Charge transport in the glassy state of arylaldehyde and arylketone hydrazones

Abstract

Charge transport in the amorphous glasses of arylaldehyde and arylketone hydrazones has been studied and compared with that in molecularly doped polymer systems. The materials studied include 4-diphenylaminobenzaldehyde diphenylhydrazone, 4-diphenylaminobenzaldehyde methylphenylhydrazone (DPMH), and 4-diphenylaminoacetophenone diphenylhydrazone, which readily form glasses. The hole drift mobilities of these hydrazones in their glassy states were determined to be in the range from 10 −5 to 10 −4 cm 2 V −1 s −1 at an electric field of ca. 10 5 V cm −1 at room temperature, being approximately one order of magnitude greater than those of 50 wt.% molecularly doped polymer systems. The relationship between the molecular structure and charge-transport properties and the effect of the presence of a binder polymer on charge transport are discussed on the basis of the results of electric-field and temperature dependencies of hole drift mobilities. It is shown that electronic and steric perturbations exert an influence on the energetic factor such as activation energy or energetic disorder and that the presence of a binder polymer exerts a significant influence on the pre-exponential factor as well as the energetic factor. Charge transport in a binary glass of the hydrazones and in a supercooled liquid of DPMH has been also studied.