Ju Mei,†,‡,∥ Nelson L. C. Leung,†,‡,∥ Ryan T. K. Kwok,†,‡ Jacky W. Y. Lam,†,‡ and Ben Zhong Tang*,†,‡,§ †HKUST-Shenzhen Research Institute, Hi-Tech Park, Nanshan, Shenzhen 518057, China ‡Department of Chemistry, HKUST Jockey Club Institute for Advanced Study, Institute of Molecular Functional Materials, Division of Biomedical Engineering, State Key Laboratory of Molecular Neuroscience, Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China Guangdong Innovative Research Team, SCUT-HKUST Joint Research Laboratory, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China

Aggregation-Induced Emission: Together We Shine, United We Soar!

The long-standing popularity of thermoelectric materials has contributed to the creation of various thermoelectric devices and stimulated the development of strategies to improve their thermoelectric performance. In this review, we aim to comprehensively summarize the state-of-the-art strategies for the realization of high-performance thermoelectric materials and devices by establishing the links between synthesis, structural characteristics, properties, underlying chemistry and physics, including structural design (point defects, dislocations, interfaces, inclusions, and pores), multidimensional design (quantum dots/wires, nanoparticles, nanowires, nano- or microbelts, few-layered nanosheets, nano- or microplates, thin films, single crystals, and polycrystalline bulks), and advanced device design (thermoelectric modules, miniature generators and coolers, and flexible thermoelectric generators). The outline of each strategy starts with a concise presentation of their fundamentals and carefully selected examples. In the end, we point out the controversies, challenges, and outlooks toward the future development of thermoelectric materials and devices. Overall, this review will serve to help materials scientists, chemists, and physicists, particularly students and young researchers, in selecting suitable strategies for the improvement of thermoelectrics and potentially other relevant energy conversion technologies.

Advanced Thermoelectric Design: From Materials and Structures to Devices

The possibility to change the molecular assembled structures of organic and organometallic materials through mechanical stimulation is emerging as a general and powerful concept for the design of functional materials. In particular, the photophysical properties such as photoluminescence color, quantum yield, and emission lifetime of organic and organometallic fluorophores can significantly depend on the molecular packing, enabling the development of molecular materials with mechanoresponsive luminescence characteristics. Indeed, an increasing number of studies have shown in recent years that mechanical force can be utilized to change the molecular arrangement, and thereby the optical response, of luminescent molecular assemblies of π-conjugated organic or organometallic molecules. Here, the development of such mechanoresponsive luminescent (MRL) molecular assemblies consisting of organic or organometallic molecules is reviewed and emerging trends in this research field are summarized. After a brief introduction of mechanoresponsive luminescence observed in molecular assemblies, the concept of "luminescent molecular domino" is introduced, before molecular materials that show turn-on/off of photoluminescence in response to mechanical stimulation are reviewed. Mechanically stimulated multicolor changes and water-soluble MRL materials are also highlighted and approaches that combine the concept of MRL molecular assemblies with other materials types are presented in the last part of this progress report.

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Mechanoresponsive Luminescent Molecular Assemblies: An Emerging Class of Materials

Single atoms immobilized on metal-organic frameworks (MOFs) with unique nanostructures have drawn tremendous attention in the application of catalysis but remain a great challenge. Various single noble-metal atoms have now been successfully anchored on the well-defined anchoring sites of the zirconium porphyrin MOF hollow nanotubes, which are probed by aberration-corrected scanning transmission electron microscopy and synchrotron-radiation-based X-ray absorption fine-structure spectroscopy. Owing to the hollow structure and excellent photoelectrochemical performance, the HNTM-Ir/Pt exhibits outstanding catalytic activity in the visible-light photocatalytic H2 evolution via water splitting. The single atom immobilized on MOFs with hollow structures are expected to pave the way to expand the potential applications of MOFs.

Zirconium-Porphyrin-Based Metal-Organic Framework Hollow Nanotubes for Immobilization of Noble-Metal Single Atoms.

Recent achievements on middle and far-infrared second-order nonlinear optical materials

Developing low-cost and high-efficiency photocatalysts for hydrogen production from solar water splitting is intriguing but challenging. In this study, unique one-dimensional (1D) multi-node MoS2/CdS hetero-nanowires (NWs) for efficient visible-light photocatalytic H2 evolution are synthesized via a facile hydrothermal method. Flower-like sheaths are assembled from numerous defect-rich O-incorporated {0001} MoS2 ultrathin nanosheets (NSs), and {1120}-facet surrounded CdS NW stems are grown preferentially along the c-axis. Interestingly, the defects in the MoS2 NSs provide additional active S atoms on the exposed edge sites, and the incorporation of O reduces the energy barrier for H2 evolution and increases the electric conductivity of the MoS2 NSs. Moreover, the recombination of photoinduced charge carriers is significantly inhibited by the heterojunction formed between the MoS2 NSs and CdS NWs. Therefore, in the absence of noble metals as co-catalysts, the 1D MoS2 NS/CdS NW hybrids exhibit an excellent H2-generation rate of 10.85 mmol·g–1·h–1 and a quantum yield of 22.0% at λ = 475 nm, which is far better than those of Pt/CdS NWs, pure MoS2 NSs, and CdS NWs as well as their physical mixtures. Our results contribute to the rational construction of highly reactive nanostructures for various catalytic applications.

Multi-node CdS hetero-nanowires grown with defect-rich oxygen-doped MoS2 ultrathin nanosheets for efficient visible-light photocatalytic H2 evolution

Infrared nonlinear optical (IR-NLO) materials are the key components in solid-state lasers for military and civilian applications. The development of IR-NLO materials remains urgent because the exi...

Mixed-Anion Inorganic Compounds: A Favorable Candidate for Infrared Nonlinear Optical Materials

High-performance infrared (IR) nonlinear optical (NLO) materials with large laser damage thresholds (LDTs) are urgently needed because the current commercially available AgGaS2, AgGaSe2, and ZnGeP2 suffer their very low LDTs which shorten significantly their service lifetimes Here, a novel sulfide, Ba6Zn7Ga2S16 with a very wide band gap of 35 eV, has been discovered This compound crystallizes in the chiral trigonal R3 space group with a novel 3D framework that is constructed by ZnS4 tetrahedra, Zn3GaS10 supertetrahedra (a T2-type), and Zn3GaS10 quadri-tetrahedral clusters via vertex-sharing Such a novel structure exhibits desirable features which suggest a promising NLO material: phase-matchability (PM), good NLO efficiency (about half that of benchmark AgGaS2), and the highest LDT among PM chalcogenides (28 times that of benchmark AgGaS2) In addition, the density functional theory (DFT) calculations confirm its PM behavior and reveal that the second harmonic generation (SHG) origin is mainly ascribe

Ba6Zn7Ga2S16: A Wide Band Gap Sulfide with Phase-Matchable Infrared NLO Properties

Infrared nonlinear optical (IR NLO) materials are the key materials in the modern laser frequency conversion technology that are widely applied in many fields. Yet, the major issue is lacking of high performance materials with large nonlinear susceptibility and high laser damage threshold, which are two correlated and contradictory parameters. Here, the novel dual ion substitution synergy leads to the discovery of Ba4MGa4Se10Cl2 (M = Zn, 1; Cd, 2; Mn, 3; Cu/Ga, 4; Co, 5; and Fe, 6), crystallizing in the tetragonal I4¯. Polycrystalline 1–4 exhibits very strong IR second harmonic generations (SHG). (1: 59×; 2: 52×; 4: 39×; and 3: 30× that of IR benchmark NLO material AgGaS2). Remarkably, the laser-induced damage threshold of 1 is 143.6 MW cm–2, roughly 17 times that of benchmark AgGaS2. These distinguish 1 as a new promising NLO material. In addition, 1, 2, and 4 illustrate the coexistence of NLO and photoluminescence properties. Especially, 3 demonstrate for the first time the coexistence of triple properties (NLO, photoluminescence, and magnetism) in a single crystal structure. The insights of the driving force of the synergetic substitution, SHG origin, and microscopic contributions of the building units open a new route to discovering novel multi-functional NLO materials.

Strong IR NLO Material Ba4MGa4Se10Cl2: Highly Improved Laser Damage Threshold via Dual Ion Substitution Synergy

A series of 2,6-bis(p-dialkylaminostyryl)-9,10-distyrylanthracene (FCn) cruciforms with N-alkyl chains of different lengths have been synthesized, and their aggregation-enhanced fluorescence and piezochromic luminescence (PFC) behaviours are investigated. These 9,10-distyrylanthracene-containing cruciforms exhibit relatively low fluorescence quantum yields (Φ) in THF solution (Φ ≈ 10%) and moderate aggregation-enhanced emission in aqueous media (Φ ≈ 25%), but strong and chain length-dependent solid-state fluorescence emission. Grinding and pressing experiments indicate that they are all effective PFC materials in terms of mechanical stress-induced spectral shifts (ΔλPFC = 23–54 nm), moreover, the longer alkyl-containing FCn shows a larger ΔλPFC. Powder X-ray diffraction and differential scanning calorimetry measurements reveal that the transformation between the crystalline and amorphous states upon external stimuli is responsible for the reversible PFC behaviour. It is found that increasing the N-alkyl length could effectively decrease the cold-crystallization temperature of the ground states to render the PFC states with a tunable heat-recovering temperature, and ground FC10 and FC12 solids can recover spontaneously to their original states at room temperature.

Cruciform 9,10-distyryl-2,6-bis(p-dialkylamino-styryl)anthracene homologues exhibiting alkyl length-tunable piezochromic luminescence and heat-recovery temperature of ground states

Yanyan Li

Papers

Multi-node CdS hetero-nanowires grown with defect-rich oxygen-doped MoS2 ultrathin nanosheets for efficient visible-light photocatalytic H2 evolution

Mixed-Anion Inorganic Compounds: A Favorable Candidate for Infrared Nonlinear Optical Materials

Ba6Zn7Ga2S16: A Wide Band Gap Sulfide with Phase-Matchable Infrared NLO Properties

Strong IR NLO Material Ba4MGa4Se10Cl2: Highly Improved Laser Damage Threshold via Dual Ion Substitution Synergy

Cruciform 9,10-distyryl-2,6-bis(p-dialkylamino-styryl)anthracene homologues exhibiting alkyl length-tunable piezochromic luminescence and heat-recovery temperature of ground states