Department of Chemistry, Marquette University , P.O. Box 1881, Milwaukee, Wisconsin 53201-1881, United States.
J Am Chem Soc. 2016 Dec 21;138(50):16337-16344. doi: 10.1021/jacs.6b09209. Epub 2016 Dec 7.
Poly-p-phenylene wires are critically important as charge-transfer materials in photovoltaics. A comparative analysis of a series of poly-p-phenylene (PP) wires, capped with isoalkyl (PP), alkoxy (PP), and dialkylamino (PP) groups, shows unexpected evolution of oxidation potentials, i.e., decrease (-260 mV) for PP, while increase for PP (+100 mV) and PP (+350 mV) with increasing number of p-phenylenes. Moreover, redox/optical properties and DFT calculations of PP/PP further show that the symmetric bell-shaped hole distribution distorts and shifts toward one end of the molecule with only 4 p-phenylenes in PP, while shifting of the hole occurs with 6 and 8 p-phenylenes in PP and PP, respectively. Availability of accurate experimental data on highly electron-rich dialkylamino-capped PP together with PP and PP allowed us to demonstrate, using our recently developed Marcus-based multistate model (MSM), that an increase of oxidation potentials in PP arises due to an interplay between the electronic coupling (H) and energy difference between the end-capped groups and bridging phenylenes (Δε). A comparison of the three series of PP with varied Δε further demonstrates that decrease/increase/no change in oxidation energies of PP can be predicted based on the energy gap Δε and coupling H, i.e., decrease if Δε < H (i.e., PP), increase if Δε > H (i.e., PP), and minimal change if Δε ≈ H (i.e., PP). MSM also reproduces the switching of the nature of electronic transition in higher homologues of PP (n ≥ 4). These findings will aid in the development of improved models for charge-transfer dynamics in donor-bridge-acceptor systems.
聚对亚苯基线作为光电中的电荷转移材料至关重要。对一系列聚对亚苯基（PP）线的比较分析，这些线的端基被异烷基（PP）、烷氧基（PP）和二烷基氨基（PP）基团封端，结果显示氧化电势发生了意想不到的变化，即 PP 的氧化电势降低（-260 mV），而 PP 和 PP 的氧化电势增加（分别为+100 mV 和+350 mV），随着 p-亚苯基数量的增加。此外，PP/PP 的氧化还原/光学性质和 DFT 计算进一步表明，对称钟形空穴分布随着 PP 中仅 4 个 p-亚苯基的存在而扭曲和向分子的一端移动，而在 PP 和 PP 中，空穴的移动分别发生在 6 和 8 个 p-亚苯基处。准确的实验数据可用于高度富电子的二烷基氨基封端的 PP 以及 PP 和 PP，这使我们能够使用我们最近开发的基于马库斯的多态模型（MSM）来证明，PP 中氧化电势的增加是由于电子耦合（H）和端基封端基团与桥联亚苯基之间的能量差（Δε）之间的相互作用。对三个系列的 PP 进行比较，进一步证明可以根据能量间隙Δε和耦合 H 来预测 PP 的氧化能的降低/增加/不变，即如果Δε < H（即 PP）则降低，Δε > H（即 PP）则增加，Δε ≈ H（即 PP）则变化最小。MSM 还再现了 PP 更高同系物中电子跃迁性质的转变（n ≥ 4）。这些发现将有助于开发用于供体桥受体系统中电荷转移动力学的改进模型。
