Shuquan Zhang

Beryllium-free Li4Sr(BO3)(2) for deep-ultraviolet nonlinear optical applications

Nonlinear optical (NLO) materials are of great importance in laser science and technology, as they can expand the wavelength range provided by common laser sources. Few NLO materials, except KBe2BO3F2 (KBBF), can practically generate deep-ultraviolet coherent light by direct second-harmonic generation process, limited by the fundamental requirements on the structure-directing optical properties. However, KBBF suffers a strong layering tendency and high toxicity of the containing beryllium, which hinder the commercial availability of KBBF. Here we report a new beryllium-free borate, Li4Sr(BO3)2, which preserves the structural merits of KBBF, resulting in the desirable optical properties. Furthermore, Li4Sr(BO3)2 mitigates the layering tendency greatly and enhances the efficiency of second-harmonic generation by more than half that of KBBF. These results suggest that Li4Sr(BO3)2 is an attractive candidate for the next generation of deep-ultraviolet NLO materials. This beryllium-free borate represents a new research direction in the development of deep-ultraviolet NLO materials.

A multi-metal-cluster MOF with Cu4I4 and Cu6S6 as functional groups exhibiting dual emission with both thermochromic and near-IR character

Two classical metal clusters, CuI4I4 and CuI6S6, are introduced as functional connecting nodes to construct a novel multi-metal-cluster MOF [(CuI4I4)3(CuI6)2(3-ptt)12]n·24nDEF·12nH2O (1) that incorporate their inherent luminescent properties, induced by their respective metal–metal interactions. These two distinct clusters are combined together for the first time to perform as functional luminophores that display unusual dual emission with both thermochromic luminescence and near-infrared (NIR) character.

Solid‐State Reversible Quadratic Nonlinear Optical Molecular Switch with an Exceptionally Large Contrast

Exceptional nonlinear optical (NLO) switching behavior, including an extremely large contrast (on/off) of ∼35 and high NLO coefficients, is displayed by a solid-state reversible quadratic NLO switch. The favorable results, induced by very fast molecular motion and anionic ordering, provides impetus for the design of a novel second-harmonic-generation switch involving molecular motion.

Highly selective carbon dioxide adsorption in a water-stable indium–organic framework material

A metal-organic framework, with chiral 4(1) In(OH)(CO(2))(2) helix chains, exhibits a high CO(2) uptake under ambient conditions and outstanding selective separations of CO(2) from CH(4) or N(2). Its high stability toward humidity or even boiling water is confirmed by PXRD method.

Effective visible-light driven CO2 photoreduction via a promising bifunctional iridium coordination polymer

A promising coordination polymer photocatalyst (Y[Ir(ppy)2(dcbpy)]2[OH]) (Ir-CP, ppy = 2-phenylpyridine, dcbpy = 2,2′-bipyridine-4,4′-dicarboxylate) based on a highly efficient light-harvesting Ir unit, Ir(ppy)2(Hdcbpy), has been obtained, with good stability and exhibiting visible-light absorption over a broad range, arising from the metal-to-ligand charge transfer (3MLCT) and ligand-to-ligand charge transfer (LLCT). The designed Ir-CP heterogeneous photocatalyst acts as both a photosensitizer to harvest visible light, and an active catalyst for CO2 photoreduction. Due to the broad absorption in the UV-visible region and long-lived excited states of Ir-CP, the photocatalyst can efficiently catalyze CO2 reduction under visible-light irradiation in a heterogeneous photocatalytic system. For the first time, the remarkable photocatalytic efficiency of Ir-CP under visible-light irradiation (38 μmol HCOO− was produced in 6 h) was shown. Moreover, Ir-CP shows high photostability during CO2 photoreduction, which promotes the recyclability of the heterogeneous photocatalyst.

An intensely luminescent metal-organic framework based on a highly light-harvesting dyclo-metalated iridium(III) unit showing effective detection of explosives.

An intense visible yellow-orange emission with long lifetime and enhanced quantum yield has been achieved for a metal-organic framework based on a highly light-harvesting dyclo-metalated iridium(III) unit, which shows effective detection of nitroaromatic explosives on the ppm scale.

Ferroelastic phase transition and switchable dielectric behavior associated with ordering of molecular motion in a perovskite-like architectured supramolecular cocrystal

An organic supramolecular co-crystal with a perovskite-like architecture, dabco·p-nitrophenol (1, dabco = 1,4-diazabicyclo[2.2.2]octane), which undergoes a reversible ferroelastic phase transition with the Aizu notation of 2/mF at around 128 K (Tc), displays switchable dielectric behaviors triggered by the ordering of molecular rotational motion in the dabco moieties. Its transition dynamic behaviors were investigated by variable-temperature crystal structure analysis, thermal analysis and dielectric measurements. The results reveal that in the high-temperature state, 1 behaves as a molecular rotor, in which the dabco moiety rotates around the N⋯N axis as a rotator, and the neutral p-nitrophenol part acts as a stator jointed through the intermolecular N–H⋯O H-bonds. Below the Tc, the rotational motions of the rotator are frozen and the whole setup becomes much more ordered, corresponding to its low-temperature stable phase. Moreover, study of the deuterated analogue of 1 excludes the possibility of proton movement along N–H⋯O bonds as the microscopic origin of the phase transition. The findings provide a useful strategy to explore a new class of compounds exhibiting distinct switchable dielectric performances for application in the ferroic-related field.

N-Isopropylbenzylammonium tetrafluoroborate: an organic dielectric relaxor with a tunable transition between high and low dielectric states

An organic dielectric relaxor, N-isopropylbenzylammonium tetrafluoroborate (1), with tunable dielectric properties between high and low dielectric states, has been successfully constructed through the prominent strategies of reversible structure transitions associated with ordering and reorientation of molecular motions. 1 undergoes an exceptional order–disorder solid state phase transition at 201 K, which was confirmed by the variable temperature single crystal X-ray diffraction analysis, thermal analysis and dielectric measurements. Owing to the ordering of the pendulum-like motion of methyl groups in the N-isopropylbenzylammonium (N-IPBA) cations and the reorientation of the molecular dipoles, 1 demonstrates a phase transition from a space group of C2/m at room temperature to C2/c at low temperature. Emphatically, the striking anisotropy of the dielectric response was investigated, revealing the crucial role of the ordering and orientation motions of N-IPBA cations. Moreover, the significant dielectric relaxation behaviour, attributed to the orientational polarization of the molecules’ dipoles, was observed and discussed. Such distinctive dielectric performances suggest that 1 might be a potential switchable relaxor-type dielectric material.

Construction of Interpenetrated Ruthenium Metal–Organic Frameworks as Stable Photocatalysts for CO2 Reduction

Poor stability has long been a major obstacle to the practical applications of metal-organic framework (MOF) photocatalysts. This problem can be overcome by the use of structural interpenetration. In this work, by modifying Ru metalloligands, we have rationally designed two Ru-polypyridine based MOFs (with non-interpenetrated and interpenetrated structures, respectively), both of which exhibit similar photocatalytic activities for CO2 photoreduction. Remarkably, the interpenetrated Ru-MOF possesses good photocatalytic durability and recyclability, and shows much higher thermal and photic stability in comparison with its non-interpenetrated counterpart. To the best of our knowledge, this is the first time that the stability of MOF photocatalysts was improved by using structural interpenetration.

A new UV nonlinear optical material CsZn2B3O7: ZnO4 tetrahedra double the efficiency of second-harmonic generation.

A new noncentrosymmetric borate CsZn2B3O7 was synthesized by the solid-state reaction techniques. The crystals were obtained by flux method and are of block shape without layering tendency. Single-crystal X-ray diffraction analysis reveals that the crystal structure is composed of [Zn2BO5]∞ two-dimensional layers that are bridged by [B3O6](3-) groups to form a three-dimensional framework with one-dimensional channels occupied by Cs(+) cations along the a and c axes. Thermal analysis indicates that CsZn2B3O7 melts incongruently. UV-visible-near-IR diffuse reflectance spectrum gives a short absorption edge at 218 nm. CsZn2B3O7 is phase-matchable, with a powder second-harmonic generation (SHG) efficiency of 1.5 × KDP (KDP, potassium dihydrogen phosphate) at 1064 nm, based on the Kurtz-Perry method. These results show that CsZn2B3O7 may have prospects as a UV nonlinear optical material. Interestingly, the SHG efficiency of CsZn2B3O7 is about twice that of γ-KBe2B3O7, a structurally analogous alkaline and alkaline earth borate. First-principles calculations combined with atom-cutting analysis reveal that the ZnO4 tetrhedral groups in CsZn2B3O7 account for the SHG enhancement.