Molecular orientations in Langmuir-Blodgett and vacuum-deposited films of VO-phthalocyanine

Abstract

Phthalocyanines have long been used as active materials for molecular devices such as chemical sensors. The thin film techniques for phthalocyanines include vacuum deposition (VD), the Langmuir-Blodgett (LB) method, and spraying of a fine suspension, some of which involves procedures with low reproducibility. The physical properties of vanadyl phthalocyanine, however, has received less attention than other transition metal phthalocyanines, mainly because of the complex vanadyl cation and the difficulty in obtaining well-defined thin films. Langmuir-Blodgett (LB) and vacuum-deposited (VD) films of vanadyl tetra t-butyl phthalocyanine (VOTBP) were investigated by electron paramagnetic resonance (EPR) to elucidate their film structure and molecular organization. Angular variation of the EPR spectral position revealed that VOTBP in the LB and VD films orients perpendicular and parallel to the substrate, respectively. The EPR linewidth indicated a two-dimensional spin chain in the LB films and a three-dimensional in the VD films. The order parameters evaluated from the EPR magnetic parameters demonstrated a moderate degree of ordering in both the films.