一种基于芴的大环结构的有效降低内重组能的理论研究

A Theoretical Study on the Effective Reduction of Internal Reorganization Energy Based on the Macrocyclic Structure of Fluorene

有机半导体材料在有机发光二极管(OLED)、有机场效应晶体管(OFET)和有机太阳能电池(OSC)等领域应用广泛,但有机半导体材料的迁移率较低,不利于电子传输.本工作基于芴分子设计并计算研究了具有“口”型结构的一类新型网格结构(OF),与普通的大环分子相比,它具有可以横向延伸的几何结构.利用密度泛函理论研究了其分子结构,环张力能和各种电子性质,包括分子轨道、绝热电离势(IPa)、绝热电子亲和势(EAa)、重组能.此外,利用非共价相互作用和Normal Mode(NM)分析方法分别研究了分子内的弱相互作用和每个振动模式对OF重组能的贡献.结果表明OF分子具有非常弱的环张力能(8.20 kJ/mol),比较容易在实验室中合成.通过分子内弱相互作用分析发现,由于cis-OF横梁上的两个芴单元距离较近并且产生了一定的角度,从而产生了π-π相互作用.与Bis-Fl1,Bis-Fl2,Quarter-Fl1和Quarter-Fl2相比,OF分子的IPa降低,EAa提升,证明了格子化效应能提高分子的空穴和电子注入能力.同时,OF具有较低的IPa,是一种非常具有潜力的p型分子材料.另外,当形成口字型芴格时,OF的空穴重组能和电子重组能都有所降低,说明格子化效应是有效降低重组能的一种方式,为未来设计具有优秀电荷传输性质的有机半导体材料提供了一种有效的策略.

Organic semiconductor materials are widely used in organic light-emitting diodes(OLEDs),organic field-effect transistors(OFETs),and organic solar cells(OSCs),but their low mobility is not conducive to electron transport.In this work,a novel class of grid structures based on fluorene(OF)with a“口”structure has been designed and calculated,which has a geometric structure that can extend laterally compared with ordinary macrocyclic molecules.Density functional theory was utilized to study its molecular structure,ring strain energy,and various electronic properties,including molecular orbitals,adiabatic ionization potential,adiabatic electron affinity potentials,and reorganization energies.In addition,the weak interactions within molecules and the contribution of each vibration mode to the reorganization energy of OF were investigated by using non-covalent interaction analysis and Normal Mode(NM)analysis,respectively.The results show that OF has a weak ring strain energy(8.20 kJ/mol)which will be easily synthesized.Through intramolecular weak interaction analysis,it is found that in cis-OF the two fluorene elements on the beam are close and produce a certain angle,theπ-πinteraction is generated.Compared with Bis-Fl1,Bis-Fl2,Quarter-Fl1 and Quarter-Fl2,the energy gap of OF molecules decreases,the highest occupied molecular orbital(HOMO)energy level increases,and the lowest unoccupied molecular orbital(LUMO)energy level decreases,corresponding to adiabatic ionization potential(IPa)and adiabatic electron affinity(EAa),that is,the IPa of OF molecules decreases and EAa increases,which proves that the lattice effect can improve the hole and electron injection ability of molecules.At the same time,OF has a lower IPa which would be a very potential p-type molecular material.Interestingly,the reorganization energy of both OF molecules decreased compared with BF and QF,indicating that the lattice effect is an effective way to reduce the hole and electron reorganization energy which provides a strategy for the design of organic semiconductor materials with excellent charge transport properties.