Theoretical Studies On The Structures And Absorption Spectra Of 5-(2-pyridyl) Pyrazolate Boron Complexes And 1,3,4-oxadiazole Derivatives

With the aim to explore the nature of OLED materials, the molecular structure and the optical properties of ?Ph and t-Bu Substituted 5-(2-pyridyl) Pyrazolate Boron complexes as well as the electro-withdrawing groups substituted OXD-X derivatives have been investigated by quantum chemistry calculations. The results suggest new theoretical basis and direction for design of novel organic materials. Our work mainly focuses on two aspects:1. The molecular structure, electronic structure and absorption characters of ?Ph and t-Bu substituted 5-(2-pyridyl) pyrazole boron complexes, namely, 2d, 2e, 2d-1 and 2e-1 were theoretically studied using density functional theory (DFT). The optimized results show that the four compounds are four-coordinate organic compounds with C1 symmetry. The boron atom has a typical tetrahedral geometry with the adjacent atoms. In 2d and 2e, the pyrazole ring is functioned as a hole transport group and the pyridyl ring as a electron transport group. In 2d-1 and 2e-1, the hole transport groups are phenyl ring (1) and the electron transport groups are still pyridyl rings. The TD-DFT results show that the main transitions of 2d, 2e and 2d-1 correspond to the intraligandπ→π* character. As the case of 2e-1, the main transition can be assigned as a mixed ligand-to-ligand/interligand charge transfer.2. From the view point of molecular design, we introduced series of electro-withdrawing substituted groups (-CN, -CF3 and -NO2) in the side chain of OXD-X and compared the relative properties with the alkoxy group(?O(CH2)n-1CH3, n=3, 7) substituted derivatives. The molecular structure and electronic structure of the 1,3,4-oxadiazole derivatives were theoretically studied using density functional theory (DFT). The optimized results show that introducing alkoxy chain, ?CF3, ?CN and ?NO2 on central benzene ring has little effect on theπ-conjugated backbone of the whole molecular. The electronic structure analysis shows that the introduction of electro-withdrawing groups (?CF3, ?CN, ?NO2) results in a large decrease on the energy levels of the FMOs with respect to the corresponding electro-donating groups. The TD-DFT results show that compared with alkoxy substituted derivatives, introducing electro-withdrawing groups on the central benzene ring mainly leads to the red shift of the absorption wavelengths. In addition, the absorption spectra of OXD-N can be further modulated through adjusting the position or the quantity of fluorin.