Toward rational designing of n-type materials: Theoretical investigations of mer-Alq3 derivatives

The ground state geometries of the CN and OCH3 derivatives of the meridianal isomer of tris(8-hydroxyquinolinato)aluminum (mer-Alq3) were calculated by density functional theory. The absorption spectra were computed at the TD-PBE0/6-31G* level. We have observed that position for substitution plays important role for absorption properties. The cyano derivatives make the LUMO energy levels lower and the electron affinity increase, thus these derivatives would enhance the electron injection ability. The ionization potentials and electron affinities showed that cyano derivatives would be better hole blockers than methoxy derivatives. The reorganization energies indicate that CN derivatives would enhance the electron mobility while introduction of OCH3 has no effect in the enhancement of electron mobility. We explained the distribution of highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) on different individual ligands.