Comparison of the electrophotographic properties of a family of hydrazone charge transport molecules

Abstract

A study has been made of a family of six substituted aminobenzaldehyde-hydrazones in which molecular properties are related to electrophotographic function. The transport molecules are characterized by optical absorption, oxidation potential and strength of charge transfer complexation with the polymer binder. The evaluation of electrophotographic function includes charge transport mobility, charge injection efficiency from the generation layer and residual voltage. Hole mobilities in these materials differ by several orders of magnitude. The mobility is not (simply) correlated with any molecular electronic property such as oxidation potential or absorption wavelength. The most relevant molecular parameter appears to be number of phenyl substituents on the amine and hydrazine nitrogen atoms. The polymer binder also affects the mobility. A solid solution in of DEH in polyarylate, which is a weak electron acceptor and forms a weak charge transfer complex with the donor transport molecule, has a lower activation energy for transport than DEH in polycarbonate which forms no such complex. The charge injection efficiency has been related, in the past, to the oxidation potential (Eox) of the transport molecule. It is shown here that Eox correlates better with the residual voltage, and a simple model is developed to explain the relationship.