Theoretical studies on charge transport character and optional properties of Alq3 and its difluorinated derivatives

Abstract

Electronic structures and spectroscopic properties of tris(8-hydroxyquinoline) aluminum (Alq3) and its difluorinated derivatives are studied by using ab initio and DFT methods. The B3LYP and CIS methods have been used to optimize the ground- and excited-state geometries, respectively. Absorption and emission spectra are also calculated by using the time-dependent density functional theory (TD-DFT) based on the ground- and excited-state geometries. We have found that for difluorinated Alq3 the substituents cause energy lowering in the energy levels of the lowest unoccupied molecular orbitals (LUMO) and the electron affinity ( EA) increase, which facilitates injection of the electron carrier from the metal electrode. By comparing with the non-substituted Alq3, 5,6-difluoro-substituted ( 2) and 5,7-difluoro-substituted Alq3 ( 3) undergo slight red-shift in the spectra, while the 6,7-difluoro-substituted Alq3 ( 4) shows blue-shift. In view of the electronic reorganization energy ( λ e), the complexes 2 and 4 are potential materials for electron injection and transport. In addition, the results reveal that important blue luminescence materials can be obtained by applying strong electron-withdrawing substituents at the 6,7-positions of phenoxide.