Electrochromic Smart Window Based on Transition-Metal Phthalocyanine Derivatives.

Phthalocyanines have been widely investigated as electrochromic materials because of their large conjugated structure. However, they have shown limited applicability due to their complex electrochromism mechanism and low solubility in common organic solvents. Replacement of central metal ions in phthalocyanines affects their stability and is responsible for various electrochromic phenomena, such as color change. Herein, the relationship between the electron d-orbital arrangement in the outermost layer of transition metals and the electrochromic stability of phthalocyanine derivatives has been investigated. An enhanced solubility of phthalocyanines in organic solvents was obtained through the introduction of quaternary tert-butyl substitution. Electrochromic devices fabricated with transition-metal phthalocyanine derivatives showed high response speeds and good stability. The fast color-switching feature between blue/green and blue/purple makes it a promising candidate for smart windows and adaptive camouflage applications.

Synthesis, Characterization and Singlet Fission Behaviors of Heteroatom-Doped Polycyclic Aromatic Hydrocarbons with (ß, ß) Connected Furan/Thiophene Ring.

Singlet fission (SF) has been proven to be an effective strategy to overcome the Shockley-Queisser limit of photovoltaics. However, the materials suitable for SF are relatively rare due to the strict requirements for the occurrence of this process. In the present study, we report the first preparation of two heteroatoms (O and S)-doped polycyclic aromatic hydrocarbons (PAHs) molecules with (ß, ß) connected furan/thiophene ring. The optical and physiochemical properties of both compounds are investigated by a variety of spectroscopies, including UV-vis absorption, photoluminescence and cyclic voltammetry. In addition, their ultrafast excited state dynamics are studied by femtosecond transient absorption. Experimental data showed that the singlet fission efficiency was improved by 2 times when replacing oxygen with sulfur atom, which could provide some guidelines in designing singlet fission materials with better efficiency.

Numerical investigation of the blocking effect of a short duct on propeller noise.

Electric vertical and takeoff/landing vehicles for urban aerial mobility have attracted considerable attention in recent years. Some of these vehicles are equipped with ducted propellers to improve power efficiency, but the duct may also affect propeller noise generation and radiation. This work presents thorough numerical investigations to assess the importance of a short duct on propeller noise radiation. An analytical model is employed to predict noise emission from an isolated propeller, and the boundary element method is adopted to account for acoustic scattering effects. Additionally, an efficient data-clustering method is proposed to accelerate the overall noise prediction process. Parametric studies concerning geometries and the propeller's installation location are performed to exploit the duct's feasibility for low-noise vehicle development. Results suggest that the blocking effect can significantly benefit noise control for different rotating speeds, and installing the propeller at the symmetric plane of the duct can achieve the most noise reduction.

Relationship Between Molecular Structure, Single crystal Packing and Self-Assembly Behavior: A Case Based on Pyrene Imide Derivatives.

Development of new n-type one-dimensional (1D) self-assembly nanostructure and a clear understanding of the relationship between molecular structure and self-assembly behavior are important prerequisites for further designing and optimizing organic optoelectronic nanodevice. In this article, a series of n-type organic semiconductor materials based on pyrene imide were successfully synthesized through [4+2] cycloaddition reactions and their preliminary optical and electrochemical properties were studied. The simulated HOMO-LUMO bandgaps via DFT tallied with the experimental data well. The self-assembly of these materials showed needle or fiber-like morphologies, indicating that different conjugation degree or alkyl group had significant influence on their self-assembly behaviors. Furthermore, the single-crystal packing for these molecules were analyzed and it was found out that the changes of conjugated backbone and functional group would affect certain crystal lattice parameter significantly, such as the intermolecular packing distance and crystal size etc, which would further result in different self-assembly morphology.

Achieving Solution-Processed Non-Doped Single-Emitting-Layer White Organic Light-Emitting Diodes through Adjusting Pyrene-Based Polyaromatic Hydrocarbon.

Single-emitting-layer white organic light-emitting diodes (SEL-WOLEDs) have developed rapidly in recent years due to the outstanding advantages of high efficiency, simple device structure, low cost, less phase separation, and stable emission color. Nevertheless, the relatively complicated host-dopant system is usually essential for most previous SEL-WOLEDs and the development of simple non-doped SEL-WOLEDs lags behind. Hence the straightforward synthesis of single-white-emitting molecules for non-doped SEL-WOLEDs still remains a great challengeable task. In this article, we designed and synthesized two new pyrene-based polyaromatic hydrocarbons (PAHs) and used them as emitting layer materials in the OLED devices. When the molecules change from the mono-fused one to bis-fused one, the emitting light changes from greenish to white color. Further study indicated that the bis-fused molecule PyD with more twisted and extended backbone packed in neat Cmca space group in single-crystal system compared with P21 /n for PyS, which may be favorable to form excimers in the solid state and broaden the emission spectrum in the OLEDs. As a result, a solution-processed non-doped single-white-emitting-molecule SEL-WOLED with high performance (e. g., a high color rendering index of 66) is reported. The findings will be beneficial not only to further development of simple WOLEDs, but also to other related organic optoelectronic technology.

Experimental study of airfoil-rotor interaction noise by wavelet beamforming.

A wavelet-based beamforming method is performed in this investigation to analyze moving acoustic sources in the time-frequency domain, which is of scientific significance and practical importance. The particular problem considered here is the interaction noise from an airfoil and the downstream rotor in the presence of a moving flow, which could find realistic applications in next-generation underwater and aviation systems. A realistic experimental setup is prepared with a rotating blade and the airfoil in an anechoic wind tunnel. The results show that the wavelet-based beamforming method is very suitable for unsteady sound source imaging, which would be able to strengthen the time-frequency analysis capability of acoustic imaging tests and, consequently, possibly leads to deepened physical insights of various transient and moving systems in underwater and aerospace systems.

Rational Control of Charge Transfer Excitons Toward High-Contrast Reversible Mechanoresponsive Luminescent Switching.

A practicable strategy to rationally obtain the reversible mechanochromic luminescent (MCL) material with high-contrast ratio (green versus red) has been established. By introducing a volatile third party (small-sized solvent molecules) into the lattice of charge transfer (CT) cocrystal of mixed-stacking 1:1 coronene (Cor.) and napthalenetetracarboxylic diimide (NDI), a noteworthy reconfigurable molecular assembly is ingeniously achieved owing to the loosely packing arrangement as well as weakened intermolecular interactions. Accordingly, the CT excited state, strongly corresponding to the molecular stacking modes, can be intentionally tailored through external stimulus (heating, grinding, or solvent), accompanying distinct changes in photophysical properties. Subsequently, a high-contrast reversible MCL with highly sensitive and good reproducibility is realized and the underlying mechanism is thoroughly revealed.

Two-Dimensional and Emission-Tunable: An Unusual Perovskite Constructed from Lindqvist-Type [Pb6Br19]7- Nanoclusters.

Preparing low-dimensional perovskite materials with novel building units is highly desirable because such materials have already been demonstrated to show unusual physical properties. In this report, we first reported a new and unusual two-dimensional perovskite framework, [B(HIm)4]4Pb13Br38 (1), constructed from novel Lindqvist-type [Pb6Br19]7- nanoclusters. The as-prepared material shows good water resistance and chemical/heat stability. More importantly, 1 has been proven to exhibit temperature/excitation-wavelength-dependent emission. A possible mechanism has been provided.

Thiophene-Fused-Heteroaromatic Diones as Promising NIR Reflectors for Radiative Cooling.

Developing appropriate NIR-reflective materials to combat near-infrared (NIR) heat radiation (700-2500 nm) from sunlight, avoiding energy accumulation and reduce energy consumption, is important and highly desirable. In this research, four thiophene-fused-heteroaromatic diones were used as basic reflectors to investigate the relationship between their intrinsic molecular structures and NIR-reflective properties. The reflectance intensity can be readily tuned by adjusting the length of the appended aliphatic side chains, as well as the strength of the electron-donating groups. A methoxy-substituted thiophene-fused-heteroaromatic dione showed the best performance in reflecting NIR, and it was used as a coating for a model glass house. The comparison of the internal temperature difference relative to a control house was measured and the maximum temperature was 12 °C lower than that in the control house.

Pyrene-Containing Twistarene: Twelve Benzene Rings Fused in a Row.

Success in obtaining higher-order twistarenes with precise structures is very important for fundamentally understanding the relationship between the structures and physical properties/optoelectronic applications. In this research, by using the advantages from a retro-Diels-Alder process (clean reaction) and the cross-conjugated nature of the pyrene unit, a novel dodeca-twistarene was prepared for the first time. Its structure, confirmed by single-crystal XRD analysis, indicates that it possesses a twisted angle (≈30°), and two neighboring molecules in the crystal lattice are perpendicular to each other because of the twisted character and the strong intermolecular CH-π interactions. However, its basic physicochemical properties suggest its instability in air derives from its elevated HOMO energy level, although NICS calculations confirm that the pyrene units contribution poorly to the π conjugation of the overall molecule.

"Doping" pentacene with sp(2)-phosphorus atoms: towards high performance ambipolar semiconductors.

Recent research progress in black phosphorus sheets strongly encourages us to employ pentacene as a parent system to systematically investigate how the "doping" of sp(2)-phosphorus atoms onto the backbone of pentacene influences its optical and charge transport properties. Our theoretical investigations proved that increasing the contribution of the pz atomic orbital of the sp(2)-phosphorus to the frontier molecular orbital of phosphapentacenes could significantly decrease both hole and electron reorganization energies and dramatically red-shift the absorption of pentacene. The record smallest hole and electron reorganization energies of 69.80 and 95.74 meV for heteropentacene derivatives were obtained. These results suggest that phosphapentacenes (or phosphaacenes) could be potential promising candidates to achieve both higher and balanced mobilities in organic field effect transistors and realize a better power conversion efficiency in organic photovoltaics.

Pushing Up Lithium Storage through Nanostructured Polyazaacene Analogues as Anode.

According to the evidence from both theoretical calculations and experimental findings, conjugated ladder polymers containing large π-conjugated structure, a high number of nitrogen heteroatoms, and a multiring aromatic system, could be an ideal organic anode candidate for lithium-ion batteries (LIBs). In this report, we demonstrated that the nanostructured polyazaacene analogue poly(1,6-dihydropyrazino[2,3g]quinoxaline-2,3,8-triyl-7-(2H)-ylidene-7,8-dimethylidene) (PQL) shows high performance as anode materials in LIBs: high capacity (1750 mAh g(-1), 0.05C), good rate performance (303 mAh g(-1), 5C), and excellent cycle life (1000 cycles), especially at high temperature of 50 °C. Our results suggest nanostructured conjugated ladder polymers could be alternative electrode materials for the practical application of LIBs.

Inorganic-organic hybrid nanoprobe for NIR-excited imaging of hydrogen sulfide in cell cultures and inflammation in a mouse model.

Hydrogen sulfide (H2S) is an important gaseous signaling agent mediated by many physiological processes and diseases. In order to explore its role in biological signaling, much effort has been focused on developing organic fluorescent probes to image H2S. However, these downconversion H2S probes are impractical for bio-imaging beyond a certain depth because of the short tissue penetration of UV/visible light (as an excitation source). In most circumstance, these probes are also not suitable for long-term assay due to photo-bleaching. Herein, a new design to detect H2S based on the coumarin-hemicyanine (CHC1)-modified upconversion nanophosphors is reported. This inorganic-organic integrated nanoprobe is demonstrated to display a fast response time with a large ratiometric upconversion luminescence (UCL) enhancement, and extraordinary photo-stability. CHC1-UCNPs not only can be used for ratiometric UCL monitoring of pseudo-enzymatic H2S production in living cells, but can also be used to identify the risk of endotoxic shock through ratiometric UCL imaging of tissue and measurement of endogenous H2S levels in plasma. The first ratiometric UCL H2S nanoprobe reported here may be further developed as the next-generation diagnostic tool for the detection of inflammatory-related diseases.

Design and Synthesis of a Polyketone Building Block with Vinyl Groups-9,10-Diethyl-9,10-ethenoanthracene-2,3,6,7(9H,10H)-tetraone-and a Preliminary Photoelectrical Property Study of Its Azaacene Derivatives.

Polyketone compounds are powerful building blocks to synthesize various organic functional materials. Despite that a great many number of planar and non-planar polyketone building blocks have been developed, one issue is that generally there are only ketone functional groups on the molecular skeleton, which will constrain their transformation and further limit the development of functional materials. In this work, we report the design and synthesis of a building block 9,10-diethyl-9,10-ethenoanthracene-2,3,6,7(9H,10H)-tetraone with additional vinyl functional groups. In addition, its azaacene derivatives were also synthesized, and their preliminary physicochemical properties were studied.

Development of Cyclic Tetrasiloxane Polymer as a High-Performance Dielectric and Hydrophobic Layer for Electrowetting Displays.

Cyclic tetrasiloxane polymer (CTP) has recently garnered interest as a hydrophobic material with unique properties. This study aims to enhance the dielectric constant of CTP films by introducing excess Si-H groups and to explore the impact of synthesis and processing conditions on the resulting properties. The film demonstrates high hydrophobicity, with contact angles of 107° in air and 165° in n-decane, along with a notable dielectric constant of 5.1°. Furthermore, the CTP film displays reversible electrowetting behavior with low contact angle hysteresis (2°) and possesses good transparency (∼99%) and thermal stability. As such, the CTP film has significant potential as a material for the electric wetting of hydrophobic dielectric layers and may serve as a promising alternative in electrowetting applications.

Insights into the Intrinsic Factors Affecting the NIR Reflectance Based on Rylene Diimide Molecules.

A clear understanding of the relationships between molecular structure and NIR reflectance (700-2500 nm) behavior is important and highly desirable for developing appropriate NIR-reflective materials to combat NIR heat radiation from sunlight. In this research, three groups of imide-based compounds have been adopted to investigate the influence of the intrinsic molecular structures on the NIR-reflective properties. It is found out that for the compounds with alkyl groups, the NIR reflectance will increase as the degree of the conjugated backbone increases, especially for the reflectance from 1750 nm to 2500 nm. In addition, despite that the alkyl or amine groups deteriorate the NIR reflectance, the NIR reflectance varies within a certain interval and the isomers with branched alkyl groups show identical or smaller NIR reflectance than those of isomers with linear alkyl groups. For different compounds, crystallinity seems to almost have no relationship with their NIR reflectance.

Recent Progress in High Linearly Fused Polycyclic Conjugated Hydrocarbons (PCHs, n > 6) with Well-Defined Structures.

Although polycyclic conjugated hydrocarbons (PCHs) and their analogues have gained great progress in the fields of organic photoelectronic materials, the in-depth study on present PCHs is still limited to hexacene or below because longer PCHs are insoluble, unstable, and tediously synthesized. Very recently, various strategies including on-surface synthesis are developed to address these issues and many higher novel PCHs are constructed. Therefore, it is necessary to review these advances. Here, the recent synthetic approach, basic physicochemical properties, single-crystal packing behaviors, and potential applications of the linearly fused PCHs (higher than hexacene), including acenes or π-extended acenes with fused six-membered benzenoid rings and other four-membered, five-membered or even seven-membered and eight-membered fused compounds, are summarized.

Polymeric Graphene Bulk Materials with a 3D Cross-Linked Monolithic Graphene Network.

Although many great potential applications are proposed for graphene, till now none are yet realized as a stellar application. The most challenging issue for such practical applications is to figure out how to prepare graphene bulk materials while maintaining the unique two-dimensional (2D) structure and the many excellent properties of graphene sheets. Herein, such polymeric graphene bulk materials containing three-dimensional (3D) cross-linked networks with graphene sheets as the building unit are reviewed. The theoretical research on various proposed structures of graphene bulk materials is summarized first. Then, the synthesis or fabrication of these graphene materials is described, which comprises mainly two approaches: chemical vapor deposition and cross-linking using graphene oxide directly. Finally, some exotic and exciting potential applications of these graphene bulk materials are presented.

A 3D Haloplumbate Framework Constructed From Unprecedented Lindqvist-like Highly Coordinated [Pb6 Br25 ]13- Nanoclusters with Temperature-Dependent Emission.

Searching novel haloplumbate building units to construct three-dimensional (3D) frameworks is very important and highly desirable because such materials would possess new physical properties and potential applications. Here, by employing tetrakis(N-imidazolemethylene)methane(TIMM) as a structure-directing agent, the first 3D haloplumbate framework constructed from unprecedented Lindqvist-like highly coordinated [Pb6 Br25 ]13- nanoclusters has been successfully prepared under hydrothermal condition, where all Pb2+ centres in [Pb6 Br25 ]13- nanoclusters adopt seven-/eight-coordinated configurations. The as-obtained material is a wide-gap semiconductor (≈3.1 eV) and can be stable up to 320 °C. More importantly, this material has been demonstrated to show temperature-dependent emission. Our results could provide a new strategy to explore novel metal-halide open-framework materials.

Thiadizoloquinoxaline-Based N-Heteroacenes as Active Elements for High-Density Data-Storage Device.

A novel thiadiazoloquinoxaline (TQ)-based donor-acceptor (D-A)-type N-heteroacene (Py-1-TQ) has been demonstrated for promising applications in organic multilevel resistive memory devices. Compared with its counterparts (Py-0-TQ and Py-2-TQ), which show flash-type binary memory behaviors, Py-1-TQ exhibits excellent nonvolatile write-once-read-many-times-type ternary memory effects with high ON2/ON1/OFF current ratios (105.8:103.4:1), which can be attributed to the different electron-withdrawing abilities between the pyrazine unit and TQ species that can induce stepwise D-A charge-transfer processes. These results suggest that TQ-based N-heteroacenes can be potentially useful in ultrahigh-density data-storage devices through the rational D-A tuning.