| In the past decades, organic charge-transporting materials with π-conjugated molecules are widely studied and used as the components of organic electronic devices such as organic photovoltaic cells, organic light-emitting diodes, organic field-effect transistors and various types of sensors. Organic materials have significant advantages such as low cost, light weight, easy processability, mechanical flexibility and large-area production, which have received intense research attention. Currently, they still have many limitations, for example, the carrier mobility in organic materials is much lower than that in inorganic ones. These prompt us to study intensively on the electronic processes in organic materials, including different carrier transport mechanism in different materials. Because the photoelectrical properties are determined by the construction of organic materials, we studied the properties of several molecules composing different systems in the thesis, such as electronic structure and the impact of intermolecular weak interaction on the molecular packing and carrier transport. It is our purpose to understand the relationship between structure and property and to reveal the nature of these materials, thus our findings would provide essential ideas and theoretical foundation for design and prediction of novel organic semiconductor materials.The thesis is divided into five chapters. Chapter 1 is an instruction, and we briefly introduced the advantage and application of organic electronic materials, explained the organic charge transport materials and carrier transport mechanism, and showed the significance of theoretical study on the development of organic semiconductor materials. Chapter 2 is the theoretical foundation and calculation method, including several quantum mechanical principles and primary method of quantum chemistry calculations. From chapter 3 to chapter 6, we systematically investigated and discussed the relationship between molecular structures and photoelectrical properties for different molecular systems. The specific research content of this thesis is as follows:1. Theoretical study on the electronic structures and properties of diindolocarbazole isomersThe comparative analysis of the optimized geometries, electronic properties, frontier molecular orbitals, ionization potentials, electron affinities, reorganization energies, and absorption and emission spectra for 23 diindolecarbazole isomers was performed by DFT, TD-DFT methods. The configuration of these isomers is different in the linked position of N atoms in pyrrole sections on both sides of the benzene. To study the impact of different linkage patterns on the photoelectric properties of the isomers is very crucial for the molecular design and performance improvement of new functional materials. It is notable that the configuration of 1mm, 2mp, and 3pp are similar, their primary difference is the different orientation of the N atoms, but it turns out diverse in their electronic and optical properties. That is, 1mm, 2mp and 3pp favor the electron transport, balance charge transport, and the hole transport, respectively in according to this work. Otherwise, 3pp could be easily modulated as blue light emitting materials.2. The impact of molecular stacking interactions on the electronic structure and charge transport properties in distyrylbenzene(DSB-) based D–A complexes: a theoretical studyWe investigated the geometric and electronic structures of five monomers based distyrylbenzene, as well as their intermolecular interaction energies, frontier molecular orbitals and charge transfer properties of three D–A models influenced by the configuration of molecular pairs. With respect to the mixed stacked D–A charge transfer(CT) crystals, the favored charge transport direction coincides with the stacking direction, thus the intermolecular orientation of the stacking direction basically determines the charge transport properties. The intermolecular electrostatic interactions caused by electron-withdrawing/ electron-donating effect of substituents play a major role in π-stacking, which directly influence on molecular stacking arrangements of D–A crystals. The CT complexes of D1–A1 have been demonstrated as good ambipolar materials; while the complexes of D2–A2 and D2–A2’ should act as n-type organic semiconductor materials by the calculations in this work. Moreover, they could also act as good ambipolar materials similar to D1–A1 complexes by tuning the crystal growth conditions.3. The impact of substituents in corannulene and sumanene derivatives on the molecular assemblings and charge transport properties—a theoretical study with a dimer modelWe have theoretically investigated the substituent effect on the structures, intermolecular interactions and charge transport properties of a series of curved corannulene and sumanene derivatives. Our findings would facilitate the future design and preparation of these corannulenes and sumanenes derivatives as novel organic semiconductor materials. The results show that: the S-series should possess regular columnar stacking more easily than C-series as the crystal forms. The C-series dimers are more sensitive to the introduced substituents. The values of electron mobility are significantly larger than the hole mobility for all the configurations of the C-series; moreover, compared with the anti-type configuration, the syn-type configuration should benefit the charge transport. It is notable from our theoretical study that, the pristine corannulene dimer with eclipsed configuration has the nature of superior charge transport properties. With introduction of the electron-withdrawing substituents in pristine corannulene, the crystal structure can be tuned to ordered columnar stacking, which effectively increase the actual carrier mobility. On the whole, the C-series has superior electron transport properties; the phenyl substituted S-series show the potential of hole transport, while the benzyl substituted ones should be more beneficial to the electron or ambipolar transport.
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