Photocatalytic hydrogen production from water offers an abundant, clean fuel source, but it is challenging to produce photocatalysts that use the solar spectrum effectively. Many hydrogen-evolving photocatalysts are active in the ultraviolet range, but ultraviolet light accounts for only 3% of the energy available in the solar spectrum at ground level. Solid-state crystalline photocatalysts have light absorption profiles that are a discrete function of their crystalline phase and that are not always tunable. Here, we prepare a series of amorphous, microporous organic polymers with exquisite synthetic control over the optical gap in the range 1.94-2.95 eV. Specific monomer compositions give polymers that are robust and effective photocatalysts for the evolution of hydrogen from water in the presence of a sacrificial electron donor, without the apparent need for an added metal cocatalyst. Remarkably, unlike other organic systems, the best performing polymer is only photoactive under visible rather than ultraviolet irradiation.
Covalent triazine frameworks (CTFs) are normally synthesized by ionothermal methods.T he harsh synthetic conditions and associated limited structural diversity do not benefit for further development and practical large-scale synthesis of CTFs.Herein we report anew strategy to construct CTFs (CTF-HUSTs) via apolycondensation approach,which allows the synthesis of CTFs under mild conditions from aw ide arrayo fb uilding blocks.I nterestingly,t hese CTFs displayalayered structure.T he CTFs synthesized were also readily scaled up to gram quantities.T he CTFs are potential candidates for separations,p hotocatalysis and for energy storage applications.I np articular,C TF-HUSTs are found to be promising photocatalysts for sacrificial photocatalytic hydrogen evolution with am aximum rate of 2647 mmol h À1 g À1 under visible light. We also applied ap yro-lyzed form of CTF-HUST-4 as an anode material in asodium-ion battery achieving an excellent discharge capacity of 467 mAh g À1. Covalent organic frameworks (COFs) are an emerging class of porous materials,characterized by their ordered structures, high surface areas,and structural diversity. [1] They have shown promise in applications such as gas adsorption, [2] catalysis, [3] and optoelectronics. [4] Av ariety of methods have been reported to prepare COFs,s uch as polycondensation, [1a, 4a] cyclization reactions, [5] or surface mediated methods. [1b, 6] Covalent triazine frameworks (CTFs) are related to COFs and are typically constructed through cyclization reaction of nitrile aromatic building blocks;t hey feature high physico-chemical stability and high nitrogen content. [5, 7] Because of these characteristics,CTFs have found diverse applications in gas adsorption and storage, [5a, 7a,b] catalysis, [7c-e] and energy storage. [7f,g] There are still, however, al imited number of approaches for the synthesis of CTFs. [5a, 7a] Themost common approach is ionothermal synthesis at high temperatures (! 400 8 8C), which also requires alarge amount of ZnCl 2 to serve as both catalyst and reaction medium. [5a] This method can lead to CTFs with ad egree of crystalline order,b ut the high reaction temperatures cause the partial carbonization of the structure and the materials are obtained in the form of black powders.H ence,C TFs prepared by this method lack an electronic band gap and may be unsuitable for photophysical applications.F urthermore,t hese reaction temperatures consume alarge amount of energy and preclude all but the most stable building blocks,thus limiting the scope for scale up and synthetic diversity.I ti s, therefore,i mperative to find new methods for the synthesis of CTFs under milder conditions. Previous research has shown that CTFs could be synthesized at room temperature,a nd catalyzed by strong and corrosive acid such as trifluoromethylsufonic acid. [7a,b] This avoids carbonization, but the method is obviously not suitable to acid-sensitive building blocks,and also the resulting materials did not have layered structures. Here,wedevelop anew strategy involvi...
Conjugated microporous polymers (CMPs) based on the electron-withdrawing 1,3,5-triazine node (TCMPs) were synthesized by palladium-catalyzed Sonogashira-Hagihara cross-coupling. The porosity in these polymers was found to be comparable to the analogous 1,3,5-connected benzene CMP systems that we reported previously, demonstrating that nodes can be substituted in these amorphous materials in a rational manner, much as for certain crystalline porous metal-organic frameworks. The CO 2 adsorption properties of the TCMPs were measured and compared with the corresponding CMPs, and it was found that the TCMP networks adsorbed more CO 2 than CMP analogues with comparable BET surface areas. Network TNCMP-2 showed the highest surface area (995 m 2 g À1 ) and a CO 2 uptake of 1.45 mmol g À1 at 1 bar at 298 K. The band gap in these triazine-based CMPs could also be engineered through copolymerization with other functional monomers.
Recently, great progress has been achieved in the design and preparation of conjugated organic polymer photocatalysts for hydrogen generation. However, it is still challenging to develop an organic polymer photocatalyst with high photoconversion efficiency. Rational structure design of organic polymer photocatalysts holds the key point to realize high photocatalytic performance. Herein, a series of donor–π–acceptor (D–π–A) conjugated organic copolymer photocatalysts is developed using statistical copolymerization by tuning the feed molar ratio of pyrene (donor) to dibenzothiophene‐S,S‐dioxide (acceptor) units. It reveals that the photocatalytic activity of the resulting copolymers is significantly dependent on the molar ratio of donor to acceptor, which efficiently changes the polymer structure and component. When the monomer feed ratio is 25:75, the random copolymer PyBS‐3 of 10 mg with Pt cocatalyst shows a high hydrogen evolution rate of 1.05 mmol h−1 under UV/Vis light irradiation using ascorbic acid as the hole‐scavenger, and an external quantum efficiency of 29.3% at 420 nm, which represents the state‐of‐the‐art of organic polymer photocatalysts. This work demonstrates that statistical copolymerization is an efficient strategy to optimize the polymer structure for improving the photocatalytic activity of conjugated organic polymer catalysts.
Our study shows that by combination of co-solvent and temperature of solvent post treatment method, the highest power factor of 37.05 μW mK−2 is obtained for PEDOT:PSS post-treated with DMSO at 120 °C.
Monodispersed oligomers have been widely developed and used in different optoelectronic areas due to their well-defined molecular structures, high purity, and solution processability. Star-shaped oligomers are especially interesting for OLED application because of their antiaggregation abilities and stable electroluminescence. In addition, star-shaped donor-pi-acceptor conjugated molecules are known to afford good nonlinear optical and two-photon absorption properties due to the intramolecular charge transfer and cooperative enhancement effects. In this context, three generations of highly soluble 1,3,5-triazine based donor-pi-acceptor compounds, TFT1, TFT2, and TFT3, were prepared through a convergent synthetic strategy and their optoelectronic properties were fully studied, which showed distinct correlations with the structures. Closed-aperture and open-aperture Z-scan methods were employed to measure the nonlinear refractive index and two-photon absorption properties of the oligomers, respectively. TFT1 showed a high nonlinear refractive index of 4.14 x 10(-12) esu in THF solution with an excitation wavelength of 800 nm. Also, TFT1 exhibited a large two-photon absorption cross section of 234 GM and a frequency up-converted two-photon excited fluorescence with a lambda(TPEF)(max) value of 527 nm under 800 nm laser irradiation with a pulse duration of 140 fs. OLED devices using the spin-coated films of these oligomers as an active layer showed intensive blue electroluminescence with a maximum luminance of 3093 cd/m(2) at a current efficiency of 1.47 cd/A from TFT1.
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