Occupied and unoccupied electronic levels in organic p-conjugated molecules: comparison between experiment and theory

Occupied and unoccupied densities of states of p-conjugated molecules measured via ultraviolet photoemission spectroscopy and inverse photoemission spectroscopy, respectively, are compared with corresponding densities of states Ž . calculated using the semi-empirical Hartree–Fock intermediate neglect of differential overlap INDO method. Excellent Ž . agreement is obtained for both occupied and unoccupied levels for PTCDA 3,4,9,10-perylenetetracarboxylic dianhydride , Ž X X Ž . X Y . Ž Ž . . a-NPD N,N -diphenyl-N,N -bis l-naphthyl -l,l biphenyl-4,4 diamine , and Alq tris 8-hydroxy-quinoline aluminum . The 3 results provide a full description of the electronic structure of these molecules and demonstrate that semi-empirical techniques can be successfully applied to describe the unoccupied levels of these molecules. q 2000 Elsevier Science B.V. All rights reserved.