Ahmed Raka, Manna Arun K
Department of Chemistry and Center for Atomic, Molecular and Optical Sciences & Technologies, Indian Institute of Technology Tirupati, Tirupati, AP 517506, India.
Phys Chem Chem Phys. 2021 Jul 14;23(27):14687-14698. doi: 10.1039/d1cp01473k.
Air-stable perylenediimide (PDI) and its derivatives, in particular the cyano-functionalized ones, have attracted great research attention for their potential use in flexible optoelectronics, organic field-effect-transistors (OFETs) as n-type transport materials and also as non-fullerene acceptors in organic photovoltaics (OPVs). Herein we provide a detailed theoretical study on the optical, electrochemical and charge-transport properties (electron and hole mobilities) in a few CN-substituted PDIs with varied number of -CN at different positions (both symmetric and asymmetric di- and tetra-CN derivatives) using density functional theory (DFT) and time-dependent DFT implementing optimally tuned screened range-separated hybrid (OT-SRSH) combining with kinetic rate theory. All cyano-PDIs studied here are energetically stable and form stable π-stacked structures similar to the pristine one, and also act as better electron acceptors. No significant changes in the PDI optical properties are found with the different ways of CN-functionalization, but, this strongly affects the π-stacked geometry, and thereby the electronic coupling, which greatly modulates the PDI intrinsic carrier mobility. Calculated room-temperature electron mobility for the pristine PDI is in excellent agreement with the reported OFET value (∼0.1 cm2 V-1 s-1). Interestingly, relatively large electronic couplings together with small reorganization energies of the symmetrically substituted tetra-CN PDI result in very large charge mobilities (0.4 cm2 V-1 s-1 for electrons and 5.6 cm2 V-1 s-1 for holes) among the systems studied. Therefore, this may serve as a potential ambipolar transport material and hence, naturally calls for experimental demonstration. This detailed and comprehensive study sheds light on the complex interplays between the -CN numbers and the positions for tailored optoelectronic and charge-transport in several functional PDIs, and also shows routes to molecularly design potential n-type materials.
空气稳定的苝二酰亚胺（PDI）及其衍生物，特别是氰基官能化的衍生物，因其在柔性光电子学、作为n型传输材料的有机场效应晶体管（OFET）以及有机光伏（OPV）中的非富勒烯受体等潜在用途而备受研究关注。在此，我们使用密度泛函理论（DFT）和含时DFT，并结合动力学速率理论，采用最优调谐的屏蔽范围分离杂化（OT-SRSH）方法，对一些在不同位置具有不同数量-CN（对称和不对称的二氰基和四氰基衍生物）的CN取代的PDI的光学、电化学和电荷传输性质（电子和空穴迁移率）进行了详细的理论研究。本文研究的所有氰基-PDI在能量上都是稳定的，并且形成与原始PDI类似的稳定π堆积结构，同时也作为更好的电子受体。不同的CN官能化方式对PDI的光学性质没有显著影响，但这强烈影响了π堆积几何结构，进而影响了电子耦合，这极大地调节了PDI的本征载流子迁移率。计算得到的原始PDI在室温下的电子迁移率与报道的OFET值（约0.1 cm² V⁻¹ s⁻¹）非常吻合。有趣的是，在研究的体系中，对称取代的四氰基PDI相对较大的电子耦合以及较小的重组能导致了非常大的电荷迁移率（电子为0.4 cm² V⁻¹ s⁻¹，空穴为5.6 cm² V⁻¹ s⁻¹）。因此，这可能作为一种潜在的双极性传输材料，自然需要实验验证。这项详细而全面的研究揭示了几种功能化PDI中-CN数量和位置之间复杂的相互作用，这些相互作用决定了光电子和电荷传输特性，同时也展示了分子设计潜在n型材料的途径。
