Structure and electronic properties of tris(4-hydroxy-1,5-naphthyridinato) aluminum (AlND3) and its methyl derivatives: a theoretical study

Abstract

Molecular structures of the ground state (S0) of tris(4-hydroxy-1,5-naphthyridinato) aluminum (AlND3) and its methyl derivatives have been optimized using B3LYP/6-31G(D) and the first singlet excited state (S1) using CIS/6-31G(D) method, respectively. The frontier molecular orbitals characteristics of these Al-complexes have been analyzed systematically in order to understand the electronic transitions. It is seen from these results that in all these complexes, like in earlier reported mer-Alq3, the highest occupied molecular orbital (HOMO) is localized on the pyridine-4-ol ring of A-ligand while lowest unoccupied molecular orbital (LUMO) is on the pyridyl ring of B-ligand for S0 states irrespective of the methyl substitution present on the ligands. The absorption and emission wavelengths have been evaluated at the TD-PBE0/6-31G(D) level and found to be comparable with the experiment. The charge transfer integrals have been calculated for AlND3, and results reveals that electron transport is larger than hole transport. The reorganization energies have been calculated at B3LYP/6-31G(D) level for these complexes, and the results show that the charge mobilities of these complexes are comparable with mer-Alq3.