Theoretical Studies On The Charge Transport Performances Of Thiophene- And Naphthalene-based Organic Materials

Recently, due to many advantages, such as wide variety of sources, low production costs, flexible and large displays, organic optoelectronic materials have been focused on. Many excellent materials have been applied in some optoelectronic devices, such as organic light-emitting diodes (OLED), organic field effect transistors (OFET), organic photovoltaic cells (OPV), and so on, and they also have been demonstrated superior performance. Compared with inorganic materials, organic optoelectronic materials have complexities of molecular structures, varieties of molecular packings, difficulties of controlling intermolecular interactions and other problems, which make the corresponding experimental and theoretical works have many challenges.In this paper, we combined quantum chemistry with molecular dynamics (MD) simulation to investigate the complicated relations among molecular structure, intermolecular interaction and electron mobility in depth. We hope to provide theoretical supports for understandings and awarenesses of organic optoelectronic materials. Our work mainly includes four aspects as follows.1. Comparative theoretical investigation on the fluorescence and charge transport properties of dithienothiophene compounds and their dioxide derivatives was carried out to shed light on the role of the thienyl-S,S-dioxide unit. The phenomenon that fluorescence quantum yield of dioxides was significantly increased through thienyl-S,S-dioxidation, compared with their parents, was analyzed by the evaluations of the radiative decay rates and the radiationless decay rates in theory at the single molecule level and the simulation of absorption spectrum of dimer of 1, which finally suggests that the aggregation effect is the main reason. A preliminary investigation of the transport property of a dioxide was performed by combining the molecular dynamics simulation with dispersion-corrected B3LYP functional to provide insight into the effect of thienyl-S,S-dioxidation on the charge transport.2. The influence of introduction of gold atom on the hole transport property of pentacene was investigated by combining density functional theory (DFT) with Marcus theory, focusing on intramolecular reorganization energy, intermolecular transfer integral, and hole hopping rate. The results show that the main contributions toλtransit from the stretching of C-C bonds to the stretching of Au-Pentacene with Au introduced, and that this transition becomes increasingly intense when the Au atom is near the edge of pentacene. As for transfer integral, the introduction of Au atom results in the decrease of its value arising from the effect of both the geometries and character of frontier orbitals.3. Seven perylene bisimide derivatives with different molecular packings and intermolecular interactions were investigated in detail within Marcus-Levich-Jortner formalism at the level of DFT. Insight into the geometries, the character of the frontier molecular orbitals, the decompositions of reorganization energies, and transfer integrals in different directions was provided to shed light on the relationship between structures and properties. The molecular dynamics (MD) simulations and band structures calculations were also employed to give a multiscale understanding of their transport properties. It is found that compounds, respectively, with typical“brick”packing,π-stacked face-to-face packing, and“herringbone”packing, have larger electron mobilities among these systems and possess different transport dimensionalities.4. Three naphthalene tetracarboxylic diimides (NDI) derivatives with very large electron mobilities and long term ambient stability were investigated employing Marcus–Levich–Jortner formalism at density functional theory (DFT) level. The complicated relationships among molecular packings, intermolecular interactions, and transport properties for these systems were focused on and analyzed through the optimizations of transport pathways and the calculations of intermolecular interaction energies using dispersion-corrected density functional theory (DFT-D). The results show that the transfer integrals are sensitive to the subtle changes of intermolecular relative orientations, especially for core-chlorinated systems, and there is mutual influence between intermolecular interaction and molecular packing. It is found that the molecular packings of these systems determine their electron mobilities. Furthermore, the band structures calculated and the comparisons of mobilities before and after optimization indicate that the intermolecular relative orientations of 2 in the film state may have discrepancies with those in the crystalline state.