Theoretical comparative studies on transport properties of pentacene,pentathienoacene, and 6,13‐dichloropentacene

Pentacene derivative 6,13‐dichloropentacene (DCP) is one of the latest additions to the family of organic semiconductors with a great potential for use in transistors. We carry out a detailed theoretical calculation for DCP, with systematical comparison to pentacene, pentathienoacene (PTA, the thiophene equivalent of pentacene), to gain insights in the theoretical design of organic transport materials. The charge transport parameters and carrier mobilities are investigated from the first‐principles calculations, based on the widely used Marcus electron transfer theory and quantum nuclear tunneling model, coupled with random walk simulation. Molecular structure and the crystal packing type are essential to understand the differences in their transport behaviors. With the effect of molecule modification, significant one‐dimensional π‐stacks are found within the molecular layer in PTA and DCP crystals. The charge transport along the a‐axis plays a dominant role for the carrier mobilities in the DCP crystal due to the strong transfer integrals within the a‐axis. Pentacene shows a relatively large 3D mobility. This is attributed to the relatively uniform electronic couplings, which thus provides more transport pathways. PTA has a much smaller 3D mobility than pentacene and DCP for the obvious increase of the reorganization energy with the introduction of thiophene. It is found that PTA and DCP exhibit lower HOMO (highest occupied molecular orbital) levels and better environmental stability, indicating the potential applications in organic electronics. © 2015 Wiley Periodicals, Inc.     

介电层修饰并五苯/红荧烯双有源有机薄膜晶体管的制备与性能研究

在Si/SiO₂衬底上使用聚甲基丙烯酸甲酯(PMMA)制备器件介电层的修饰层,改善介电层界面质量并诱导有源层生长,从而提高有源层的结晶程度。通过真空蒸镀法生长并五苯/红荧烯双层结构有源层,制备有机薄膜晶体管(OTFT),并研究器件性能随红荧烯层厚度变化的情况。测试结果表明,修饰后的器件阈值电压为-3.55 V,电流开关比大于10⁵,迁移率达到0.0558 cm²/V·s,亚阈值摆幅为1.95 V/dec,器件总体性能得到改善。     

Electrochemical behavior of MF-4SK/polyaniline composites as investigated by membrane voltammetry

Membrane voltammetry was used to investigate composites consisting of perfluorinated MF-4SK membranes and polyaniline (PANI) and synthesized under various conditions. A theoretical analysis of the influence of transport-structure parameters of the ion-exchange membranes on their selectivity and limiting-current value is carried out. For MF-4SK/PANI composites, the increase in the exchange potential at the overlimiting state is found to be more than 2V compared to the original membrane. An analysis of how various factors influence the parameters of a current-voltage curve shows that the presence of anilinium and Fe³⁺ ions in the electromembrane system has no effect on the value of the potential at the onset of the overlimiting state. A phenomenological model is proposed to account for the increased plateau length at the limiting current through a change in the energetic state of water in the perfluorinated-membrane matrix resulting from the template synthesis of polyaniline.     

Chirality Induction and Amplification in the 2,2,2‐Trifluoroethanol⋅⋅⋅Propylene Oxide Adduct

Chirality induction and amplification in a model system, that is, the 2,2,2‐trifluoroethanol (TFE)???propylene oxide (PO) adduct, were investigated using free‐space and cavity‐based Fourier transform microwave spectroscopy, complemented with high level ab initio calculations. Rotational spectra of four out of eight predicted TFE??PO adducts were assigned, and the remaining four were shown to relax to the geometries of the four observed in a jet expansion. The g+ TFE???S‐PO adduct was found to be favored over that of g? TFE???S‐PO by a factor of 2.8 at 60 K. This difference contrasts the TFE dimer for which an extreme case of chirality synchronization was previously reported. All TFE???PO conformers observed take on the open arrangement, in contrast to 2‐fluoroethanol???PO, which prefers the closed arrangement. Furthermore, perfluorination at CH₃ increases the hydrogen‐bonding energy by about 70 % over its ethanol counterpart.     

固相萃取-超高效液相色谱-串联质谱法同时测定大气降水中9种全氟化合物前体物质

采用固相萃取-超高效液相色谱-电喷雾串联三重四极杆质谱联用技术,建立了大气降水中9种全氟化合物前体物质的高通量检测方法。使用HLB固相萃取柱富集和净化降水样品中的目标化合物,以HSS T_3色谱柱(100mm×2.1 mm,1.7μm)为分析柱,甲醇和水作为流动相进行梯度洗脱。质谱以电喷雾负离子电离,采用多反应监测模式检测。9种目标化合物在0.05~5.00μg/L、0.5~50.0μg/L或5.00~500μg/L浓度范围内线性良好,相关系数为0.992 1~0.999 5,方法的检出限为0.05~7.9 ng/L;高、中、低3个添加水平的回收率为76.0%~106%,相对标准偏差为0.72%~13.7%。实验结果表明,该方法灵敏、准确,且具有检测范围广、分析速度快等特点,是一种适用于大气降水样品中全氟化合物前体物质检测分析的方法。     

Quantum Master Equation Approach to Singlet Fission Dynamics in Pentacene Linear Aggregate Models: Size Dependences of Excitonic Coupling Effects

The singlet fission (SF) dynamics of pentacene linear aggregate models are investigated using the quantum master equation method by focusing on the Frenkel excitonic (FE) coupling effects on the SF rate and double triplet (TT) yield as well as on their aggregate size dependences. It is found that for the dimer model, unrealistically large FE couplings are needed to provide significant effects on the SF dynamics, while for the larger aggregate models a realistic FE coupling causes significant variations in the SF dynamics: as increasing the aggregate size, the SF rate rapidly increases, attains the maximum at 8-mer (~3 times enhancement as compared to the non-FE-coupling case) and then decreases, approaching a stationary value after 12-mer, although the stationary TT yield at 20-mer remains slightly smaller than that in the non-FE-coupling case. These features are explained based on the relative relaxation factors between the adiabatic exciton states. The present results contribute to constructing the design guidelines for highly efficient SF aggregates. © 2018 Wiley Periodicals, Inc.     

Delayed phase separation in growth of organic semiconductor blends with limited intermixing

Binary mixed thin films of picene (C₂₂H₁₄, PIC) and pentacene (C₂₂H₁₄, PEN) consist of crystallites with a statistical occupation of the lattice sites by either PEN or PIC and unit cell parameters continuously changing with the mixing ratio. For high PIC ratios a PIC phase forms which corresponds to a limited intermixing of the two compounds. The growth behavior of these mixtures is investigated in situ and in real‐time using grazing incidence X‐ray diffraction. We observe a delayed phase separation in PIC‐rich blends, i.e. complete intermixing in the monolayer range and the nucleation of a pure PIC‐phase in addition to the intermixed phase starting from the second monolayer.

Growth scenario of picene‐rich pentacene‐picene blends.     

Study on solid structure of pentacene thin films using Raman imaging

We present a 532‐nm excited Raman imaging study of pentacene thin films (thickness, 2, 5, 10, 20, 50, 100, and 150 nm) prepared on an SiO₂ surface. The structure of the pentacene films has been investigated by images and histograms of the ratio (R) of intensity of the 1596‐cm⁻¹ band (b_3g) to that of the 1533‐cm⁻¹ band (a_g), which can be used as a marker of solid‐state phases: 1.54‐nm and 1.44‐nm phases. The Raman images showed that island‐like 1.44‐nm phase domains are grown on the 1.54‐nm phase layer from 50 nm, and all the surface of the 1.54‐nm phase layer is covered with the 1.44‐nm phase layer from 100 nm. The structural disorders have been discussed on the basis of the full width at half maximum of a band in the histogram of the R values for each film. Copyright © 2012 John Wiley & Sons, Ltd.