Coordination Compound Guided a Novel Composite Film with Zn2V2O7 Nanoflake and VO2@Zn2V2O7 Nanoparticle for Enhanced Thermochromism Smart Window.

Thermochromic vanadium dioxide (VO2) can intelligently modulate the transmittance of indoor solar radiation to reduce the energy consumption of air conditioning in buildings. Nevertheless, it remains a great challenge to simultaneously improve the luminous transmittance (Tlum) and solar modulation ability (ΔTsol) of VO2. In this study, a novel approach is employed utilizing a coordination compound to finely tune the growth of a VO2 based composite film, yielding a hierarchical film comprising Zn2V2O7 nanoflakes and VO2@Zn2V2O7 core-shell nanoparticles. Remarkably, the resulting composite films showcase exceptional optical performance, achieving a Tlum of up to 73.0% and ΔTsol of 15.7%. These outcomes are attributed to the antireflection properties inherent in the nanoflake structure and the localized surface plasmon resonance of well-dispersed VO2 nanoparticles. In addition, the Zn2V2O7-VO2 film demonstrates remarkable environmental durability, retaining 90% of its initial ΔTsol even after undergoing aging at 100 °C under 50% relative humidity for a substantial period of 30 days - a durability equivalent to ≈20 years under ambient conditions. This work not only achieves a harmonious balance between Tlum and ΔTsol but also introduces a promising avenue for the design of distinctive composite nanostructures.

Main group metal elements enhance electrochemical nitrogen reduction reaction of vanadium-based single atom catalysts through d-p orbital hybridization.

Developing active sites with flexibility and diversity is crucial for single atom catalysts (SACs) towards sustainable nitrogen fixation at ambient conditions. Herein, the effects of doping main group metal elements (MGM) on the stability, catalytic activity, and selectivity of vanadium-based SACs is systematically investigated based on density functional theory calculations. It is found that the catalytic activity of V site can be significantly enhanced by the synergistic effect between MGM and vanadium atoms. More importantly, a volcano curve between the catalytic activity and the adsorption free energy of NNH* can be established, in which V-Pb dimer embedded on N-coordinated graphene (VPb-NG) exhibits optimal NRR activity due to its location at the top of volcano. Further analysis of electronic structures reveals that the unoccupancy ratio (eg/t2g) of V site is dramatically increased by the strong d-p orbital hybridization between V and Pb atoms, subsequently, N2 is activated to a larger extent. These interesting findings may provide a new path for designing active sites in SACs with excellent performance.

Negative Poisson's ratio of sulfides dominated by strong intralayer electron repulsion.

Geometrical variations in a particular structure or other mechanical factors are often cited as the cause of a negative Poisson's ratio (NPR). These factors are independent of the electronic properties of the materials. This work investigates a class of two-dimensional (2D) sulfides with the chemical formula MX2 (M = Ti, Cr, Mn, Fe, Co, X = S) using first-principles calculations. Among them, monolayered TiS2, CrS2, and MnS2 were found to exhibit a structure-independent NPR. The strong strain response of intra-layer interactions is responsible for this unique phenomenon. This can be traced to the lone pair of electrons of the S atoms and the weak electronegativity of the central atoms in multi-orbital hybridization. Our study provides valuable insights and useful guidelines for designing innovative NPR materials.

One stimulus-induced two-step photophysical response with high contrast and tunable switching time for dynamic displaying.

One stimulus-induced two-step photophysical response, especially with tunable switching time, is a great challenge for organic chromophores. Herein, a polymorphic material 2,7-DCF could undergo in situ two sequential dual-channel responses upon dichloromethane fuming. Both the appearance color and the fluorescence change from red to yellow to deep red with high contrast. The first step corresponds to a fast amorphous-to-crystalline transformation, while the second is a slow solid-state cocrystallization process. Based on single crystal structures and theoretical calculations, such distinct color changes are mainly attributed to conformation twisting and the electron coupling with incorporated solvent molecule through C-H⋅⋅⋅O interaction. Importantly, the second slow photophysical response could be drastically sped up by seeding strategy, or be totally inhibited. Such characteristics pave a way for the potential applications in dynamic anti-counterfeiting and data encryption. Based on the two-step transformation, polymorph 2,7-DCF-a could achieve a successive four-level response to external stimuli. In contrast, polymorph 2,7-DCF-d exhibits a stepwise hypsochromic fluorescence shift over 100 nm. This study would significantly promote the development of stimuli-sensitive systems from "one stimulus, one-step response" to "one stimulus, two or multi-step response".

Multistimuli-Responsive Squaraine Dyad Exhibiting Concentration-Controlled Vapochromic Luminescence.

Stimuli-responsive organic materials with controllable luminescence are of enormous importance because of their potential applications in sensing, data security, and display devices. In this study, a multistimuli-responsive squaraine dyad (SQ-d) composed of two rigid squaraine moieties and a flexible ethylene linker was rationally designed and synthesized. SQ-d exhibits polymorphic luminescence, which can be reversibly switched by various external stimuli, including solvent vapor exposure, heat, and shear force. Unexpectedly, the weakly luminescent phase (O1) of SQ-d exhibits concentration-controlled vapochromic behavior. Film O1 can convert to a highly green-emissive phase (G1) under a low concentration of CHCl3 vapor and convert to a highly yellow-emissive phase (Y) under a high concentration of CHCl3 vapor; these originate from two distinct crystallization-induced emission enhancement processes. To the best of our knowledge, this is the first investigation of the effect of vapor concentration on the phase transitions of organic vapochromic luminophores. By analyzing the single-crystal structures and photophysical properties of SQ-d, we concluded that the green and yellow emissions probably originated from a zigzag stacking mode and an H-type π-π stacking mode, respectively. Finally, two prototypes based on SQ-d for applications in information encryption and vapor sensing were successfully demonstrated.

Crystallization-Induced Reversal from Dark to Bright Excited States for Construction of Solid-Emission-Tunable Squaraines.

Squaraines (SQs) with tunable emission in the solid state is of great importance for various demands; however a remaining challenge is emission quenching upon aggregation. Herein, a unique SQ, named as CIEE-SQ, is designed to exhibit strong emission in crystal, undergoing crystallization-induced reverse from dark 1 (n+σ,π*) to bright 1 (π,π*) excited states. Such an excited state of CIEE-SQ can be subtly tuned by molecular conformation changes during the unexpected temperature-triggered single-crystal to single-crystal (SCSC) reversible transformation. Furthermore, co-crystallization between CIEE-SQ and chloroform largely stabilize the 1 (π,π*) state, enhancing the transition dipole moment and decreasing the reorganization energy to boost the fluorescence, which is promising in data encryption and decryption.

Halogenated Tetraazapentacenes with Electron Mobility as High as 27.8 cm2 V-1 s-1 in Solution-Processed n-Channel Organic Thin-Film Transistors.

Molecular engineering of tetraazapentacene with different numbers of fluorine and chlorine substituents fine-tunes the frontier molecular orbitals, molecular vibrations, and π-π stacking for n-type organic semiconductors. Among the six halogenated tetraazapentacenes studied herein, the tetrachloro derivative (4Cl-TAP) in solution-processed thin-film transistors exhibits electron mobility of 14.9 ± 4.9 cm2 V-1 s-1 with a maximum value of 27.8 cm2 V-1 s-1 , which sets a new record for n-channel organic field-effect transistors. Computational studies on the basis of crystal structures shed light on the structure-property relationships for organic semiconductors. First, chlorine substituents slightly decrease the reorganization energy of the tetraazapentacene whereas fluorine substituents increase the reorganization energy as a result of fine-tuning molecular vibrations. Second, the electron transfer integral is very sensitive to subtle changes in the 2D π-stacking with brickwork arrangement. The unprecedentedly high electron mobility of 4Cl-TAP is attributed to the reduced reorganization energy and enhanced electron transfer integral as a result of modification of tetraazapentacene with four chlorine substituents.

Engineering Thin Films of a Tetrabenzoporphyrin toward Efficient Charge-Carrier Transport: Selective Formation of a Brickwork Motif.

Tetrabenzoporphyrin (BP) is a p-type organic semiconductor characterized by the large, rigid π-framework, excellent stability, and good photoabsorption capability. These characteristics make BP and its derivatives prominent active-layer components in organic electronic and optoelectronic devices. However, the control of the solid-state arrangement of BP frameworks, especially in solution-processed thin films, has not been intensively explored, and charge-carrier mobilities observed in BP-based materials have stayed relatively low as compared to those in the best organic molecular semiconductors. This work concentrates on engineering the solid-state packing of a BP derivative, 5,15-bis(triisopropylsilyl)ethynyltetrabenzoporphyrin (TIPS-BP), toward achieving efficient charge-carrier transport in its solution-processed thin films. The effort leads to the selective formation of a brickwork packing that has two dimensionally extended π-staking. The maximum field-effect hole mobility in the resulting films reaches 1.1 cm2 V-1 s-1, which is approximately 14 times higher than the record value for pristine free-base BP (0.070 cm2 V-1 s-1). This achievement is enabled mainly through the optimization of three factors; namely, deposition process, cast solvent, and self-assembled monolayer that constitutes the dielectric surface. On the other hand, polarized-light microscopy and grazing-incident wide-angle X-ray diffraction analyses show that there remains some room for improvement in the in-plane homogeneity of molecular alignment, suggesting even higher charge-carrier mobilities can be obtained upon further optimization. These results will provide a useful basis for the polymorph engineering and morphology optimization in solution-processed organic molecular semiconductors.

Extension of N-Heteroacenes through a Four-Membered Ring.

The synthesis of novel π-extended N-heteroacenes, which have a large tetraazaacene subunit and a quinoxaline subunit connected through a four-membered ring, is reported. They were studied with experimental and computational methods in comparison to the corresponding tetraazaacenes. As found from the DFT calculation, the four-membered ring is a better linker than a five-membered ring or a C-C single bond to extend N-heteroacenes for a new design of n-type semiconductors in terms of the spatial delocalization and energy level of LUMO as well as the reorganization energy. In solution-processed thin film transistors, the π-extended N-heteroacenes are found to function as n-type semiconductors with field effect mobility of up to 0.02 cm(2) V(-1) s(-1) under ambient conditions.

Molecular packing and n-channel thin film transistors of chlorinated cyclobuta[1,2-b:3,4-b']diquinoxalines.

Novel chlorinated cyclobuta[1,2-b:3,4-b']diquinoxalines were synthesized and investigated in the solid state. It is found that their molecular packing can be tuned by varying the number and position of chlorine substituents, and 2,8-dichloro-cyclobuta[1,2-b:3,4-b']diquinoxaline either in pure form or as a mixture with its regioisomer functions as n-type semiconductors in organic thin film transistors with a field effect mobility of up to 0.42 cm(2) V(-1) s(-1) and 0.20 cm(2) V(-1) s(-1), respectively.

Synthesis, solution-processed thin film transistors and solid solutions of silylethynylated diazatetracenes.

Silylethynylated diazatetracenes were synthesized in a more efficient way and applied as n-type semiconductors in solution-processed thin film transistors with an electron mobility of 0.65 cm(2) V(-1) s(-1). Co-crystallization of these diazatetracenes with silylethynylated tetracene resulted in solid solutions, which exhibited interesting electrical and optical properties.

Regiospecific N-heteroarylation of amidines for full-color-tunable boron difluoride dyes with mechanochromic luminescence.

Colors to dye for: Palladium-catalyzed regiospecific N-heteroarylations of amidines with 2-halo-N-heteroarenes leads to a structurally diverse library of BF2 /amidine-based complexes. These dyes not only present full-visible-color solid-state emissions with large Stokes shifts and high fluorescence quantum yields, but also exhibit a full-color-tunable mechanofluorochromic nature.

Facile access to extremely efficient energy-transfer pairs via an unexpected reaction of squaraines with ketones.

We have discovered that squaraine NCSQ easily react with ketones in the presence of ammonium acetate to form a novel type of squaraine CCSQ. It is interesting to find that NCSQs exhibit unusual solid-state fluorescence, whereas CCSQs only exhibit fluorescence in solution. The quantum yield of solid NCSQ-g is measured to be 0.36, which is the highest among solid squaraines found so far. The large spectral overlap between the emission of NCSQs and the absorption of CCSQs, and the structural similarity of these molecules make them excellent energy-transfer (ET) pairs, as exemplified by the ET pair of CCSQ-1/NCSQ-g. When a very small amount (0.05 mol%) of CCSQ-g is doped into NCSQ-g, the ET efficiency reaches up to 96%. The Stern-Volmer quenching constant K(SV) is calculated to be 65 800, indicating that CCSQ-1/NCSQ-g forms an extremely efficient ET pair. This study provides a novel skeleton and a facile route to efficient ET pairs.

Ultrasound-induced switching of sheetlike coordination polymer microparticles to nanofibers capable of gelating solvents.

We herein demonstrate a new gelation mechanism based on a readily available coordination polymer {Zn(bibp)(2)(OSO(2)CF(3))(2)}(n), in which ultrasound changes the morphology of the material from sheetlike microparticles into nanofibers, resulting in the immobilization of organic solvents.

Helical nonracemic tubular coordination polymer gelators from simple achiral molecules.

A novel class of helical nonracemic tubular coordination polymers, which can immobilize a wide range of solvents at very low concentrations, have been synthesized for the first time in the absence of chiral influences and appended groups.