The electronic structures and properties of Alq3 and NPB molecules in organic light emitting devices: Decompositions of density of states

A decomposition treatment of density of states in combination with PM3 molecular orbital calculations was used to reveal the fingerprints of electronic structures of two prototypical electroluminescent molecules, tris(8-hydroxy-quinoline)aluminum (Alq₃) and N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′- diamine (NPB). High convenience and accuracy of such a treatment were found for these large organic molecules in the determinations of (1) the distribution of important molecular orbitals such as the highest occupied orbital and the lowest unoccupied orbital; (2) the contribution to valence and conduction bands as well as gap states from constituent atoms, and thus the attribution of ultraviolet photoemission spectrum; (3) the sites and properties of reaction and excitation of a molecule; and (4) the localization property of electronic states. In particular, this study indicates that Alq₃ is most possibly attacked by other atoms at the oxygen atoms while the reaction site for NPB is at the nitrogen atom. © 2000 American Institute of Physics.