Theoretical Investigation And Molecular Design Of Organic Optoelectronic Materials

In this paper, Density Functional Theory (DFT) and Time-dependent DFT were adopted to investigate the photoelectric properties of a series of aromatic compounds. After calculation of their monomer, oligomer and stacking structure, we designed some new compounds and discussed their potential application to be the donor material of organic solar cell, the host material of organic light emitting diode and organic transport material with high mobility, respectively.In Chapter1, we gave a brief account about the research status of organic optoelectronic materials. Secondly, the working principle and research status of organic solar cell and doped phosphorescent organic light-emitting diodes were presented. Furthermore, the importance of our work was pointed out.In Chapter2, a thorough introduction to the calculational methods applied in this paper Density Functional Theory (DFT) and Time-dependent DFT (TDDFT) were included. In addition, we also introduced some other theoretical methods and measures, including atoms in molecular (AIM) theory, nucleus-independent chemical shifts (NICS) and nature bond orbital (NBO).In Chapter3, based on the structure and properties of PFDTBT Poly{[2,7-(9,9’-dihexylfluorene)]-alt-[4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole]}, three new kinds of donor materials: poly{[2,7-(9,9’-dihexylfluorene)]-alt-[4,7-di(thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-d]py ridazine]}(PFDTTDP), poly{[2,7-(9,9’-dihexyloxyfluorene)]-alt-[4,7-di(thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-d]pyridazine]}(POFDTTDP), and poly{[2,6-(4,4-dihexyl)-4H-cyclopenta[2,1-b;3,4-b’]-dithiophene)-alt-[4-(1,3,4-thiadiaz ol-2-yl)-7-(thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-d]pyridazine]}(PCPTTTDP) were designed and computed by density function theory (DFT). The electronic, optical and photovoltaic properties and charge transport rates were investigated. The reorganization energies for holes and electrons are around0.11eV and0.08eV, respectively. It indicates that PFDTTDP, POFDTTDP and PCPTTTDP are good candidates for donor material. Especially, when6,6-phenyl-C61-butyric acid methyl ester (PC61BM) functions as acceptor, PCPTTTDP has the most appropriate highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy, and has the broadest absorption in the near-infrared region.In Chapter4, by simulating the molecular structure of9,9’-diphenyl-9H,9’H-2,3’-bicarbazole (BCzPh), a new series of host molecules based on3,3’-bicarbazole derivatives were designed. Density functional theory calculations were performed to reveal their relationship between molecular structures and optoelectronic properties as host materials with blue emitter bis[(4,6-difluorophenyl) pyridinato-N,C2’] iridium(III) picolinate (FIrpic), green emitter fac-tris-(2-phenylpyridine) iridium (Ir(ppy)3) and red emitter tris(1-phenylisoquinolinolato-C2,N)iridium-(III)(Ir(piq)3) used as guest material. The electronic structures in ground states, cationic and anionic states, and lowest triplet states of these designed molecules have been studied from following aspects:the frontier molecular orbitals, electron properties including ionization potentials (IPs), electron affinities (EAs), reorganization energies (λ), spin density (SD) distributions and natural transition orbitals (NTO) at the lowest triplet states, excitation energies in the singlet/triplet (Es0-s1/Eso-T1) states, as well as triplet exciton generation fraction. Their photoelectronic properties can be effectively tuned by chemical modifications of the3,3’-bicarbazole through different substituent groups at N atom. The results underline that:the designed BCZ derivatives can fulfill the requirements of the host materials for phosphorescent organic light-emitting diodes (PhOLEDs).In Chapter5, after investigation on the properties of Dinaphetho[2,3-b:2’3’-f]thieno[3,2-b]-thiophene(DNTT), we introduced cyano groups symmetrically into DNTT. Through comparison on the hole reorganization energy, the best candidates: DNTTT2CN and DNTT4CN were elected. Based on the optimization structure, their electronic properties (the reorganization energy, frontier molecular orbitals, ionization potential and electronic affinity) were calculated. What’s more, we performed crystal structure prediction by using the polymorph predictior (PP) module in Material Studio software. The results indicated that introducing cyano groups into the DNTT framework is a good strategy to improve the charge transfer rate.