Effect of molecular rotation upon charge transport between disordered carbazole units

A calculation of intermolecular transfer integrals J for carbazole molecules shows that J varies by orders of magnitude when the molecular planes are rotated. The angular variation of J is used to estimate the corresponding changes in the transition rates. It is suggested that in certain cases the electronic transition occurs after thermally activated hindered rotation. Furthermore, the rotational energy barrier may be a principal component of the rather large electronic transport activation energy which is observed experimentally when carriers move by hopping in certain amorphous organic materials.