It remains a challenge to precisely tailor the morphology of polymer monolayers to control charge transport. Herein, the effect of the dissolution temperature (Tdis) is investigated as a powerful strategy for morphology control. Low Tdis values cause extended polymer aggregation in solution and induce larger nanofibrils in a monolayer network with more pronounced π–π stacking. The field‐effect mobility of the corresponding monolayer transistors is significantly enhanced by a factor of four compared to devices obtained from high Tdis with a value approaching 1 cm2 V?1 s?1. Besides that, the solution kinetics reveal a higher growth rate of aggregates at low Tdis, and filtration experiments further confirm that the dependence of the fibril width in monolayers on Tdis is consistent with the aggregate size in solution. The generalizability of the Tdis effect on polymer aggregation is demonstrated using three other conjugated polymer systems. These results open new avenues for the precise control of polymer aggregation for high‐mobility monolayer transistors. 相似文献
DTfBT‐Th3, a new conjugated polymer based on dithienobenzothiadiazole and terthiophene, possesses a bandgap of ≈1.86 eV and a HOMO level of −5.27 eV. Due to strong interchain aggregation, DTfBT‐Th3 can not be well dissolved in chlorobenzene (CB) and o‐dichlorobenzene (DCB) at room temperature (RT), but the polymer can be processed from hot CB and DCB solutions of ≈100 °C. In CB, with a lower solvation ability, a certain polymer chain aggregation can be preserved, even in hot solution. DTfBT‐Th3 displays a field‐effect hole mobility of 0.55 cm2 V−1 s−1 when fabricated from hot CB solution, which is higher than that of the device processed from hot DCB (0.16 cm2 V−1 s−1). In DTfBT‐Th3‐based polymer solar cells, a good power conversion efficiency from 5.37% to 6.67% can be achieved with 150−300 nm thick active layers casted from hot CB solution, while the highest efficiency for hot DCB‐processed solar cells is only 5.07%. The results demonstrate that using a solvent with a lower solvation ability, as a “wet control” process, is beneficial to preserve strong interchain aggregation of a conjugated polymer during solution processing, showing great potential to improve its performances in optoelectronic devices.
The melting temperature, Tm, and the crystalline relaxation temperature, Tαc, of palmitic acid and dipalmitoyl phosphatidylcholine monolayers on the water surface were evaluated by combination of two kinds of measurements: first, the subphase temperature, Tsp, dependence of the monolayer modulus based on the surface pressure-area (π-A) isotherm and second, the Tsp dependence of the electron diffraction, ED patterns of their monolayers. On the basis of their characteristic temperatures of the monolayers, the aggregation structure of the monolayers which were transferred onto a hydrophilic SiO substrate at various surface pressures and Tsps was investigated by means of transmission electron microscopy. The π-A isotherm for the fatty acid monolayer on the pure water surface represented the aggregating process of isolated domains grown right after spreading a solution on the pure water surface. The fatty acid monolayer on the pure water surface was classified into a crystalline monolayer (Tsp < Tm) and an amorphous one (Tsp > Tm). The crystalline monolayer was further classified into two types; crystalline domains were aligned along their crystallographic axes owing to an induced sintering at the interfacial region among monolayer domains by surface compression (Tsp < Tαc), while not for Tsp > Tαc. In the case of the phospholipid monolayer, the monolayer was classified into a compressing crystallized monolayer (Tsp < Tm) and an amorphous one (Tsp > Tm). The compressing crystallized monolayer is a monolayer in which crystallization was gradually induced at plateau region on the π-A isotherm by compression. Electron diffraction studies of arachidic acid monolayers in different dissociated states of hydrophilic groups revealed that formation of the compressing crystallized monolayer was attributed to an electrostatic repulsion among ionic hydrophilic groups. It was concluded that the aggregation structure of monolayers on the water surface was systematically classified into ‘the crystalline monolayer’, ‘the amorphous monolayer’ and ‘the compressing crystallized monolayer’, with respect to thermal and chemical (intermolecular repulsive) factors. 相似文献
The Z-scheme process is a photoinduced electron-transfer pathway in natural oxygenic photosynthesis involving electron transport from photosystem II (PSII) to photosystem I (PSI). Inspired by the interesting Z-scheme process, herein a photocatalytic hydrogen evolution reaction (HER) employing chlorophyll (Chl) derivatives, Chl-1 and Chl-2, on the surface of Ti3C2Tx MXene with two-dimensional accordion-like morphology, forming Chl-1@Chl-2@Ti3C2Tx composite, is demonstrated. Due to the frontier molecular orbital energy alignments of Chl-1 and Chl-2, sublayer Chl-1 is a simulation of PSI, whereas upper layer Chl-2 is equivalent to PSII, and the resultant electron transport can take place from Chl-2 to Chl-1. Under the illumination of visible light (>420 nm), the HER performance of Chl-1@Chl-2@Ti3C2Tx photocatalyst was found to be as high as 143 μmol h−1 gcat−1, which was substantially higher than that of photocatalysts of either Chl-1@Ti3C2Tx (20 μmol h−1 g−1) or Chl-2@Ti3C2Tx (15 μmol h−1 g−1). 相似文献
The following surface-active monomers with methacrylic group at the end of hydrophobic tail: 12-methacryloyloxydodecanoic acid (12-MAODA) and 12-(methacryloyloxydodecanoyl)-glycerophosphatidylcholine 12-MAODPC) were synthesized and investigated. Both monomers are forming monolayers at the liquid/gas interfaces with liquid-expanded and liquid-condensed states at low and high surface pressures, respectively. These monomers have been polymerized in the monolayers just by soft UV-irradiation (254 nm). Dependences of polymerization rate vs. surface pressure for both monomers have maxima (3.33*10−4 s−1 for 12-MAODPC and 4.89*10−4 s−1 for 12-MAODA) at about 8–10 mN/m. The higher polymerization rate of 12-MAODA polymerization as compared to 12-MAODPC is due to the more dense packing of the acid molecules in monolayers as compared to the lipid. Areas per monomer unit in the obtained polymeric monolayers are much smaller than those for the monomer one. The collapse pressures increase after monomer polymerization that evidences the increase of the monolayer stability in case of polymer as compared to monomer. 相似文献
This study presents a new class of conjugated polycyclic molecules that contain seven‐membered rings, detailing their synthesis, crystal structures and semiconductor properties. These molecules have a nearly flat C6‐C7‐C6‐C7‐C6 polycyclic framework with a p‐quinodimethane core. With field‐effect mobilities of up to 0.76 cm2 V−1 s−1 as measured from solution‐processed thin‐film transistors, these molecules are alternatives to the well‐studied pentacene analogues for applications in organic electronic devices. 相似文献
Poly(methylacrylamide) (PMAM) is a thermo-responsive polymer with an upper critical solution temperature (UCST). Its cloud point (Tcp) is around 60 °C, unsuitable for certain biomedical and industrial applications. This study brought up a copolymerization strategy to tune the Tcp of PMAM with hydrophilic comonomers. Surprisingly, with a small portion of hydrophilic monomer doped, the Tcp of the PMAM copolymer can be significantly shifted. For instances, with ≤7 mol% of acrylamide or 1 mol% of oligo(ethylene glycol) methacrylate, the Tcp can be shifted in a wide range from ~69 to ~0 °C. Microdifferential scanning calorimetry demonstrated that the enthalpic effect during the phase transition of the solutions is indistinctive, while fluorescence measurement with pyrene as a probe revealed that the hydrogen-bonding within polymer chains is enhanced by the hydrophobic aggregation of methyl groups. Therefore, the doped hydrophilic monomer could remarkably alter the ordering of water-molecules and the extent for the aggregation of methyl groups, leading to the pronounced shifting in the Tcp of the copolymers. This work would facilitate the application of PMAM as smart polymer materials and guide the inventions of functional materials based on UCST polymers. 相似文献
Rate coefficients for the reactions of OH with n, s, and iso-butanol have been measured over the temperature range 298 to ∼650 K. The rate coefficients display significant curvature over this temperature range and bridge the gap between previous low-temperature measurements with a negative temperature dependence and higher temperature shock tube measurements that have a positive temperature dependence. In combination with literature data, the following parameterizations are recommended: k1,OH + n-butanol(T) = (3.8 ± 10.4) × 10−19T2.48 ± 0.37exp ((840 ± 161)/T) cm3 molecule−1 s−1k2,OH + s-butanol(T) = (3.5 ± 3.0) × 10−20T2.76 ± 0.12exp ((1085 ± 55)/T) cm3 molecule−1 s−1k3,OH + i-butanol(T) = (5.1 ± 5.3) × 10−20T2.72 ± 0.14exp ((1059 ± 66)/T) cm3 molecule−1 s−1k4,OH + t-butanol(T) = (8.8 ± 10.4) × 10−22T3.24 ± 0.15exp ((711 ± 83)/T) cm3 molecule−1 s−1 Comparison of the current data with the higher shock tube measurements suggests that at temperatures of ∼1000 K, the OH yields, primarily from decomposition of β-hydroxyperoxy radicals, are ∼0.3 (n-butanol), ∼0.3 (s-butanol) and ∼0.2 (iso-butanol) with β-hydroxyperoxy decompositions generating OH, and a butene as the main products. The data suggest that decomposition of β-hydroxyperoxy radicals predominantly occurs via OH elimination. 相似文献
A controversy in molecular electronics is the unexplained large spread in values of the tunneling decay coefficient β in tunneling junctions with self‐assembled monolayers of n‐alkanethiolates (SCn). We show control of the β value over the range 0.4–1.0 nC−1 in junctions by changing the topography of the bottom electrodes that support the SAMs. Very low β values (0.4–0.5 nC−1) are obtained for rough surfaces with large areas of exposed grain boundaries, while β=1.0 nC−1 for smooth surfaces with small areas of exposed grain boundaries. 相似文献
The overall rate constants for H-abstraction (kH) from tetrahydrofuran and D-abstraction (kD) from fully deuterated tetrahydrofuran by chlorine atoms in the temperature range of 298-547 K were determined. In both cases, very weak negative temperature dependences of the overall rate constants were observed, described by the expressions: kH = (1.55 ± 0.13) × 10−10 exp(52 ± 28/T) cm3 molecule−1 s−1 and kD = (1.27 ± 0.25) × 10−10exp(55 ± 62/T) cm3 molecule−1 s−1. The experimental results show that the value of the kinetic isotope effect (kH/kD), amounting to 1.21 ± 0.10, is temperature independent at 298-547 K. 相似文献
Mo- and Fe-containing enzymes catalyze the reduction of nitrate and nitrite ions in nature. Inspired by this activity, we study here the nitrate reduction reaction (NO3RR) catalyzed by an Fe-substituted two-dimensional molybdenum carbide of the MXene family, viz., Mo2CTx : Fe (Tx are oxo, hydroxy and fluoro surface termination groups). Mo2CTx : Fe contains isolated Fe sites in Mo positions of the host MXene (Mo2CTx) and features a Faradaic efficiency (FE) and an NH3 yield rate of 41 % and 3.2 μmol h−1 mg−1, respectively, for the reduction of NO3− to NH4+ in acidic media and 70 % and 12.9 μmol h−1 mg−1 in neutral media. Regardless of the media, Mo2CTx : Fe outperforms monometallic Mo2CTx owing to a more facile reductive defunctionalization of Tx groups, as evidenced by in situ X-ray absorption spectroscopy (Mo K-edge). After surface reduction, a Tx vacancy site binds a nitrate ion that subsequently fills the vacancy site with O* via oxygen transfer. Density function theory calculations provide further evidence that Fe sites promote the formation of surface O vacancies, which are identified as active sites and that function in NO3RR in close analogy to the prevailing mechanism of the natural Mo-based nitrate reductase enzymes. 相似文献
The Langmuir–Blodgett method has been used to transfer mixed monolayers of a porphyrin (TMPyP) and a phospholipid (DMPA) from the air|water interface onto optically transparent indium–tin oxide (ITO) electrodes. The surface concentration of porphyrin, Γ, transferred on the ITO surface, has been obtained by integration of the reduction current from the cyclic voltammograms. The experimental Γ values ranged from Γm=5.19×10−11 mol cm−2, and corresponding to a compact monolayer of porphyrin monomers in a plane orientation with respect to the surface, to Γd=8.65×10−11 mol cm−2, and equivalent to the total amount of the porphyrin molecules at the air|water interface under a compression of 35 mN m−1. Prior to the electrochemical experiments, the transmission spectrum was recorded. The surface concentration obtained of the porphyrin is not directly proportional to the transmission of the film, ΔT. This phenomenon is assigned to the dimer formation and, depending on the surface activity of the ITO electrodes, toward porphyrin adsorption. The dimer structure of TMPyP on an intact ITO electrode is altered with respect to that found at the air|water interface. A simple model has been developed to evaluate the contribution of monomer and dimer phases of the porphyrin in the mixed monolayer. Furthermore, spectroscopic measurements with linearly polarized light under oblique incidence have been performed in order to infer the plane orientation of the TMPyP molecules with respect to the ITO surfaces. 相似文献
Complex multicomponent, multispin molecular system, consisting of a septet trinitrene, two quintet dinitrenes, and three triplet mononitrenes, was obtained by the photolysis of 2,4,6-triazido-3-cyano-5-fluoropyridine in solid argon. To identify these paramagnetic products, electron paramagnetic resonance spectroscopy in combination with line-shape spectral simulations and density functional theory calculations was used. The products of the photolysis was found to be triplet 2,4-diazido-3-cyano-5-fluoropyridyl-6-nitrene (DT = 1.000 cm−1, ET = 0), triplet 2,4-diazido-3-cyano-5-fluoropyridyl-2-nitrene (DT = 1.043 cm−1, ET = 0), triplet 2,6-diazido-3-cyano-5-fluoropyridyl-4-nitrene (DT = 1.128 cm−1, ET = 0 cm−1), quintet 4-azido-3-cyano-5-fluoropyridyl-2,6-dinitrene (DQ = 0.211 cm−1, EQ = 0.0532 cm−1), quintet 2-azido-3-cyano-5-fluoropyridyl-4,6-dinitrene (DQ = 0.208 cm−1, EQ = 0.0386 cm−1), and septet 3-cyano-5-fluoropyridyl-2,4,6-trinitrene (DS = −0.1017 cm−1, ES = −0.0042 cm−1) in a 38:4:7:22:14:4 ratio, respectively. 相似文献