We use quantum mechanical (QM) methods to interpret the charge transport properties of the self-assembled poly-3-hexylthiophene (P3HT) molecules along the intrachain and interchain directions. Our approach is illustrated by a hopping transport model, in which we examine the variation of the electron-coupling strength (transfer integral) with the torsional angle and the intermolecular distance between two adjacent thiophene segments. We also simulate the packed P3HT structures at various values of temperature and regioregularity via the molecular dynamics (MD) simulations. The MD results indicate that with decreasing the molecular regioregularity and/or increasing temperature, the P3HT backbone chains experience a larger distortion of the thiophene rings out of coplanarity, and thus the charge mobility along the main chains is reduced. However, as long as the P3HT molecules remain in the ordered lamellar state due to the presence of the pi-pi interaction, the resultant mobility along the pi-pi interchain direction is still significantly less than that along the intrachain direction. Accordingly, the main charge transfer route within the P3HT ordered domains is along the intrachains instead of the interchains.
We theoretically analyze the charge-transfer behavior of regioregular poly(3-hexylthiophene) (rr-P3HT) by quantum mechanical (QM) and molecular dynamics (MD) methods. In particular, we clarify the effects associated with the respective contribution from the ordered and disordered regions. In the ordered regions, the typical value of the hole mobility along the intrachain route is about 1 cm(2) V(-1) s(-1), which is significantly larger than that along the pi-pi interchain route, approximately 10(-2) cm(2) V(-1) s(-1). Our results indicate that the main charge-transfer route within the P3HT ordered lamellae is along the intrachain direction instead of the interchain direction. Moreover, the calculated hole mobility of 10(-2) cm(2) V(-1) s(-1) along the pi-pi interchain route is consistent with the experimental data measured in the P3HT single fibril. In the disordered regions, we propose a crossing-point/bridging-chain model to describe the charge-transport routes. In this model, the hole mobility can reach the limit of around 10(-2) and 1 cm(2) V(-1) s(-1) when the charge takes the interchain route through the crossing points and the intrachain route along the bridging chains, respectively. As expected, the resultant mobility in the disordered state is strongly affected by the ratio of the amount of crossing points and bridging chains. When considering the presence of both ordered and disordered regions, the average overall charge mobility is mainly dominated by the charge transport in the disordered regions. The fact that some of the experimentally measured hole mobility by varying the molecular weight is limited to a maximum value of 10(-2) cm(2) V(-1) s(-1) is mainly due to the presence of more crossing points instead of the bridging chains in the disordered regions. With increasing the amount of the bridging chains in the disordered regions, one can expect an enhancement of the charge mobility, such as to the experimentally obtained high value of 0.1 cm(2) V(-1) s(-1).
Scientists have made tremendous efforts to gain understanding of the water molecules in proteins via indirect measurements such as molecular dynamic simulation and/or probing the polarity of the local environment. Here we present a tryptophan analogue that exhibits remarkable water catalysed proton-transfer properties. The resulting multiple emissions provide unique fingerprints that can be exploited for direct sensing of a site-specific water environment in a protein without disrupting its native structure. Replacing tryptophan with the newly developed tryptophan analogue we sense different water environments surrounding the five tryptophans in human thromboxane A 2 synthase. This development may lead to future research to probe how water molecules affect the folding, structures and activities of proteins.
The catalytic oxidation of toluene has been investigated using a series of Pt/SBA-15 and Pt/SiO 2 catalysts, and the Pt/SBA-15 catalyst exhibits significantly higher catalytic activity for the oxidation of toluene than the Pt/SiO 2 catalysts. The SBA-15-supported Pt nanoparticles possess the ability to strongly dissociate toluene to benzene, hydrocarbon fragments (CH x ), and H 2 at low temperatures, but the Pt/SiO 2 catalysts are nonreactive toward the decomposition of toluene. The products resulting from the dissociation of toluene were easily oxidized by oxygen, thereby positively affecting the conversion rate of toluene oxidation on Pt/ SBA-15. Temperature-programmed desorption measurements clearly indicate that the dissociation reaction mainly consists of breakage of the C−C bonds between the phenyl and methyl groups. Combined density functional theory (DFT) calculations and DRIFT spectroscopy are carried out to investigate the stretching frequency of CO adsorbed on the defect sites of various Pt clusters, suggesting that the subnanosized Pt particles (icosahedron cluster) and/or Pt single atom may be formed in the structure of SBA-15. Pt sites associated with low coordination and subnanoscale Pt particles and/or single Pt atoms in the SBA-15 support can facilitate toluene adsorption and induce strong dissociation.
Regioregular poly(3-hexylthiophene) (P3HT) is a hole transport polymer material used in organic field-effect transistors (OFETs)and can reach mobilities as high as 0.1 cm 2 V −1 s −1 . Factors that affect the charge mobility and the transport mechanisms of P3HT-based OFET systems are therefore of great importance. We use quantum mechanical methods to interpret the charge mobility and the transport properties of self-assembled P3HT molecules along the intra-chain and inter-chain directions. Our approach is illustrated by a hopping transport model, in which we examine the variation of charge mobility with torsional angle and the intermolecular distance between two adjacent thiophene segments. We also simulate packed P3HT structures via molecular dynamics (MD) simulations. The MD results indicate that the resultant mobility along the π − π inter-chain direction is significantly less than that along the intra-chain direction. Accordingly, the main charge-transfer route within the P3HT ordered domains is an intra-chain rather than an inter-chain one. The calculation result for the inter-chain hole mobility is around 10 −2 cm 2 V −1 s −1 , which is consistent with experimental data from P3HT single fibril.
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