Theoretical investigation on the structure and electronic properties of Alq2R (RÂ =Â 8-hydroxyquinoline, OH, phenolate and phenylphenolate) and its derivatives

The structure and electronic properties of 5- and 6-coordinated Al complexes Alq2R (6-coordinated Al complexes: R = q(8-hydroxyquinoline); 5-coordinated Al complexes: R = OH, P (phenolate) and B (phenylphenolate)) were investigated theoretically by means of quantum mechanical calculations based on density functional theory (DFT) and time-dependent DFT (TD-DFT) using the B3LYP functional. Geometry optimizations of the complexes were performed for the ground state (S0) and the lowest exited stated (S1, calculated using the configuration interaction singles (CIS) method). The second ligand (R) of 5-coordinated Al complexes is found to be important contributors in the geometry structure and the charge transport properties of the complexes. In addition, the second ligands substitutes in 5-coordinated Al complexes also noticeable affect the vertical ionizations (VIPs), which will be expected to be used as selective hole-block materials to increase the efficiency and lifetime of the OLED. The nature and the energy of the first singlet-singlet electronic transitions have been obtained from TD-DFT, and radiative lifetimes were calculated as well. As for tuning the spectra properties, it is indicated that the electron-withdrawing methyl at 4-position of quinoline in either 5- or 6-coordinated Al complexes would be more efficient to get blue-light materials, and could obviously affect the radiative lifetimes.