Unveiling electron transfer in a supramolecular aggregate for adaptive and autonomous photochromic response.

Interactive and responsive materials are dynamic molecular systems that are capable of modulating their behavior and adapting to environment autonomously. Photochromic materials are among the fascinating class of dynamic responsive systems and widely used in molecular switches and optoelectronic devices. However, the phototriggered color changing largely relies on the conformation transformation of the photochromic motif, which significantly limited their usage in organic liquid solutions. Herein, we demonstrate a photochromic organic supramolecular system by using electron-rich N,N-dimethylacetamide (DMA) and electron-deficient naphthalenediimide (NDI) as a donor and acceptor, respectively. In the binary system, the photo-induced electron transfer through lone pair···π interactions pathway leads to dynamic photochromic response not only in the solution but also in the crystalline aggregated state. Furthermore, by incorporating the supramolecules in the polymer matrix, the transparent polymeric film also exhibits rapid photochromic response, which makes it a promisingly interactive and adaptive photochromic material.

Giant nonlinear optical activity in two-dimensional palladium diselenide.

Nonlinear optical effects in layered two-dimensional transition metal chalcogenides have been extensively explored recently because of the promising prospect of the nonlinear optical effects for various optoelectronic applications. However, these materials possess sizable bandgaps ranging from visible to ultraviolet region, so the investigation of narrow-bandgap materials remains deficient. Here, we report our comprehensive study on the nonlinear optical processes in palladium diselenide (PdSe2) that has a near-infrared bandgap. Interestingly, this material exhibits a unique thickness-dependent second harmonic generation feature, which is in contrast to other transition metal chalcogenides. Furthermore, the two-photon absorption coefficients of 1-3 layer PdSe2 (ß ~ 4.16 × 105, 2.58 × 105, and 1.51 × 105 cm GW-1) are larger by two and three orders of magnitude than that of the conventional two-dimensional materials, and giant modulation depths (αs ~ 32%, 27%, and 24%) were obtained in 1-3 layer PdSe2. Such unique nonlinear optical characteristics make PdSe2 a potential candidate for technological innovations in nonlinear optoelectronic devices.

Dynamic Control of High-Range Photoresponsivity in a Graphene Nanoribbon Photodetector.

Graphene has been demonstrated to be a promising material for optoelectronics and photodetection devices because of its ultra-broadband optical absorption and high carrier mobility. However, its integration with optoelectronic systems has been limited by the zero-bandgap and the lack of a gain mechanism. Herein, we demonstrate a novel photodetector based on the graphene nanoribbons (GRNs) with a sizable bandgap. Utilizing trapping charge at the interface between SiO2 and light-doped silicon, an ultrahigh gain of 22,400 has been obtained. Our devices show an enhanced photoresponsivity (~ 800 AW-1) while the response speed is still fast (up to 10 µs). This photoresponsivity is about two orders of magnitude higher compared to that of a previous graphene-based photodetector. The photodetector exhibits a wide-range tunability via source-drain bias and back gate voltage. Our work addresses key challenges for the photodetectors and potentially provides the desired pathway toward practical application of graphene photodetectors that can be externally manipulated by an electric field with fast response speed and high sensitivity.

Observation of double indirect interlayer exciton in WSe2/WS2 heterostructure.

Interlayer excitons (IX) are produced by the spatially separated electron-hole pairs due to the robust Coulomb interactions in van der Waals transition metal dichalcogenide (TMDC) heterostructures (HSS). IX is characterized by a larger binding energy, and its lifetime is orders of magnitude longer than that of the direct excitons, providing a significant platform for the manufacture of long-lived exciton devices and the exploration of exciton quantum gas. However, the studies are restricted to the single interlayer exciton, and the simultaneous capture and study of double IX remain challenging in the WSe2/WS2 HS. Here, we demonstrate the existence of double indirect IX in the WSe2/WS2 HS with the emission centers at 1.4585eV (∼25.9meV wide) and 1.4885 eV (∼14.4 meV wide) at cryogenic temperature. Interestingly, the intensities of the double IX emission peaks are almost equal, and the energy difference between them is in a good agreement with the cleavage value of the WS2 conduction band (CB). Additionally, diverse types of excitons in the individual materials were successfully observed in the PL spectra at 8 K. Such unique double IX features, in combination with excellent exciton identification, open up new opportunities for further investigations for new physical properties of TMDCs and explorations for the technological innovation of exciton devices.

Luminescence Tunable Europium and Samarium Complexes: Reversible On/Off Switching and White-Light Emission.

Single-molecule functional materials with luminescence tunable by external stimuli are of increasing interest due to their application in sensors, display devices, biomarkers, and switches. Herein, new europium and samarium complexes with ligands having triphenylamine (TPA) groups as the redox center and 2,2'-bipyridine (bpy) as the coordinating groups and diketonate (tta) as the second ligand have been constructed. The complexes show white-light emission in selected solvents for proper mixtures of the emission from Ln3+ ions and the ligands. Meanwhile, they exhibit reversible luminescence switching on/off properties by controlling the external potential owing to intramolecular energy transfer from the Ln3+ ions to the electrochemically generated radical cation of TPA•+. Time-dependent density functional theory (TD-DFT) calculations have been performed to study the electronic spectra. The proposed intramolecular energy transfer processes have been verified by density functional theory (DFT) studies.

Direct Observation of the Linear Dichroism Transition in Two-Dimensional Palladium Diselenide.

The linear dichroism (LD) transition within anisotropic photonic materials displays promising prospects for applications in polarization-wavelength-selective detectors, optical switching, and optical communication. In conventional two-dimensional (2D) anisotropic materials, the LD is predominantly uniaxial over a broad spectrum of wavelengths and arises principally from the reduced symmetry of the materials. However, the LD transition behavior in crystalline 2D materials remains elusive. Here, we demonstrate the observation of a unique LD conversion phenomenon at a wavelength of 472 nm in palladium diselenide (PdSe2) using polarization-resolved absorption spectroscopy. This material exhibits prominent anisotropic responses and a high absorption ratio of αy/αx ≈ 1.11 at 364 nm, 1.15 at 532 nm, and 0.84 at 633 nm. We propose that this abnormal LD conversion behavior originates from the forceful localization rules at different parallel energy bands that exist within this material. Furthermore, the robust periodicity of Ag and B1g modes in polarization-resolved Raman spectroscopy is in good agreement with the theoretical structure symmetry analysis. This indicates the strong intrinsic LD effect in the anisotropic nature of PdSe2, which offers a macrolevel determination of crystal orientations. Such unique LD conversion features, in combination with strong LD effects, enable the air-stable PdSe2 to be a potential candidate for technological innovations in multispectral imaging, sensing, and polarization-sensitive and wavelength-controllable photoelectronic applications.

A Breakdown Enhanced AlGaN/GaN Schottky Barrier Diode with the T-Anode Position Deep into the Bottom Buffer Layer.

In this paper, an AlGaN/GaN Schottky barrier diode (SBD) with the T-anode located deep into the bottom buffer layer in combination with field plates (TAI-BBF FPs SBD) is proposed. The electrical characteristics of the proposed structure and the conventional AlGaN/GaN SBD with gated edge termination (GET SBD) were simulated and compared using a Technology Computer Aided Design (TCAD) tool. The results proved that the breakdown voltage (VBK) in the proposed structure was tremendously improved when compared to the GET SBD. This enhancement is attributed to the suppression of the anode tunneling current by the T-anode and the redistribution of the electric field in the anode⁻cathode region induced by the field plates (FPs). Moreover, the T-anode had a negligible effect on the two-dimensional electron gas (2DEG) in the channel layer, so there is no deterioration in the forward characteristics. After being optimized, the proposed structure exhibited a low turn-on voltage (VT) of 0.53 V and a specific on-resistance (RON,sp) of 0.32 mΩ·cm², which was similar to the GET SBD. Meanwhile, the TAI-BBF FP SBD with an anode-cathode spacing of 5 µm achieved a VBK of 1252 V, which was enhanced almost six times compared to the GET SBD with a VBK of 213 V.

Supramolecular aggregation of a redox-active copper-naphthalenediimide network with intrinsic electron conduction.

A sextuple ordered interpenetrated copper-naphthalenediimide network has been constructed by combining the features of porous metal-organic frameworks and π-conjugated supramolecular aggregation. The material exhibits intrinsic semiconductive features with narrow bandgap energy (1.2 eV) and outstanding electron transport. Theoretical calculations combined with experiments indicate that the high electron conduction may originate from π-d coupling and J-aggregation.

Step-Double-Zone-JTE for SiC Devices with Increased Tolerance to JTE Dose and Surface Charges.

In this paper, an edge termination structure, referred to as step-double-zone junction termination extension (Step-DZ-JTE), is proposed. Step-DZ-JTE further improves the distribution of the electric field (EF) by its own step shape. Step-DZ-JTE and other termination structures are investigated for comparison using numerical simulations. Step-DZ-JTE greatly reduces the sensitivity of breakdown voltage (BV) and surface charges (SC). For a 30-µm thick epi-layer, the optimized Step-DZ-JTE shows 90% of the theoretical BV with a wide tolerance of 12.2 × 1012 cm-2 to the JTE dose and 85% of the theoretical BV with an improved tolerance of 3.7 × 1012 cm-2 to the positive SC are obtained. Furthermore, when combined with the field plate technique, the performance of the Step-DZ-JTE is further improved.

Anion-π Interaction-Induced Room-Temperature Phosphorescence of a Polyoxometalate-Based Charge-Transfer Hybrid Material.

Room-temperature phosphorescence (RTP) was realized for the first time in a polyoxometalate-based charge-transfer (CT) hybrid material bearing polyoxometalates (POMs) as electron-donors (D) and rigid naphthalene diimides (NDIs) as electron-acceptors (A), meanwhile, this hybrid material displayed photochromism as well. The significant D-A anion-π interaction induced an additional through-space charge-transfer pathway. The resulting suitable D-A CT states can efficiently bridge the relatively large energy gap between the NDI-localized 1 π-π* and 3 π-π* states and thus trigger the ligand-localized phosphorescence (3 π-π*).

Inflammation-restricted anti-inflammatory activities of a N-acylethanolamine acid amidase (NAAA) inhibitor F215.

N-Acylethanolamine acid amidase (NAAA) is a cysteine enzyme that catalyzes the hydrolysis of palmitoylethanolamide (PEA). Pharmacological blockage of NAAA elevates PEA levels and exerts powerful anti-inflammatory activities. We have recently identified a highly potent NAAA inhibitor F215. Here, we demonstrated that F215 was an unusual inflammation-restricted NAAA inhibitor. In lipopolysaccharides (LPS) induced acute lung injury (ALI) model, F215 markedly accelerated inflammation resolution, promoted clearance of neutrophils infiltration and alveolar repair in the lungs. F215 efficiently inhibited NAAA and protected endogenous PEA from degradation in ALI model, but it cannot readily suppress the NAAA activity in naïve mice. The inflammation-restricted effect of F215 was further confirmed in the alveolar macrophage, F215 only increased PEA levels and exerted anti-inflammatory effects in activated macrophages, but not in unstimulated macrophages. Moreover, we also showed that the pharmacological effects of F215 were restricted to the local inflamed skin elicited by 12-o-tetradecanoylphorbol-13-acetate (TPA), but not the normal tissues. We believe that F215 could be a useful probe to investigate the function of NAAA, as well as a potent anti-inflammatory agent, and its inflammation-restricted feature might offer a new approach to prevent potential side effects of systemic enzyme inhibition.

A novel trigonal propeller-shaped hybrid tri-neodymium-polyoxometalate exhibiting single-molecule magnet behavior.

A trigonal propeller-shaped hybrid polyoxometalate (POM) (NH2Me2)3{[Nd(Mo4O13)(DMF)4]3(BTC)2}·8DMF (1; BTC = 1,3,5-benzenetricarboxylate) has been synthesized and structurally characterized. The planar {Mo4} segment is tailored from the precursor Lindqvist polyoxoanion [Mo6O19]2- firstly, and plays a key role in the reassembly of 1. Furthermore, the magnetic studies reveal that 1 shows single-molecule magnet (SMM) behavior.

Protonation effect on ligands in EuL: a luminescent switcher for fast naked-eye detection of HCl.

A new luminescent coordination polymer, EuH(L)(2)(NO(3))(2) (EuL, HL = 2-(2-pyridin-2-yl)quinoline-4-carboxylic acid), has been solvothermally synthesized, and its framework of uncoordinated pyridyl rings was exploited for the binding and specific sensing of HCl via a protonation effect. The protonation effect changes the energy of the excited state of the ligands, rendering them unable to act as efficient antennae for Eu(3+) characteristic emission. Thus, we have developed a new, fast and convenient sensor for HCl, a gas harmful for the environment.

Two novel POM-based inorganic-organic hybrid compounds: synthesis, structures, magnetic properties, photodegradation and selective absorption of organic dyes.

The hydrothermal reactions of a mixture of (NH4)6Mo7O24·4H2O, Cu(Ac)2·H2O and 3-bpo ligands at different temperatures result in the isolation of two novel inorganic-organic hybrid materials containing different but related isopolymolybdate units, [Cu(3-bpo)(H2O)(Mo4O13)]·3H2O () and [Cu2(3-bpo)2(Mo6O20)] (). The {Mo4O13}n chains in and unprecedented [Mo6O20](4-) isopolyhexamolybdate anions in are linked by octahedral Cu(2+) ions into two-dimensional hybrid layers. Interestingly, 3-bpo ligands in both and are located on either side of these hybrid layers and serve as arched footbridges to link Cu(ii) ions in the layer via pyridyl N-donors, and at the same time connect these hybrid layers into 3D supramolecular frameworks via weak MoNoxadiazole bonds. Another important point for is that water clusters are filled in the 1D channels surrounded by isopolytetramolybdate units. In addition, dye adsorption and photocatalytic properties of and magnetic properties of have been investigated. The results indicated that complex is not only a good heterogeneous photocatalyst in the degradation of methyl orange (MO) and methylene blue (MB), but also has high absorption capacity of MB at room temperature and can selectively capture MB molecules from binary mixtures of MB/MO or MB/RhB. All MB molecules absorbed on can be completely released and photodegraded in the presence of adequate peroxide. The temperature dependence of magnetic susceptibility revealed that complex exhibits antiferromagnetic ordering at about 5 K, and a spin-flop transition was observed at about 5.8 T at 2 K, indicating metamagnetic-like behaviour from antiferromagnetic to ferromagnetic phases.

pH-dependent assembly of two polyoxometalate host-guest structural isomers based on Keggin polyoxoanion templates.

Two interesting polyoxometalate-templated host­guest compounds 1 and 2 with the same chemical formulae of [Ag6(tpt)4(SiW12O40)Cl2]·2H2O have been obtained by hydrothermal reactions of monolacunary Keggin-type K8[α-SiW11O39]·13H2O with CH3COOAg and tpt ligands under different pH conditions. Compounds 1 and 2 are structural isomers. In 1, the novel chair-like tetranuclear [Ag4(µ3-Cl)2]2+ clusters and additional Ag+ ions are linked by tpt ligands to form a 2D double-layered structure featured with two different types of voids in the layer, and the double-layers are stacked into a 3D host supramolecular framework with 1D channels filled with Keggin [SiW12O40]4− polyoxoanions and water molecules as guests. In 2, Ag+ ions are linked by tpt ligands into a 3D framework of 10(3)-ths topology. The most outstanding structural feature of 2 is that upon six-fold interpenetration among 10(3)-ths nets there are still nanosized channels along the a axis to accommodate Keggin polyoxoanions and water molecules as guests. Compound 2 represents the first example of six-fold interpenetrating cationic networks templated with polyoxoanions. In this work, the obvious differences in structure between 1 and 2 show that hydrochloric acid solution conditions, which offer not only H+ to regulate the pH value but also Cl− to coordinate with Ag+ ions, play an important role in the formation of host frameworks templated by Keggin-type polyoxoanions. The photoluminescence properties of 1 and 2 have been investigated in the solid state.

Supramolecular interactions induced hinge-like motion of a metal-organic framework accompanied by anisotropic thermal expansion.

A novel three-dimensional metal-organic framework (MOF), Ag4(tpt)4{δ-[Mo8O26]}·1.5H2O (A) (tpt = 2,4,6-tris(4-pyridyl)-1,3,5-triazine), possesses a ths-type topology with the hinge deformation mode. The single-crystal X-ray diffraction study shows that A and the dehydrated phase Ag4(tpt)4{δ-[Mo8O26]} (B) display distinct anisotropic thermal expansion with expansion in the b direction but contraction in the ac plane. This rare area negative thermal expansion (NTE) behavior is attributed to the hinged structure model and the supramolecular interactions (argentophilic interaction, π-π interaction) that act as the microscopic driving forces. In addition, supramolecular interactions also play a key role in thermochromic behavior of compound A.

Two hybrid polyoxometalate-pillared metal-organic frameworks.

Two polyoxometalate-pillared 3D compounds, {Cu(5)(2-ptz)(6)(H(2)O)(4)(SiW(12)O(40))}·4H(2)O 1 and {Cu(9)(2-ptz)(12)(H(2)O)(6)(PMo(12)O(40))(2)}·H(2)O 2 (2-ptz = 5-(2-pyridyl)tetrazole) have been constructed based on different polyoxometalate anions, and copper-organic coordination polymer sheets by a hydrothermal method. Magnetic investigations reveal that both 1 and 2 exhibit antiferromagnetic coupling between the Cu(II) ions. Structural studies show the compound 1 exhibits a typical pcu-type net with the Schälfli symbol of {4(12)·6(3)}, and that compound 2 is a (3,4,6)-connected framework with novel {4(4)·6(10)·10}{6(3)}(2){6(5)·8} topology which has not been reported to date.

Surface modification of polyoxometalate host-guest supramolecular architectures: from metal-organic pseudorotaxane framework to molecular box.

Precise controlling of the pH value leads to the formation of a new type of metal-organic pseudorotaxane framework and supramolecular box within accommodating POMs guests.

Assembly of a metal-organic framework by sextuple intercatenation of discrete adamantane-like cages.

Metal-organic frameworks form a unique class of multifunctional hybrid materials and have myriad applications, including gas storage and catalysis. Their structure is usually achieved through the infinite coordination of metal ions and multidentate organic ligands by means of strong covalent bonds. Threaded molecules such as catenanes and rotaxanes have largely been restricted to comprising components of two-dimensional interlocking rings or polygons. There are very few examples of the catenation of polyhedral cages. Although it has been postulated that the infinite extended architecture can be obtained from the polycatenation of a discrete cage based on such threading, this has not been documented to date. Here we describe an infinite three-dimensional metal-organic framework composed of catenated polyhedral cages, in which the framework is achieved by mechanical interlocking of all of the vertices of the cages. The three-dimensional polycatenated framework shows twofold self-interpenetration in its crystal packing. The penetration of polycatenanes creates nanosized voids into which the Keggin polyoxometalate anions are perfectly accommodated as counteranions.