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931.
Yihuan Yu Prof. Zhengping Zhang Prof. Liming Dai Prof. Feng Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(22):5652-5657
Breaking the electroneutrality of sp2 carbon lattice is a viable way for nanocarbon material to modulate the charge delocalization and to further alter the electrocatalytic activity. Positive charge spreadsheeting is preferable for catalyzing the oxygen reduction reaction (ORR) and other electrochemical reactions. Analogously to the case of intramolecular charge transfer by heteroatom doping, electrons in the conjugated carbon lattice can be redistributed by the intermolecular charge transfer from the nanocarbon material to the polyelectrolyte. A copolymeric electrolyte, epichlorohydrin-dimethylamine copolymer (EDC) was synthesized. The EDC-modified carbon nanotube (CNT) hybrid was subsequently fabricated by sonication treatment and served as a metal-free carbonaceous electrocatalyst with remarkable catalytic activity and stability. The resultant hybrid presents positive charge spreadsheeting on CNT as a result of the interfacial electron transfer from CNT to EDC. DFT calculations were further carried out to reveal that the enhancement of the wrapped EDC polyelectrolyte originates from the synergetic effect of the quaternary ammonium-hydroxyl covalently bonded structure. The CNT-EDC hybrid not only provides an atomically precise regulation to modulate nanocarbon materials from inactive carbonaceous materials into efficient metal-free catalysts, but it also opens new avenues to develop metal-free catalysts with well-defined and highly active sites. 相似文献
932.
Dr. Sairaman Seetharaman Dr. Nathalie Zink-Lorre Dr. David Gutiérrez-Moreno Prof. Dr. Paul A. Karr Prof. Dr. Fernando Fernández-Lázaro Prof. Dr. Francis D'Souza 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(13):e202104574
Strong push-pull interactions between electron donor, diaminoazobenzene (azo), and an electron acceptor, perylenediimide (PDI), entities in the newly synthesized A−D−A type triads (A=electron acceptor and D=electron donor) and the corresponding A−D dyads are shown to reveal wide-band absorption covering the entire visible spectrum. Electrochemical studies revealed the facile reduction of PDI and relatively easier oxidation of diaminoazobenzene in the dyads and triads. Charge transfer reversal using fluorescence-spectroelectrochemistry wherein the PDI fluorescence recovery upon one-electron oxidation, deterring the charge-transfer interactions, was possible to accomplish. The charge transfer state density difference and the frontier orbitals from the DFT calculations established the electron-deficient PDI to be an electron acceptor and diaminoazobenzene to be an electron donor resulting in energetically closely positioned PDI δ− -Azo δ+ -PDI δ− quadrupolar charge-transfer states in the case of triads and Azo δ+ -PDI δ− dipolar charge-transfer states in the case of dyads. Subsequent femtosecond transient absorption spectral studies unequivocally proved the occurrence of excited-state charge transfer in these dyads and triads in benzonitrile wherein the calculated forward charge transfer rate constants, kf, were limited to instrument response factor, meaning >1012 s−1 revealing the occurrence of ultrafast photo-events. The charge recombination rate constant, kr, was found to depend on the type of donor-acceptor conjugates, that is, it was possible to establish faster kr in the case of triads (∼1011 s−1) compared to dyads (∼1010 s−1). Modulating both ground and excited-state properties of PDI with the help of strong quadrupolar and dipolar charge transfer and witnessing ultrafast charge transfer events in the studied triads and dyads is borne out from the present study. 相似文献
933.
S. Raj Mohan M. P. Joshi C. Shalu C. Ghosh C. Mukharjee L. M. Kukreja 《Journal of Polymer Science.Polymer Physics》2015,53(20):1431-1439
Charge transport properties in thin films of Poly(2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐1,4‐phenylenevinylene) (MDMO PPV) cast using either chloroform (CF), toluene (TOL), or chlorobenzene (CB) as solvent were investigated. Hole mobility (μ) in these thin films measured using time‐of‐flight transient photoconductivity showed an increasing trend with respect to the solvent used in the same order, that is, μCF (2.4 × 10?7 cm2/Vs) < μTOL (6.9 × 10?7 cm2/Vs) < μCB (2.3 × 10?6 cm2/Vs). Observed variations in mobilities were attributed to different morphologies of MDMO PPV chains in thin films cast using the aforesaid solvents. Nature of the interchain interactions and aggregate formation were obtained using photoluminescence (PL), Raman spectroscopy, and AFM studies. Ratio of PL peak intensities of 0–0 and 0–1 transitions, which is a direct measure of interchain interaction, was the highest in CB and lowest in CF. Variation in the relative intensities of out‐of‐plane wagging of vinylene group (~963 cm?1 mode) in Raman spectra suggested different extent of coiling of polymer chains in these thin films. From these observations, it was elicited that aggregate size and interchain interactions are highest in CB and least in CF. AFM‐based topographic images of thin films further supported these variations in the size of aggregates. Variation in the aggregate sizes and interchain interactions explained the corresponding variation in the mobility. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1431–1439 相似文献
934.
Regulation of Charge Delocalization in a Heteronuclear Fe2Ru System by a Stepwise Photochromic Process 下载免费PDF全文
Guang‐Tao Xu Dr. Bin Li Dr. Jin‐Yun Wang Dr. Dao‐Bin Zhang Prof. Zhong‐Ning Chen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(8):3318-3326
Heteronuclear complexes FeCp2?DTE?C?C?Ru(dppe)2Cl ( 1 o ; dppe=1,2‐bis(diphenylphosphino)ethane, Cp=cyclopentadienyl, DTE=dithienylethene) and FeCp2?DTE?C?C?Ru(dppe)2?C?C?DTE?FeCp2 ( 2 oo ), with redox‐active ferrocenyl and ruthenium centers separated by a photochromic DTE moiety, were prepared to achieve photoswitchable charge delocalization and Fe???Ru electronic communication. Upon UV‐light irradiation of 2 oo , the Fe???Ru heterometallic electronic interaction is increasingly facilitated with stepwise photocyclization, 2 oo → 2 co → 2 cc ; this is ascribed to the gradual increase in π‐conjugated systems. The near‐infrared absorptions in mixed‐valence species [ 2 oo ]+/[ 2 co ]+/[ 2 cc ]+ are gradually intensified following the conversion of [ 2 oo ]+→[ 2 co ]+→[ 2 cc ]+, which demonstrates that the extent of charge delocalization shows progressive enhancement with stepwise photocyclization. As revealed by electrochemical, spectroscopic, and theoretical studies, complex 2 exhibits nine switchable states through stepwise photochromic and reversible redox processes. 相似文献
935.
Haiquan Chen Fengna Dai Mengxia Wang Chunhai Chen Guangtao Qian Youhai Yu 《Journal of polymer science. Part A, Polymer chemistry》2021,59(10):833-842
A pair of isomer diamines containing both benzimidazole and benzoxazole and derived homopolyimides were synthesized for the first time. Due to rich rigid and linear benzoazole units, as well as the strong intermolecular interactions from the hydrogen bonding and the charge transfer complexation (CTC), the obtained polyimides (PIs) exhibited outstanding thermal properties, including high thermal weight loss temperature (Td5% = 540–561°C), high glass transition temperature (Tg = 392–421°C), and low coefficient of thermal expansion (CTE = 1.3–20.9 ppm/°C). In addition, the obtained PIs also showed ideal mechanical properties (TS = 189–240 MPa, TM = 4.1–5.0 GPa and EB = 2.9%–4.7%). These potential novel PI films with high Tg and low CTE were expected to be applied to next generation of flexible display substrate material. 相似文献
936.
Dr. Daiki Umeyama Dr. Linn Leppert Bridget A. Connor Dr. Mary Anne Manumpil Prof. Jeffrey B. Neaton Prof. Hemamala I. Karunadasa 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(43):19249-19256
Replacing the Pb−X octahedral building unit of AIPbX3 perovskites (X=halide) with a pair of edge-sharing Pb−X octahedra affords the expanded perovskite analogs: AIIPb2X6. We report seven members of this new family of materials. In 3D hybrid perovskites, orbitals from the organic molecules do not participate in the band edges. In contrast, the more spacious inorganic sublattice of the expanded analogs accommodates larger pyrazinium-based cations with low-lying π* orbitals that form the conduction band, substantially decreasing the band gap of the expanded lattice. The molecular nature of the conduction band allows us to electronically dope the materials by reducing the organic molecules. By synthesizing derivatives with AII=pyridinium and ammonium, we can isolate the contributions of the pyrazinium-based orbitals in the band gap transition of AIIPb2X6. The organic-molecule-based conduction band and the inorganic-ion-based valence band provide an unusual electronic platform with localized states for electrons and more disperse bands for holes upon optical or thermal excitation. 相似文献
937.
Minlang Yang Dr. In Seob Park Yasuhiro Miyashita Katsunori Tanaka Prof. Dr. Takuma Yasuda 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(33):14059-14065
Herein, the universal design of high-efficiency stimuli-responsive luminous materials endowed with mechanochromic luminescence (MCL) and thermally activated delayed fluorescence (TADF) functions is reported. The origin of the unique stimuli-triggered TADF switching for a series of carbazole–isophthalonitrile-based donor–acceptor (D–A) luminogens is demonstrated based on systematic photophysical and X-ray analysis, coupled with theoretical calculations. It was revealed that a tiny alteration of the intramolecular D–A twisting in the excited-state structures governed by the solid morphologies is responsible for this dynamic TADF switching behavior. This concept is applicable to the fabrication of bicolor emissive organic light-emitting diodes using a single TADF emitter. 相似文献
938.
Guigang Zhang Xinchen Wang 《Angewandte Chemie (International ed. in English)》2019,58(44):15580-15582
Photocatalytic overall water splitting by sulfide‐based materials is a great challenge because of the poor resilience of such materials against hole oxidation. In a recent study, Domen and co‐workers developed an innovative strategy to stabilize sulfide‐based photocatalysts by hybridizing S 3p with O 2p orbitals to produce oxysulfides in which S2? is stable. Further surface engineering of the oxysulfides with dual co‐catalysts promoted charge separation and interface transfer, thus reducing the charge build‐up that inhibits photocorrosion. The pH value of the reaction mixture is a critical consideration for achieving efficient stoichiometric H2 and O2 evolution by these oxysulfide photocatalysts. 相似文献
939.
Tengzhou Ma Ban Xuan Dong Jonathan W. Onorato Jens Niklas Oleg Poluektov Christine K. Luscombe Shrayesh N. Patel 《Journal of polymer science. Part A, Polymer chemistry》2021,59(22):2797-2808
Molecular doping of conjugated polymers (CPs) plays a vital role in optimizing organic electronic and energy applications. For the case of organic thermoelectrics, it is commonly believed that doping CPs with a strong dopant could result in higher conductivity (σ) and thus better power factor (PF). Herein, by investigating thermoelectric performance of a polar side-chain bearing CP, poly(3-(methoxyethoxyethoxy)thiophene) (P3MEET), vapor doped with fluorinated-derivative of tetracyanoquinodimethane FnTCNQ (n = 1, 2, 4), we show that using strong dopants can in fact have detrimental effects on the thermoelectric performance of CPs. Despite possessing higher electron affinity, doping P3MEET with F4TCNQ only results in a σ (27.0 S/cm) comparable to samples doped with other two weaker dopants F2TCNQ and F1TCNQ (26.4 and 20.1 S/cm). Interestingly, F4TCNQ-doped samples display a marked reduction in the Seebeck coefficient (α) compared to F1TCNQ- and F2TCNQ-doped samples from 42 to 13 μV/K, leading to an undesirable suppression of the PF. Structural characterizations coupled with Kang-Snyder modeling of the α–σ relation show that the reduction of α in F4TCNQ-doped P3MEET samples originates from the generation of low mobility carrier within P3MEET's amorphous domain. Our results demonstrate that factors such as dopant distribution and doping efficiency within the crystalline and amorphous domains of CPs should play a crucial role in advancing rational design for organic thermoelectrics. 相似文献
940.