Morphology and properties of Langmuir films containing tetrakis(cumylphenoxy) phthalocyanines

Abstract

Tetrakis(cumylphenoxy) phthalocyanine, H 2Pc(Cp) 4, and the family of related compounds containing transition metal ions in the center of the macrocyclic ring, MPc(Cp) 4, will spread from organic solvents to give pressure vs. area isotherms typical of monolayers, but classical monomolecular films are not formed. Mixed films containing a classical component as a transfer promoter, such as stearamide, produce Langmuir-Blodgett (LB) multilayers of better quality than the MPc(Cp) 4 compounds alone. As a structural model, a simple mixed film containing stacked, ordered MPc(Cp) 4 molecules was originally postulated, but more recent observations by transmission electron microscopy and by IR reflectance-absorbance spectroscopy have revealed a more complex and less well-ordered morphology than previously suspected. In mixed films transferred by the LB technique, a two-dimensional colloidal dispersion of MPc(Cp) 4 aggregates is formed. Disk-like aggregates more than one monomolecular layer thick are observed in single-component films and are also seen dispersed in the second component of mixed films. Differential scanning calorimetry also suggests a significant degree of phase separation in the two-component LB films. Small melting point depressions relative to the melting points of single-component monolayers indicate that the melting points of two-component films containing MPc(Cp) 4 are determined by the transfer promoters.