Guangfeng Liu

Bulk crystal growth of hybrid perovskite material CH3NH3PbI3

Organic–inorganic hybrid perovskite materials have been receiving considerable attention due to their promising applications in many optoelectronic fields. However, some of the fundamental properties of perovskite materials are still disputed, because most of them are derived from a thin-film state. To comprehend the intrinsic characteristics in a single crystal, herein we report, for the first time, the bulk crystal growth of CH3NH3PbI3. Single crystals of tetragonal CH3NH3PbI3 with dimensions of 10 mm × 10 mm × 8 mm were grown by a temperature-lowering method in HI solution. Studies in to the refinement and orientations of the CH3NH3PbI3 single crystal structure were conducted based on a high quality crystal. The absorption edge of a CH3NH3PbI3 single crystal was located at about 836 nm, indicating that the band gap of CH3NH3PbI3 is approximately 1.48 eV, which is close to the theoretical results and smaller than those derived from polycrystalline and thin-films. CH3NH3PbI3 crystal exhibits a relatively wide absorption (from 250 nm to 800 nm) and a relatively good thermal stability.

Oriented Single-Crystal-to-Single-Crystal Phase Transition with Dramatic Changes in the Dimensions of Crystals

We report here a new polymorph of cocrystal CuQ2-TCNQ that shows an oriented single-crystal-to-single-crystal phase transition along its a-axis at ambient conditions. Upon mechanical stimulation, it converts into another polymorph accompanied by almost doubling its length and halving its thickness. Our crystallographic studies indicate the dramatic changes in crystal dimensions resulted from the prominent changes of molecular stacking patterns. A reasonable mechanism for the phenomenon was proposed on the basis of the structural, microscopic, and thermal analysis.

The effect of mechano-stimuli on the amorphous-to-crystalline transition of mechanochromic luminescent materials

Mechanochromic luminescence via grinding-induced crystalline-to-amorphous transition in some organic materials has been well illustrated in recent years. Here, we focus on the luminescence reversion process induced by thermal annealing crystallization of a series of tetraphenylethene analogues. Through paired comparisons, we disclosed that the mechano-stimuli can not only destroy the crystallinity of crystalline materials but can also bring a significant effect on the amorphous-to-crystalline transition of amorphous materials. That is, only when an amorphous material underwent mechano-stimuli can it crystallize by thermal annealing to recover its emission. This grinding-facilitated annealing crystallization is rationalized to originate from the twisted and rotatable intramolecular conformation that can be altered by mechano-stimuli. Besides some special usage of the material as security paper or latent memory medium, the study presents new strategies to control the crystallization of organic semiconductors.

In Situ Microscopic Observation of the Crystallization Process of Molecular Microparticles by Fluorescence Switching

To clearly understand the solid-state amorphous-to-crystalline transformation is a long-standing challenge because such crystallization occuring in confined environments is difficult to observe directly. We developed an in situ and real-time imaging procedure to record the interface evolution in a solid-state crystallization of molecular amorphous particles. The method, by employing a tetra-substituted ethene with novel morphology-dependent fluorescence, which can distinguish the interfaces between the crystalline and amorphous phase by fluorescence color, is a simple and practical method to probe the inner process of a molecular microparticle. The crystallization of amorphous microparticles in different cases was clearly recorded, where the perfect microparticles and those with defects demonstrate diverse destinies. The details disclosed in this observation will deepen the understanding for a series of solid-state crystallization that we know little about before.

Structural features and optical properties of a carbazole-containing ethene as a highly emissive organic solid

Carbazole derivatives are versatile materials especially for optoelectronic applications in light of their activity in both electronics and optics. To suppress the luminescence quenching effect in the condensed phase, we constructed a carbazole derivative with aggregation-induced emission characteristics. The highly emissive organic solid of carbazole-substituted ethene was facilely prepared and thoroughly tested. Through inspection of the geometric structure and packing motifs of the crystalline materials, the severely twisted conformation and the absence of strong intermolecular π–π interactions are found to account for the extremely high solid-state quantum yield. The highly blue emissive crystal fibers exhibit optical waveguide properties. Electroluminescence (EL) studies reveal the hole-transporting nature of the material.

Mechanochromic luminescence of fluorenyl-substituted ethylenes.

It has been reported several times that some organic luminogens with aggregation-induced emission (AIE) characteristics exhibit the abnormal phenomenon of crystallization-induced blueshift fluorescence, which makes them suitable for utilization as luminescence color-switching materials. Because of the attractive application potential and the numerous underlying structure-property relationships in such materials, we investigated a series of fluorenyl-containing tetrasubstituted ethylenes for their novel optical properties and structural features. The dyes show morphology-dependent luminescence. Their emission color can be switched between green and blue by means of mechanical grinding and solvent fuming. The transformation between crystalline and amorphous accounts for the luminescence changing. Through single-crystal and X-ray diffraction (XRD) analysis, the twisted molecular geometries and loose packing motifs in the crystalline samples are believed to be the intrinsic origin of the external-stimuli-induced structural transformation.

Bulk crystal growth and characterization of semi-organic nonlinear optical crystal tri-diethylammonium hexachlorobismuthate (TDCB)

Bulk semi-organic nonlinear optical (NLO) single-crystals of tri-diethylammonium hexachlorobismuthate (TDCB) with sizes up to 22 × 21 × 15 mm3 have been grown from concentrated hydrochloric acid by the slow-cooling method. TDCB crystallizes in the trigonal system, the R3c space group, with a = 14.699(4) A and c = 19.102(5) A. Its morphology has been indexed to reveal the major facets of the crystal to be {110} and {012}. Transmittance spectra of TDCB show an optical transmission in the entire visible region with the cutoff wavelength at 365 nm. The powder second harmonic generation (SHG) measured by using the Kurtz and Perry technique indicates that TDCB is a phase-matchable NLO material with a SHG efficiency of 1.8 times that of KH2PO4 (KDP). Its specific heat and thermal expansion were investigated as a function of temperature, and the relationship between the structure and the thermal properties has been discussed. Furthermore, laser-induced damage threshold measurements show a threshold up to 2.32 GW cm−2. All the results demonstrate that the semi-organic crystal TDCB is promising in NLO applications.

The Role of Weak Interactions in the Mechano-induced Single-Crystal-to-Single-Crystal Phase Transition of 8-Hydroxyquinoline-Based Co-crystals

Mechano-induced single-crystal-to-single-crystal (SCSC) phase transitions in crystalline materials that change their properties have received more and more attention. However, there are still too few examples to study molecular-level mechanisms in the mechano-induced SCSC phase transitions, making the systematic and in-depth understanding very difficult. We report that bis-(8-hydroxyquinolinato) palladium(II)-tetracyanoquinodimethane (PdQ2 -TCNQ) and bis-(8-hydroxyquinolinato) copper(II)-tetracyanoquinodimethane (CuQ2 -TCNQ) show very different mechano-response behaviors during the SCSC phase transition. Phase transition in CuQ2 -TCNQ can be triggered by pricking on the crystal surface, while in PdQ2 -TCNQ it can only be induced by applying pressure uniformly over the whole crystal face. The crystallography data and Hirshfeld surface analysis indicate that the weak intra-layer C-H⋅⋅⋅O, C-H⋅⋅⋅N hydrogen bonds and inter-layer stacking interactions determine the feasibility of the SCSC phase transition by mechanical stimuli. Weaker intra-layer interactions and looser inter-layer stacking make the SCSC phase transition occur much more easily in the CuQ2 -TCNQ.

In Situ Imaging of On-Surface, Solvent-Free Molecular Single-Crystal Growth

The formation of crystalline materials has been studied for more than a century. Recent discoveries about the self-assembly of many inorganic materials, involving aggregation of nanoparticle (NP) precursors or pre-nucleation clusters, challenge the simple assumptions of classical crystallization theory. The situation for organic materials is even more of a terra incognita due to their high complexity. Using in situ high-temperature atomic force microscopy during the solvent-free crystallization of an organic compound [Ni(quinolone-8-thiolate)2], we observe long-range migration of NPs on a silica substrate and their incorporation into larger crystals, suggesting a non-classical pathway in the growth of the molecular crystal.

L-Carnitine inhibits eryptosis induced by uremic serum and the related mechanisms

Abstract Objective: To investigate whether L-carnitine (LC) inhibits eryptosis induced by uremic serum and the related mechanism. Methods: One percent erythrocyte suspension was cultured by three kinds of mediums in vitro, which was included in the control group (Group C, phosphate buffered saline [PBS]), the uremic serum group (Group U, 30% uremic serum + 70% PBS) and the LC group (Group L, 30% uremic serum + 70% PBS + 200 umol/L LC), respectively. Erythrocytes were collected at 24 and 48 h, respectively. Phosphatidylserine (PS) was estimated from Annexin-V-binding and reactive oxygen species (ROS) by flow cytometry, glutathione (GSH) was estimated from Enzyme linked immunosorbent assays (ELISA) by Microplate reader. Results: Eryptosis in Group C increased as the incubating time extended (3.43 ± 0.37 at 24 h, 4.21 ± 0.44 at 48 h). Eryptosis increased in Group U compared with Group C (6.5 1 ± 0.71 at 24 h, p < 0.01; 8.55 ± 0.76 at 48 h, p < 0.01), while decreased in Group L compared with Group U (5.80 ± 0.69 at 24 h, p < 0.05; 7.87 ± 0.76 at 48 h, p < 0.05). Meanwhile, ROS of erythrocytes increased in Group U compared with Group C (33.12 ± 1.61 versus 14.83 ± 2.22 at 24 h, p < 0.01; 42.06 ± 1.81 versus 20.94 ± 1.78 at 48 h, p < 0.01), and GSH decreased in Group U compared with Group C (25.66 ± 0.32 versus 31.27 ± 0.38 at 24 h, p < 0.01; 8.53 ± 0.59 versus 17.29 ± 0.54 at 48 h, p < 0.01). ROS of erythrocytes decreased in Group L compared with Group C (26.29 ± 1.69 at 24 h, p < 0.01; 36.21 ± 2.00 at 48 h, p < 0.01). GSH increased in Group L compared with Group U (27.54 ± 0.60 at 24 h, p < 0.01; 15.18 ± 0.42 at 48 h, p < 0.01). Conclusions: LC inhibits eryptosis induced by uremic serum, which possibly relates to oxidative stress in part.