Theoretical Investigations On The Photoelectric Properties Of Organic Semiconductor Heterocyclic Modified

Recently, organic optoelectronic materials have attracted increasing attention due to manyadvantages, such as wide variety of sources, low production costs, flexible and large displays. Manyexcellent materials have been applied in some photoelectronic devices, such as organiclight-emitting diodes (OLED), organic field effect transistors (OFET), organic photovoltaic cells(OPV), and so on, and they also have been demonstrated superior performance. Compared withinorganic materials, organic photoelectronic materials have complexities of molecular structures,varieties of molecular packings, difficulties of controlling intermolecular interactions and otherproblems, which bring many challenges into the corresponding experimental and theoretical works.In this paper, we combined quantum chemistry with molecular dynamics (MD) simulation toinvestigate the complicated relations among molecular structures, intermolecular interaction andelectron mobility in depth. We hope to provide theoretical supports for understandings andawarenesses of organic photoelectronic materials. Our work mainly includes four aspects asfollows.1. Modifications of the optical properties and charge mobility of spiro-bithiophene (SCPDT) wereinvestigated by time-dependent density functional theory (TD-DFT). Geometry optimizations havebeen performed for the ground state and excited state of bithiophene (BT),4H-cyclopenta[2,1-b:3,4-b0]dithiophene (CPDT) and SCPDT. Vertical excitations and emissiontransition energies have been calculated. The computed vertical and emission transition energies ofBT and CPDT are in good agreement with the experimental data. Compared to CPDT and BT,SCPDT is expected to be an effective EL material with smaller reorganization energy andfluorescence quantum efficiency of non-spiro isolated fragment is preserved in the molecule withspiro-structure.2. The quantum mechanical (QM) and quantum mechanical/molecular mechanical (QM/MM)methods were employed to investigate the photoluminescence and carrier transport properties oftwo bow-shaped thiophene compounds. The optimized geometries were proved to have largedeviation between the single molecule and the solid phase model. The results show that the molecular packings have large influence on the geometrical structures for both systems, but barelyaffect their energy levels of the frontier molecular orbitals and the reorganization energies, thusindicating little effect on the charge transport properties. While, the obvious blue shifts ofabsorption and emission spectra in solid phase compared with the single molecule is related to theintermolecular interactions. Besides, the difference in center thiophene units between twobow-shaped compounds induces the decided differences in photoelectronic properties, especially incarrier transport abilities.3. Modifications of the photoluminescence (PL) excitation spectra of truxene (Tx) and itsheterohomologues were investigated by time-dependent density functional theory (TDDFT) withcc-pVDZ basis set. Geometry optimizations have been performed for the ground state and firstelectronically excited state of truxene (Tx) and its heterohomologues.4. On the basis of the ground state geometry optimized by B3LYP/6-31G*, the calculation ofexcitation energy and oscillator strengths for PCBM are performed using different hybrid of timedepended density functional theory (TDDFT) associated with the influence of basis sets and thepolarity of solvents. Based on an extensive comparison with experimental results, we conclude thatsemi-empirical theory ZINDO is not suitable for calculating the excited state properties of PCBM.For the hybrid functional of TDDFT, with the exact exchange ratio increases, the blue shift of thecorresponding absorption peak becomes greater. The results by CAM-B3LYP and LC-B3LYP arefar away from the experimental value. For the Gaussian type basis sets, the addition of polarizationfunctions in the basis set causes a significantly bathochromic shift of the excitation energy, whilediffuse function does little. The excitation energy of PCBM is lighter depended on the Slater typebasis sets than Gaussian type. The polarization of solvents has little influence on the UV-visproperty of PCBM. The calculation of the UV-vis spectra of the two new PCBM derivatives(TCBM and [70] PCBM) using TD-O3LYP/6-31G*demonstrates that O3LYP functional is themost appropriate in describing the electronic spectroscopic properties of PCBM analogs. Thecalculations for excitation states of PCBM indicates that only the shoulder peak of electronictransitions of excitation states at430nm is contributed by charge transport (CT) from the benzenering to C60cage, others are all identified to Ï€â†'Ï€*like transition.5. Pentacene is a famous p-type organic material with high hole mobility. Here we mainly focus onits conversion of transport property from p-type to n-type when N, O and/or halogen atoms are incorporated from the perspective of theoretical discussion. In comparison with pentacene, thesenew materials containing N, O and/or halogen not only keep the large conjugation and goodplanarity, but also have improvement in molecular packings, in which Ï€-Ï€ packings dominate. It isfound that the vibrations of heteroatoms make important contributions to the reorganizationenergies, and the stabilities of these materials are improved. Meanwhile, the incorporations of N, Oand/or halogen induce a variety of intermolecular interactions, such as Ï€-Ï€, O…H, N…H, F…H andCl…H interactions, which may make important contributions to carrier transport. Furthermore, wedesigned a new molecule with very good stability and high electron mobility. Finally, we hope thatwe can provide theoretical support for designing new high-performance n-type materials throughrevealing the relationship between structures and transport properties.