We have investigated the mechanosynthesis of a series of second-sphere salts, guest⊂[H2L]2+·[MCl4]2– [L = N,N′-dibenzyl-(±)-trans-1,2-diaminocyclohexane], and the reversible transformations to their chelating coordination complexes [MCl2(L)] through dehydrochlorination reactions. The second-sphere salts and their corresponding coordination complexes show different solid-state fluorescence spectra. The complex ZnCl2(L) (2′) acts as a sensor for the highly sensitive detection of nitroaromatic compounds through fluorescence quenching.

The effect of the withdrawing ability of –CF3 groups in a large and flexible bidentate ligand has been evaluated by monitoring the course of solid-state dehydrochlorination reactions. We demonstrate that the coordination bond formation does not occur by mechanochemical means from a second coordination sphere adduct. Quantum mechanical calculations have shown that frontier molecular orbital energy and net charges at N centers can justify the less reactive nature of the partially fluorinated ligand, corroborating the experimental results.

We report a type of highly efficient deep-red light-emitting diode based on type-II CdTe/CdSe core/shell quantum dots (QDs). High-quality CdTe/CdSe core/shell QDs with three different photoluminescence emissions peaked at 642, 664 and 689 nm are, respectively, synthesized through a green process. Correspondingly, three devices employing QDs with different PL peaks show the maximum external quantum efficiency (EQE) of 5.24%, 5.74% and 6.19% with a low turn-on voltage of about 1.8 V, respectively. Interestingly, EQE is kept above 5% in a certain range of luminance (from 101 to 103 cd m−2). To our knowledge, this is the first report that uses type-II core/shell QDs as deep-red emitters and these results may offer a practicable reference for applications that require a high efficiency deep-red illuminant.

Here, we report the influence of the ambient gas on the performance of quantum dot-based light-emitting diodes (QD-LEDs). The blue QD-LED devices with the maximum external quantum efficiency of 8.1% and the turn-on voltage of 2.7 V could be obtained in air. The efficiency decreases by 12% and turn-on voltage increases by 0.3 V relative to the control devices fabricated in a N2-filled glovebox. The histogram of maximum external quantum efficiency (EQE) shows average peak EQE of 8.08% and a low standard deviation of 3.63%, suggesting high reproducibility. Correspondingly, the operational lifetime of 376 h is obtained, which is on par with 408 h of devices fabricated in N2. For the devices fabricated in air, relatively high efficiency could be maintained only at low voltages, because of the near balanced injection of carriers under low bias. The measurements of contact potential difference, chemical composition, and surface roughness are used to verify the variation of energy level and surface morphology of films influenced by different ambient gas. These results would offer reasonable guidance for the application of QD-LEDs in actual large-scale production.Keywords: ambient gas; blue emission; electroluminescence; light-emitting diodes; quantum dot

Hydrated solid salt of tris(hydroxymethyl)aminomethane (THAM) and sulfosalicylic acid (SA) undergoes a facile solid-state dehydration process upon heating, in which single crystals of the hydrated phase transform to a microcrystalline powder of an anhydrous product phase. The structural properties of the anhydrous phase have been determined directly from powder X-ray diffraction data, allowing rationalization of the structural changes associated with the dehydration process. The dehydration process is associated with substantial reorganization of the hydrogen bonding arrangement, while most hydrogen bonds related to SA ion are actually preserved in the transformation.

Second-sphere coordination refers to any intermolecular interaction with the ligands directly bound to the primary coordination sphere of a metal ion. In this article, we have successfully applied the second-sphere coordination approach in the construction of versatile host frameworks that can accommodate various guest molecules. We have used a family of bidentate flexible molecules as second-sphere ligands, and the tetrachlorometalate anion [MCl4]2– (where M = Cu, Co, Cd, Zn, and Hg) as the primary coordination sphere to synthesize new second sphere adducts. By introducing an alkyl spacer −(CH2)n– (n = 1, 2, 3, 4) to bibenzylamine (L0), the ligands L1, L2, L3, and L4 with higher degree of flexibility were synthesized. Different guest molecules such as alcohol, acetic acid, acrylic ester, or acetonitrile can be included in the host framework self-assembling diprotonated L1–L4 and [MCl4]2–, leading to a novel type of supramolecular assemblies: CH3CH2OH⊂[L2]2H+·[CuCl4]2– (2), CH3OH⊂[L3]2H+·[MCl4]2– (3), CH3COOH⊂[L3]2H+·[CuCl4]2– (4), CH2CHCOOCH3⊂[L3]2H+·[MCl4]2– (5–7), CH3CN·H2O⊂[L4]2H+·[MCl4]2– (8–9), and CH3OH⊂[L4]2H+·[MCl4]2– (10). L2 forms the quasi-chelating charge-assisted N–H···Cl hydrogen bonds with [MCl4]2– that can transform in the solid-state to a chelated coordination complex following a mechanochemical dehydrochlorination reaction. By increasing the number of methylene groups, ligands L3 and L4 exhibit considerable conformational diversity due to the higher flexibility induced by the backbone chains. The −(CH2)n– spacer lengths of the ligands influences the structural dimensionality, and its solid-state mechanochemical reactivity preventing the transformation from salt [L3–4]2H+·[MCl4]2– to the chelating coordination complex [(MCl2)(L3–4)]. Moreover, the thermal stability of the second sphere adducts has been monitored by thermogravimetric analyses and X-ray powder diffraction (PXRD). We demonstrate that some of the second sphere adducts are dynamic, showing reversible guest release/uptake involving crystalline-to-amorphous-to-crystalline phase transformations. Quantum\Mechanical (QM) demonstrate that ligands with backbone lengths longer than −(CH2)2– are reticent to react via dehydrochlorination reaction because of the backbone chain length, the symmetry and orientation of the frontier molecular orbitals (FMOs), while for the −(CH2)2–, the length and orientation of the FMOs is optimal for the reaction to occur.

A family of isostructural, chiral supramolecular networks have been obtained in the solid state by exploiting second sphere coordination interactions in the self-assembly of achiral tris amines L1 and L2 with tetrahalometallate and halide ions. Quantum-Mechanical (QM) calculations specific for solid phases provided additional insights into the intramolecular and packing interactions which determine chirality, pointing to a direct effect of the methyl groups of the central benzene ring.

•Violet cadmium-free quantum dot-based light-emitting diodes (QD-LEDs) were demonstrated.•The performance of QD-LEDs was optimized by selecting the hole transport materials.•Violet QD-LEDs with high efficiency and low turn-on voltage could be obtained via controlling the amount of TFB mixed PVK.•No obvious broad emission could be recorded in all the regions of the EL spectrum of TFB–PVK mixture HTL devices.Bright and efficient violet quantum dot (QD) based light-emitting diodes (QD-LEDs) with heavy-metal-free ZnSe/ZnS have been demonstrated by choosing different hole transport layers, including poly(4-butyl-phenyl-diphenyl-amine) (poly-TPD), poly[9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine] (TFB), and poly-N-vinylcarbazole (PVK). Violet QD-LEDs with maximum luminance of about 930 cd/m2, the maximum current efficiency of 0.18 cd/A, and the peak EQE of 1.02% when poly-TPD was used as HTL. Higher brightness and low turn-on voltage (3.8 V) violet QD-LEDs could be fabricated when TFB was used as hole transport material. Although the maximum luminance could reach up to 2691 cd/m2, the devices exhibited only low current efficiency (∼0.51 cd/A) and EQE (∼2.88%). If PVK is used as hole transport material, highly efficient violet QD-LEDs can be fabricated with lower maximum luminance and higher turn-on voltages compared with counterpart using TFB. Therefore, TFB and PVK mixture in a certain proportion has been used as HTL, turn-on voltage, brightness, and efficiency all have been improved greatly. The QD-LEDs is fabricated with 7.39% of EQE and 2856 cd/m2 of maximum brightness with narrow FWHM less than 21 nm. These results represent significant improvements in the performance of heavy-metal-free violet QD-LEDs in terms of efficiency, brightness, and color purity.

We have applied crystal engineering as a tool to study the solid-state transformation from molecular salts to coordination complexes via mechanochemical dehydrochlorination reactions. The −(CH2)n– (n = 2, 3) alkyl chains were introduced into the bibenzylamine moiety to form the two nitrogen bases N,N,N′,N′-tetrabenzylethylenediamine (L1) and N,N,N′,N′-tetrabenzylpropydiamine (L2), which were self-assembled with tetrachlorometalates to form a series of supramolecular salts through second-sphere coordination. Single crystals of salts [L1]2H+·[CuCl4]2–·solvent (1) and [L2]2H+·[XCl4]2–·solvent (2–4; X = Cu, Hg, Zn) were obtained and their structures determined by single-crystal X-ray diffraction. The effect of different alkyl chains (two and three −CH2– units) on the solid-state reactivity showed that the chelating complexes resulting from the mechanochemical dehydrohalogenation reaction depend on the formation of quasi-chelating hydrogen-bonding salts. Quantum-mechanical calculations have been used to gain insight in this mechanochemical dehydrohalogenation reaction, demonstrating that not only is size matching between reactants is important but also conformational energies, intermolecular interactions, and the symmetry of frontier molecular orbitals play an important role.

We report three molecular salts formed by 5-sulfosalicylic acid dihydrate (A·2H2O) and 4,4′-diaminodiphenylmethane (B) in different stoichiometric ratios. The A1B1·H2O, A1B2 and A2B1·H2O molecular salts can be accessed via mechanochemical grinding and from solution. Structural aspects were analyzed using single crystal and X-ray powder diffraction (XRPD). The reversible solid state ionic interconversion between A1B1·H2O, A1B2, and A2B1·H2O upon neat grinding by adding an appropriate amount of A·2H2O or B is described. In the ionic interconversion water molecules are included or excluded upon grinding, which suggests that water plays an important role in the proton transfer. The solid-state fluorescence spectra of A1B1·H2O, A1B2, and A2B1·H2O showed that the three molecular salts exhibit emission features and are red-shifted compared with the starting materials A·2H2O and B. The interparticle (CT) interactions and the degree of anion deprotonation are important in the solid-sate fluorescence of the described molecular salts. The photoluminescence experimental results have been corroborated using time-dependent density functional theory (TD-DFT), which has been shown to provide reasonable results for the excited states of molecules involved in the formation of the molecular salts.

In this paper, we have used the hydrogen-bonding interactions, combining the designed diamine ligands and anionic metal chlorides, into the construction of a series of new pillar-layered supramolecular complexes. The flexible molecule N,N,N′,N′-tetra-p-methoxybenzyl-ethylenediamine (L1) bearing doubly protonated H-bond donors, has been synthesized and reacted with the metal chlorides (such as [PdCl4]2−, [FeCl4]− and [CoCl4]2−) via weak C–H···Cl interactions, yielding crystal products [H2L1]2+·Cl−·[FeCl4]− (1), 0.5H2O ⊂ [H2L1]2+·Cl−·0.5[PdCl4]2− (2) and [2-hydroxy naphthyl]1.5 ⊂ 2[H2L1]2+·2Cl−·[CoCl4]2− (3). The 3-D networks are organic double layers formed by the self-assembly of the ligands through extensive hydrogen-bonding interactions (C–H···O or C–H···π interactions) and further interconnected by [PdCl4]2−/[FeCl4]−/[CoCl4]2− in a pillar fashion, constructing into pillar-layered networks with channels accessible to various guest molecules. The inclusion property of [H2L1][CoCl4] was studied, varieties of guest molecules, such as 2-hydroxy naphthyl, phenanthrene and hydroquinone, can be included in the framework.

The compound tribenzylamine (TBA) and its derivatives are a type of classical tripodal ligands in building up diversity of supramolecular arrays or networks. In the present contribution, we described two new supramolecular complexes 2[C21H22N+]·[CoCl4]2−·(1) and 2[C21H22N+]·[CuCl4]2− (2) by reacting protonated TBA with CoCl2·6H2O/CuCl2·2H2O. Different from previous TBA supramolecular complexes, these two supramolecular complexes were easier to obtain by grinding protonated TBA and CoCl2·6H2O/CuCl2·2H2O in an agate mortar than using conventional solution method. The two supramolecular complexes form fascinating 3D helical architectures, with two types of interwoven helical chains involved inside the structures. A comparison of the geometries of TBA in these two supramolecular complexes with the previously reported TBA supramolecular complexes shows that the significant differences are due to the conformation of the three arms of phenyl rings around the N center.

In this study, we have deliberately utilized the second-sphere coordination approach into the construction of supramolecular inclusion solids Cl ⊂ [H2L1]·[InCl4] (Crystal I) and Br ⊂ [H2L1]·[TeBr6] (Crystal II). The chloride or bromine anions can be encapsulated inside the host assemblies formed by the diamine molecule (4,6-dimethyl-1,3-phenylene) bis(N,N-dibenzylmethane) (L1) and the metal complexes ([InCl4]− and [TeBr6]2−) via second-sphere interactions. The inclusion complexes have been structurally characterized by X-ray crystallography, indicating that weak C–H···Cl and C–H···Br hydrogen bonding synthons play a significant role in the construction of host framework. 2-D networks are formed in both complexes by the interconnection of 1-D networks through the multiple weak hydrogen bonding interactions with [InCl4]− or [TeBr6]2−. The guest Cl− or Br− anions are encapsulated inside the host cages through N–H···Cl hydrogen bonds. The inclusion selectively was studied for the two host assemblies.

In this paper, we have built up the organic-inorganic hybrid co-crystal (1) by using the derivative of ethylenediammonium cations (N,N,N′,N′-tetra-p-methoxybenzyl-ethylenediamine, L1) and [CuCl4]2− anions. The reaction was carried out by mixing MeOH solution of CuCl2·2H2O and HCl/MeOH solution of L1 at room temperature. Two types of inclusion compounds can be formed when using different guest molecules. When guest molecules, such as anthracene or phenanthrene, were included, it resulted in the formation of interlayered structures: anthracene ⊂ [H2L1]2+·[CuCl4]2− (2) and phenanthrene ⊂ [H2L1]2+·[CuCl4]2− (3). When β-naphthyl phenol were included, it led to the formation of pillared-layered complexes of [1-chloride-β-naphthyl phenol]1.0·[β-naphthyl phenol]0.5·[methanol]1.0 ⊂ 2[H2L1]2+·2Cl−·[CuCl4]2− (4).

We have presented herein the utilization of second sphere coordination approach to construct supramolecular inclusion solids with varieties of guest molecules. Two distinct types of host frameworks were constructed by cobalt chloride anion ([CoCl4]2− or [Co2Cl6]2−) and diprotonated N-bidentate ligand L1 (N,N,N′,N′-tetra-p-methylbenzyl-ethylenediamine) or chloride anion-directed L1. The pillared double - layered host framework constructed by cobalt chloride anion ([CoCl4]2− or [Co2Cl6]2−) and chloride anion-directed L1 can encapsulate o-hydroxybenzaldehyde and p-hydroxybenzaldehyde molecules, leading to the formation of supramolecular inclusion solids: {[C7H6O2]1.5·[CH4O]0.5} ⊂ {[L1]2·4H+·2Cl−·[CoCl4]2−} (1) and {[C7H6O2]0.5·[CH4O]0.25} ⊂ {[L1]·2H+·Cl−·[Co2Cl6]0.52−} (2); whereas the channel-cave host framework constructed by [CoCl4]2− and L1 can include acetic acid molecules, leading to the formation of supramolecular inclusion solid [C2H4O2]2 ⊂ {[L1]·2H+·[CoCl4]2−} (3).

The effect of the withdrawing ability of –CF3 groups in a large and flexible bidentate ligand has been evaluated by monitoring the course of solid-state dehydrochlorination reactions. We demonstrate that the coordination bond formation does not occur by mechanochemical means from a second coordination sphere adduct. Quantum mechanical calculations have shown that frontier molecular orbital energy and net charges at N centers can justify the less reactive nature of the partially fluorinated ligand, corroborating the experimental results.

A family of isostructural, chiral supramolecular networks have been obtained in the solid state by exploiting second sphere coordination interactions in the self-assembly of achiral tris amines L1 and L2 with tetrahalometallate and halide ions. Quantum-Mechanical (QM) calculations specific for solid phases provided additional insights into the intramolecular and packing interactions which determine chirality, pointing to a direct effect of the methyl groups of the central benzene ring.

We report a type of highly efficient deep-red light-emitting diode based on type-II CdTe/CdSe core/shell quantum dots (QDs). High-quality CdTe/CdSe core/shell QDs with three different photoluminescence emissions peaked at 642, 664 and 689 nm are, respectively, synthesized through a green process. Correspondingly, three devices employing QDs with different PL peaks show the maximum external quantum efficiency (EQE) of 5.24%, 5.74% and 6.19% with a low turn-on voltage of about 1.8 V, respectively. Interestingly, EQE is kept above 5% in a certain range of luminance (from 101 to 103 cd m−2). To our knowledge, this is the first report that uses type-II core/shell QDs as deep-red emitters and these results may offer a practicable reference for applications that require a high efficiency deep-red illuminant.