Influence of Molecular Packing on Intramolecular Reorganization Energy: A Case Study of Small Molecules

Abstract

The reorganization energy is one important parameter regarding the charge transfer in organic semiconductors. In the past, the influence of the molecular packing on the intramolecular reorganization energy was commonly neglected in theoretical estimations. Here, the quantum mechanic/molecular mechanic (qm/mm) method is used to study this influence for four small molecules: N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD), N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (NPB), 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP), and 4,7-diphenyl-1,10-phenanthroline (Bphen). An approximate linear relationship between the intramolecular reorganization energy and the change of the torsion angle during the molecular relaxation which causes the most steric hindrance is found. Furthermore, reorganization energies from qm/mm calculations are smaller depending on the degree of reduced conformational change.