苯并二噻吩/苯并噻二唑ADA型光电化合物:氟取代的影响

在其组成的共轭基元上进行氟取代是有机光电材料功能修饰的常见策略之一.在前期苯并二噻吩/苯并噻二唑ADA型小分子光电化合物基础上,在两个苯并噻二唑基元上引入不同个数的氟取代基,考察氟修饰位置和个数对其基本性质、场效应晶体管和光伏性能的影响.研究表明,随着氟原子数目的增加,化合物的溶解性能降低,热稳定性提高,最高占有轨道和最低空轨道能级降低,但光谱吸收范围变化不大.有机场效应晶体管器件测试表明,当苯并噻二唑单氟代且位于外侧位点时,化合物的空穴迁移率有所降低;当苯并噻二唑双氟代时,迁移率得到了明显提高,达到0.27cm~2·V~(-1)·s~(-1).光伏器件研究发现,氟原子的引入提高了器件的开路电压,但活性层形貌变差,最终导致短路电流密度和电池效率下降.     

卤素、 氰基及N原子修饰对四硫富瓦烯衍生物载流子传输性质影响的理论研究

基于密度泛函理论结合跳跃模型和能带理论研究了氟、 氯、 氰基和N原子的引入对四硫富瓦烯(TTF)衍生物载流子传输性质的影响. 计算结果表明, 嵌N修饰会降低分子重组能, 特别是当N原子靠近TTF主体环时作用更明显. 与引入卤素修饰相比, 引入氰基修饰的分子具有更小的电子和空穴重组能及更低的前线分子轨道(FMO)能级. 同时迁移率的计算结果显示, 分子6具有1.15 cm²·V^-1·s^-1的高电子迁移率, 考虑其较低的LUMO能级, 推测其有望成为潜在的优异电子传输材料, 而相似的电子和空穴迁移率使分子2有望成为潜在的双极性传输材料. 同时还考察了S和N原子之间的弱相互作用, 当S或N原子对分子HOMO(或LUMO)有贡献时, 其相应的空穴(或电子)传输能力会有所提高.     

有机场效应材料氟化噻吩并四硫富瓦烯衍生物的电荷传输性质

噻吩并四硫富瓦烯(TTF)衍生物在有机场效应材料方面有较大的应用前景.应用密度泛函理论B3LYP泛函在6-31G(d,p)基组水平上计算了系列氟取代扩展噻吩并四硫富瓦烯衍生物(c2FT、t2FT及4FT)的轨道能级、电离能(IP)、电子亲和势(EA)和重组能(λ).在此基础上,进一步计算二聚体的迁移率,评估了载流子传输能力,并讨论取代位置和堆积方式对电荷传输性质的影响.计算结果表明,氟取代位置对二噻吩并四硫富瓦烯(DT-TTF)衍生物迁移率及电荷传输性质的影响较小,却有效降低了给电子能力.计算结果对设计和合成高效稳定的光电功能材料具有指导意义.     

蒽类衍生物的电荷传输性质

以具有较高迁移率的对称取代类蒽的衍生物{2,6-二[2-(4-戊基苯基)乙烯基]蒽,DPPVAnt;2,6-二-噻吩蒽,DTAnt;2,6-二[2-己基噻吩]蒽,DHTAnt}为研究对象,采用密度泛函理论的B3LYP方法,在6-31G(d)的基组水平上研究了三种蒽类衍生物的分子结构、电子结构、重组能和电荷传输积分,采用Einstein关系式计算了室温下的载流子迁移率,并与蒽的相关计算结果进行了比较.DPPVAnt是较好的空穴传输材料,其空穴迁移率为0.49cm2·V-1·s-1;DHTAnt有利于电子传输,其电子迁移率为0.12cm2·V-1·s-1;而DTAnt是一种较好的双极性材料,其空穴迁移率和电子迁移率分别为0.069和0.060cm2·V-1·s-1.计算得到的迁移率与实验结果处于同一数量级.三种蒽类衍生物的电子重组能与蒽的相近,而空穴重组能均大于蒽的空穴重组能,大小顺序为蒽DPPVAntDTAntDHTAnt.这与计算的迁移率结果不一致,说明分子的堆积结构决定材料的电荷传输性质.     

苯-噻吩低聚物电子结构及载流子传输性质的理论研究

采用密度泛函理论(DFT)的B3LYP/6-31G(d)方法对以低聚噻吩为端基、 苯并二噻吩(TPT)和并三噻吩(TTT)为共轭桥、 炔键为连接臂的20个模型化合物进行了计算研究. 在优化中性与离子态几何构型基础上, 获得了前线轨道能级、 电离能(IPs)、 电子亲和势(EAs)、 空穴/电子重组能(λ_h/λ_e)、 载流子迁移率(μ_h/μ_e)及吸收光谱等信息. 结果表明, 炔键的引入及端基低聚噻吩的增加对LUMO能级的调控作用较为显著, 而共轭桥的类型对HOMO能级影响较大; 合理选择端基、 共轭桥和连接臂等结构单元可对该类材料吸光波段及强度进行有效调节. 一维电荷传输模型结果表明, 所设计的化合物均是潜在的双极性有机半导体材料, 其中2,7-二([2,2':5',2'-三噻吩]-5-基)苯并[1,2-b:6,5-b']二噻吩(A3)和2,7-二(二噻吩并噻吩-2-基乙炔基)苯并[1,2-b:6,5-b']二噻吩(a-3)具有较高的电子迁移率, 值得进一步的实验探索研究.     

端基对二噻吩和苯并噻吩类共轭桥化合物电子结构及载流子传输性能的影响

采用密度泛函理论(DFT, TDDFT) B3LYP/6-31G(d)和PBE0/6-31G(d)方法对苯乙烯/乙炔为端基, 二噻吩(2T)、苯并二噻吩(TPT)和二苯并噻吩(PTP)为共轭桥的12个化合物进行了系统地计算研究. 在分别优化中性态与离子态几何构型的基础上, 获得了前线轨道能级、电离能(IPs)、电子亲合能(EAs)、重组能(λ_h/λ_e)和电子吸收光谱等信息. 结果表明, 苯乙炔基取代苯乙烯基对LUMO能级影响很小, 但HOMO能级明显降低, 能级差?E和激发能E_v增大, 吸收光谱蓝移10～30 nm, 多数苯乙炔基化合物的重组能均有所降低|端基相同共轭桥分别为2T, TPT和PTP时, HOMO能级逐渐降低, LUMO能级逐渐升高, ?E和E_v依次增大, 吸收光谱依次蓝移30～45 nm. 研究结果还表明, TPT共轭桥化合物的重组能较小, 且λ_h与λ_e相近, 有利于载流子传输平衡, 提高传输速率. 本文设计的苯乙炔基苯并二噻吩(DPATPT)有望成为潜在的传输效率高、抗氧化能力强的载流子传输材料.     

空气稳定的氮杂蔻电子传输材料分子设计及三氮杂蔻衍生物迁移率计算

采用密度泛函理论研究氮功能化对蒄类化合物几何构型、电子结构及载流子传输性质的影响. 结果表明, 引入杂N原子可以线性降低前线轨道能级, 增强电子注入能力与空气稳定性, 且邻位掺杂较迫位和均匀掺杂调节效果更为显著. 其中, 十二氮杂蒄（12ac）具有新颖的“碗状”构型和高的电子亲和势（3.45 eV）, 是潜在的空气稳定电子传输材料构筑单元. 理论预测室温下2,6,10-三对甲氧基苯基-3,4,7,8,11,12-六甲氧基三氮杂蒄（3b）晶体的电子迁移率为0.242 cm2/V s, 预计是良好的电子传输材料, 值得进一步器件化研究.     

空气稳定的氮杂蒄电子传输材料分子设计及三氮杂蒄衍生物迁移率计算

采用密度泛函理论研究氮功能化对蒄类化合物几何构型、电子结构及载流子传输性质的影响.结果表明,引入杂N原子可以线性降低前线轨道能级,增强电子注入能力与空气稳定性,且邻位掺杂较迫位和均匀掺杂调节效果更为显著.其中,十二氮杂蒄(12ac)具有新颖的"碗状"构型和高的电子亲和势(3.45 eV),是潜在的空气稳定电子传输材料构筑单元.理论预测室温下2,6,10-三对甲氧基苯基-3,4,7,8,11,12-六甲氧基三氮杂蒄(3b)晶体的电子迁移率为0.242 cm2/V s,预计是良好的电子传输材料,值得进一步器件化研究.     

二萘嵌苯二酰亚胺衍生物的半导体性质

应用密度泛函理论研究了四种二萘嵌苯二酰亚胺(PDI)(N,N'-二萘嵌苯-3,4,9,10-四羧酸二酰亚胺(1), N,N'-二(3-氯苯甲基)二萘嵌苯-3,4,9,10-四羧酸二酰亚胺(2), N,N'-二(3-氟苯甲基)二萘嵌苯-3,4,9,10-四羧酸二酰亚胺(3)和N,N'-二(3,3-二氟苯甲基)二萘嵌苯-3,4,9,10-四羧酸二酰亚胺(4))半导体材料的最高占据轨道和最低未占据轨道能量、离子化能和电子亲和能以及在电荷传导过程中的重组能. 与化合物2-4的最高占据轨道和最低未占据轨道能量变化相同, 在PDI分子外围引入氯苯甲基或氟苯甲基后导致化合物2-4的绝热电子亲和能有不同程度的增加. 应用Marcus电子传导理论, 计算了这四种半导体材料应用于有机场效应晶体管在电子传递过程中的电子耦合和迁移率. 计算结果表明:这四种化合物相对于金属金电极而言具有较小的电子注入势垒, 是优良的n型半导体材料. 计算的这四种半导体材料的电子传输迁移率分别为5.39, 0.59, 0.023和0.17 cm2·V-1·s-1. 通过研究化合物分子在还原过程中几何结构变化和在化合物3晶体中不同类型的电子传递路径, 合理地解释了化合物1-4在有机场效应晶体管电荷迁移过程中具有较高的电子迁移率.     

薁2/6-位芳基取代的模型化合物的设计合成及性质研究

设计合成了薁2/6-位芳基取代的六个模型化合物1～6,化合物1～3和4～6分别为薁2-位和6-位取代的化合物,其取代基顺序均分别为五氟苯、苯和α-噻吩.对化合物的紫外吸收光谱、荧光光谱、电化学以及质子响应等物理化学性质进行了研究,并结合密度泛函理论(DFT)计算研究了2/6-位不同取代芳基对于薁衍生物的基本物理化学性质的影响.吸收光谱研究表明,在薁的2/6-位引入不同取代芳基均可以使其S0→S2跃迁吸收峰红移(Δλ=6～68nm),2/6-位引入给电子的噻吩基团发生明显红移(Δλ=68/48nm),其中2-位引入给电子噻吩基团红移更加明显(Δλ=68nm).荧光光谱研究表明,在薁6-位引入强拉电子的五氟苯,所得化合物4荧光强度最强(φF=0.082);质子化后,同样含有五氟苯基的化合物1-H~+的荧光强度最强((φF=0.359).电化学和DFT理论计算表明,在薁2/6-位引入拉电子的五氟苯基可显著降低分子的最高已占分子轨道(HOMO)和最低空分子轨道(LUMO)能级(1和4的ΔEHOMO/ΔELUMO分别为-0.23/-0.18和-0.20/-0.15 eV).这些研究结果为基于薁的有机功能分子的设计合成及性质研究提供了有效依据.     

吲哚并咔唑类衍生物载流子传输性质的理论研究

以密度泛函理论结合跳跃模型, 重点研究了氯原子和烷基链的引入对吲哚并咔唑类衍生物传输性质的影响. 计算结果表明, 与吲哚并[3,2-b]咔唑(1)相比, 氯原子的引入增大了2,8-二氯吲哚并[3,2-b]咔唑(2)和2,8-二氯-5,11-二己基吲哚并[3,2-b]咔唑(3)的最高占据分子轨道(HOMO)的离域程度, 而对最低未被占据分子轨道(LUMO)则无显著贡献, 但明显降低了二者的能级. 上述结果表明, 对于LUMO, 氯原子体现了吸电子效应, 而对于HOMO, 氯原子体现了共轭效应. 烷基链的引入使化合物3的空穴迁移率明显高于化合物1和2, 这主要归因于化合物3具有更加紧密的分子堆积, 尤其在跳跃路径A中, 具有更大的分子间电子耦合和轨道重叠. 同时能带结构的计算结果进一步证明, 氯原子和烷基链的同时引入大大改善了吲哚并咔唑类衍生物的电荷传输性能.     

THE CORRELATION EFFECT ON THE CHAIN MOTION CONTRIBUTION TO IONIC TRANSPORT IN POLYMER ELECTROLYTES

The ionic transport process in polymer electrolytes (such as polyethylene oxide) wassimulated numerically on a two dimensional square lattice where charge carriers areaccommodated by the lattice sites connected randomly with available bonds to represent theamorphous chain configuration. Following the dynamic bond percolation theory(DBPT),the chainmotion contribution to the ionic conduction was incorporated via periodical renewal of the randombond configuration. To check and extend the prediction made by DBPT employing global abruptbond renewal,spatial correlation of the bond reassignment was introduced to the system by: 1)regional bond renewal and 2) organized bond motion. It is found that the difference between thediffusivities simulated involving regional bond renewal and those of DBPT becomes negligiblewhen the bond renewal rate approaches the carrier hopping rate.     

Electronic structures and long‐range electron transfer through DNA molecules

Quantum chemical calculation on an entire molecule of segments of native DNA was performed in an ab initio scheme with a simulated aqueous solution environment by overlapping dimer approximation and negative factor counting method. The hopping conductivity was worked out by random walk theory and compared with recent experiment. We conclude that electronic transport in native DNA molecules should be caused by hopping among different bases as well as phosphates and sugar rings. Bloch type transport through the delocalized molecular orbitals on the whole molecular system also takes part in the electronic transport, but should be much weaker than hopping. The complementary strand of the double helix could raise the hopping conductivity for more than 2 orders of magnitudes, while the phosphate and sugar ring backbone could increase the hopping conductivity through the base stacks for about 1 order of magnitude. DNA could transport electrons easily through the base stacks of its double helix but not its single strand. Therefore, the dominate factor that influences the electronic transfer through DNA molecules is the π stack itself instead of the backbone. The final conclusion is that DNA can function as a molecular wire in its double helix form with the conditions that it should be doped, the transfer should be a multistep hopping process, and the time period of the transfer should be comparable with that of an elementary chemical reaction. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 78: 112–130, 2000     

Intermolecular charge transfer in model hydrogen-bonded systems—biological implications

The electronic structure of the model hydrogen-bonded systems has been studied at the all-valence level in relation to the charge transfer mechanism. It is concluded that together with the intermolecular proton transfer an electronic charge transport occurs for hydrogen bonds of 2.70–3.00 Å in length, i.e., when the proton motion within the bond is anticipated. For elucidation of transport properties of one-dimensional hydrogen-bonded systems the tunneling–hopping model is preferred instead of the band theory. The importance of the proposed mechanism of the charge transfer for biological processes has been emphasized.     

二邻苯二胺合镍(Ⅱ)载流子传输性能的理论研究

利用密度泛函理论UB3LYP方法, 对二邻苯二胺合镍(Ⅱ)(PHDANI)的基态和离子态几何结构进行全优化, 模拟其双自由基特性. 运用势能面曲线法计算了PHDANI的空穴和电子重组能. 从晶体结构中选出所有可能最近的载流子传输路径, 计算相应的传输积分, 结合Marcus电荷转移理论探讨PHDANI的载流子传输性质. 计算结果表明, 在单重态双自由基特性下, 空穴和电子的迁移率分别达到0.253和0.135 cm²·V^-1·s^-1, 空穴和电子传输迁移率都很高且能达到平衡, 从理论层面上阐明了PHDANI可以作为很好的双极性传输材料.     

Energy Transport along Conjugated Polymer Chains with Extended Radiative Lifetimes: A Theoretical Study

The ability to improve exciton diffusion lengths is a key issue in optimizing many opto‐electronic devices based on conjugated polymers. On the basis of quantum‐chemical calculations, we investigate a strategy consisting of extending the radiative lifetime of energy carriers through incorporation along the polymer backbone of repeating units with forbidden optical transition. The results obtained for poly(p‐phenylenebutadiyne), PPE, and poly(p‐triphenylenebutadiyne), PTPE, show that the larger number of hops performed by the electronic excitations during their lifetime in PTPE is compensated by the smaller hopping length (associated with the reduced conjugation length), so that similar on‐chain diffusion lengths are predicted in both polymers.     

Can the transition from tunneling to hopping in molecular junctions be predicted by theoretical calculation?

The electron transport mechanism changes from tunneling to hopping as molecular length increases. To validate the theoretical simulation after the transition point and clarify influence of electronic structures on the transition, we calculated the conductance of a series of conjugated molecules by density functional theory together with the nonequilibrium Green's function. We found that the highest occupied molecular orbital energy level, transmission spectrum, and the reorganization energy are good indicators for the transition of the electron transport mechanism. The calculated resistances of short junctions (<50 Å, before the transition point) are consistent with the experimental result, following the tunneling mechanism. However, the theoretical predication failed for long molecules, indicating the limitation of the theoretical framework of elastic scattering when the electron transport mechanism changes to hopping. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011     

Two-Dimensional TeB Structures with Anisotropic Carrier Mobility and Tunable Bandgap

Two-dimensional (2D) semiconductors with desirable bandgaps and high carrier mobility have great potential in electronic and optoelectronic applications. In this work, we proposed α-TeB and β-TeB monolayers using density functional theory (DFT) combined with the particle swarm-intelligent global structure search method. The high dynamical and thermal stabilities of two TeB structures indicate high feasibility for experimental synthesis. The electronic structure calculations show that the two structures are indirect bandgap semiconductors with bandgaps of 2.3 and 2.1 eV, respectively. The hole mobility of the β-TeB sheet is up to 6.90 × 10² cm² V⁻¹ s⁻¹. By reconstructing the two structures, we identified two new horizontal and lateral heterostructures, and the lateral heterostructure presents a direct band gap, indicating more probable applications could be further explored for TeB sheets.     

Enhanced hopping conductivity in low band gap donor-acceptor molecular wires Up to 20 nm in length

We have measured the current-voltage characteristics of conjugated oligo-tetrathiafulvalene-pyromelliticdiimide-imine (OTPI) wires ranging in length from 2.5 to 20.2 nm, contacted by Au electrodes. OTPI wires were built from Au substrates using alternating donor (tetrathiafulvalene, TTF) and acceptor (pyromelliticdiimide, PMDI) building blocks linked via aryl imine groups. Metal-molecule-metal junctions consisting of approximately 100 wires in parallel were prepared by contacting the wire films with an Au-coated atomic force microscope tip. The long OTPI wires exhibit a narrow band gap (<1.5 eV) and multiple redox states, which facilitate carrier injection from the Au contacts for hopping transport. We observe the theoretically predicted change in direct current (DC) transport from tunneling to hopping as a function of systematically controlled wire length, as well as strongly enhanced wire conductivity (0.02 S/cm) in the hopping regime. Hopping conduction is confirmed by length-, temperature-, and field-dependent transport measurements. These nanoscale transport measurements illuminate the role of molecular length and bond architecture on molecular conductivity and open opportunities for greater understanding of hopping transport in conjugated polymer films.