [Ga2S2S4/2] lattice units. It exhibited similar structural characteristics to the well-known ML semiconductor host ZnS. Remarkably, the lanthanide ions of 5d → 4f transition-activated hosts showed sensitive and high ML luminance under natural lighting upon mechanical stimulation; thus, an efficient mechanical-to-light energy conversion of a self-powered display was achieved. Moreover, because of structural distortion and strain-gradient-induced electrical polarization in the ML host material upon mechanical stimulation, a ML mechanism based on the synergy effect between local electronic polarization and flexoelectricity was proposed. This study facilitates a deeper understanding of the relationship between the structure and underlying ML, and promotes further development of ML-material-based products and technologies. [ABSTRACT FROM AUTHOR]

Multifunctional luminescent materials have attracted intensive interest. However, the mechanisms behind them are still to be explored. In this work, three Zn(II) complexes based on Schiff bases (HL1 and HL2) that contain rotatable aromatic rings were designed and prepared. They exhibited different mechanochromic luminescence (MCL) and acidochromism. The polymorphous ZnL12 and ZnL1a2 crystallize in different crystal systems with different conformations. The ligands in ZnL12 adopt a more twisted conformation than those in ZnL1a2. ZnL12 exhibits MCL with high contrast, while ZnL1a2 exhibits a negligible MCL property. This may be due to the looser packing of the complex induced by the more twisted conformation of the ligand HL1. ZnL12 could undergo crystal phase transformation into ZnL1a2 by grinding/fuming cycles. To increase the flexibility of the ligand, a methylene group was introduced to result in HL2, which can improve the mechanochromic luminescence effect of the Zn(II) complex with high color contrast. The ligands involved in coordination generally adopt a more twisted conformation than those free ligands due to the steric hindrance, resulting in more obvious MCL for complexes. By comparing the luminescence of ligands and their complexes under acid–base stimulation, it is found that the acidochromic properties could be attributed to the generation of ligands at the surface of complexes via the gaseous HCl-solid Zn(II) complex reaction. The high contrast mechanochromic and acidochromic luminescence properties would lead to promising potential applications of these complexes in smart fluorescent materials, and would also provide some ideas for the design of multi-stimuli responsive molecules. [ABSTRACT FROM AUTHOR]

A multi-binding site chemosensor, N-(3-methoxy-2-hydroxybenzylidene)-3-hydroxy-2-naphthahydrazone (H3L), with excited-state intramolecular proton transfer (ESIPT) behaviour was prepared and characterized. It possesses no aggregation-induced emission (AIE) characteristics but can detect Cd2+ and Zn2+ ions selectively in the "off–on" mode based on the AIE of their complexes in the media of THF/HEPES and THF/H2O, respectively, which will provide a new strategy for target detection based on AIE. The detection limits of Zn2+ and Cd2+ were 9.85 × 10−9 M and 1.27 × 10−7 M, respectively. The aggregates of the complexes formed in the detection system were confirmed by DLS data and SEM images. The corresponding Zn2+ (1) and Cd2+ (2) complexes were prepared to investigate the response mechanism. Powder X-ray diffraction and single crystal X-ray diffraction proved that complex 1 is the species formed in the detection system. The chemosensor coordinates with the Cd2+ and Zn2+ ions in different formation and coordination modes, leading to the emission position of the aggregates at 560 and 645 nm, respectively, based on which Cd2+ ions were successfully differentiated from Zn2+ ions. Moreover, the detection of Cd2+ and Zn2+ ions was realized qualitatively via test paper and quantitatively in water. [ABSTRACT FROM AUTHOR]

Five novel coordination polymers (CPs), formulated as {[Co3(μ4-cpboda)2(μ1,1-OH2)2(2,2-bipy)2]·1.5DMF·2H2O}n (1), {[Co3(μ3-cpboda)2(4,4′-bpy)3(H2O)2]·4H2O}n (2), {[Co(μ2-H2cpboda)2(1,4-bib)3(H2O)2]·H2O·DMF·1.5HCOOH}n (3), [Cd(μ3-Hcpboda)(1,4-bib)]n (4), and {[Cd3(μ4-cpboda)2(μ1,1-OH2)2(phen)2]·2DMF·1.5H2O}n (5) (H3cpboda = 3,3′-((5-carboxy-1,3-phenylene)bis(oxy))dibenzoic acid, 2,2-bipy = 2,2-bipyridine, 4,4′-bpy = 4,4′-bipyridine, 1,4-bib = 1,4-di(1H-imidazol-1-yl)benzene, phen = 1,10-phenanthroline) have been synthesized under solvothermal conditions and characterized by elemental analyses (EAs), single-crystal X-ray diffraction analyses, X-ray powder diffraction analyses (PXRD), FT-IR spectra, and thermogravimetric analyses (TGAs). The structural analyses reveal that these complexes have four 2D coordinate polymers and one 3D framework, in which metal ions are in octahedral coordination geometries in 1–3 and 5, but seven-coordinated disordered pentagonal bipyramids in 4. Complexes 1 and 5 represent linear trinuclear [M3(μ1,1-OH2)2(μ1,3-COO)4] SBUs in 1 (M = Co(ii)) and in 5 (M = Cd(ii)) based on a 3,4,6-connected net with a point symbol (32·4)2(32·83·9)2(34·42·82·94·103) net, complex 2 exhibiting a (3-c)2(4-c)(4-c)2 3D structure with the (52·6·82·9)2(52·62·92)(52·6)2 topology and complexes 3 and 4 having a novel 2D framework with the point symbol of (44·62). Magnetization analyses disclose the antiferromagnetic (AF) behaviors between Co(ii) ions in complexes 1 & 3 and S = 3/2 (Co2+) spin Heisenberg chains with alternating magnetic sequences (F/F/AF)n in 2. Fluorescence measurements indicate that 4 and 5 are promising luminescence sensors for the detection of CrO42− and Cr2O72− anions in aqueous solution. [ABSTRACT FROM AUTHOR]

Developing high-performance electrode materials to replace a traditional graphite electrode is critical for the commercialization of lithium ion batteries, which however still remains a great challenge. Herein, we report a suitable method to synthesize a series of well-dispersed nanostructured Co3O4–CoFe2O4 composites (CCFs) from bimetallic metal–organic frameworks (BiMOFs) with varied Fe3+/Co2+ molar ratios. When used as anodes for lithium ion batteries, the CCF-12 composite exhibits a maximum initial discharge capacity of 1328 mA h g−1, a reversible capacity of 940 mA h g−1 at 100 mA g−1 after 80 cycles, and a better rate capability in comparison with those of pure Co3O4 and other CCF composites. The well-dispersed structure and small particle size are believed to mainly contribute to the outstanding electrochemical performance of CCF-12 electrodes. [ABSTRACT FROM AUTHOR]

A tetraphenylethene (TPE)-decorated tripodal tris(urea) ligand L was synthesized, which shows large emission enhancement when binding to an orthophosphate anion (PO43−), but exhibits only weak or no fluorescence with other anions. The anion-binding and fluorescence properties were studied by X-ray crystal structure, NMR and fluorescence spectroscopy, and by DFT computations and the results demonstrate that the different fluorescence performance may be determined by the anion-binding modes (i.e., full- or half-encapsulation). [ABSTRACT FROM AUTHOR]

A Type I porous liquid based on the mixed-linker zeolitic imidazolate framework, ZIF-8/90-PL, has been prepared by a one-step imine condensation reaction and characterized by X-ray diffraction, FT-IR spectroscopy, TGA and rheology analysis. This facile preparation strategy of a porous liquid has enormous industrial production and application potential, with over one kilogram of ZIF-8/90-PL being successfully prepared. ZIF-8/90-PL can be directly used as a liquid absorbent or be co-processed with alumina hollow fibers to form a composite membrane with improved selectivity in the context of CO2 separation from CH4 or N2. This simple synthesis method is expected to be extended to other metal–organic frameworks. [ABSTRACT FROM AUTHOR]

A multi-level regulation of fluorescence enhancement upon anion coordination and subsequent binding of a guest (methyl viologen) was presented by a bis–bis(urea)-decorated tetraphenylethene (TPE) ligand with an assembly-enhanced emission characteristic. [ABSTRACT FROM AUTHOR]