Energetics mer/fac isomers In metal tris(8-hydroxyquinoline) dictates: Implications on charge conduction in organic light-emitting devices

摘要

Electronic structure calculations for the mer and fac-isomers of aluminum tris(8-hydroxyquinoline) (Alq{sub}3) and the methyl substituted series, nMeq{sub}3Al (n = 3 - 7) are presented. From these data, we estimate their relative abundances in Alq{sub}3 thin films and (he resultant trap state energies, Ab initio computations performed at the SCF level suggest a significantly higher stability (6 - 7.5 kcal/mol) of the mer-isomer over (lie facial form, whereas MP2 treatment of electron correlation effects lowers the difference to (4-4.5 kcal/mol). Substitution of the Al{sup}(+3) metal ion with the larger ions Ga{sup}(+3) and In{sup}(+3) increases (lie energetic preference of the meridiannal form by 2.7 kcal/mol and decreases it by 0.8 kcal/mol, respectively. Trap state energies calculated by previously proposed methodologies show little difference between mer and fac trap slates. These results suggest that the existence of the facial isomer in thin films of metal tris-quinolates is unlikely to significantly affect charge conduction.