Molecular orientation and electrical behaviour of Langmuir-Blodgett films of phthalocyanine derivatives containing eight alkyl chains

Abstract

Monolayer assemblies ofsome phthalocyanine derivatives with a central conjugated system surrounded by an insulating region of eight alkyl substituents have been produced, and their molecular orientation and electrical behaviour studied. Polarized visible and IR spectra for the multilayers deposited by a horizontal lifting method showed that the phthalocyanine macrocycles were nearly parallel to the surface and the hydrocarbon chains were oriented almost vertically. The perpendicular conductivity was ca. 10^–13 S cm^–1, while the parallel value was ca. 10^–7 S cm^–1. The former increased to 10^–10 S cm^–1 with applied frequencies from 1 mHz to 100 Hz, while the latter changed only slightly. It is considered that electronic hopping conduction between the layers is predominant in the perpendicular direction, depending on the chain length of the alkyl substituents. The enhanced lateral conduction can be ascribed to the molecular arrangements with the adjacent π-electron systems of the phthalocyanines in the plane of the film.