Supramolecular assemblies of octasubstituted phthalocyanines: Synthesis and characterization.

Our interest in controlling the supramolecular architecture of highly symmetric dyes, which are modified with side chains to improve their solubility in nonaqueous solvents, has stimulated the synthesis of several novel phthalocyanines (Pc's). The synthesis and characterization are reported for new 2,3,9,10,16,17,23,24-octasubstituted metallated phthalocyanines (Pc's), that have ester, amide or ether side chains. The supramolecular ordering of the molecules in solution and as thin films is examined. The Langmuir-Blodgett, absorption, electrochemical, and photoelectrochemical behavior of each octasubstituted Pc derivative is investigated. They are strongly dependent on the hydrophilicity/hydrophobicity balance, the connecting group hybridization, and the electronic character of the side chain. Thin films, formed by casting from solution and evaporation or by LB deposition onto a substrate, are macroscopically well-ordered as indicated by absorption spectroscopy, FTIR spectroscopy, and optical microscopy. Monolayer studies of the Pc's reveal the formation of fibers at pressures that cause collapse of the monolayer. Fibers, several microns long, could be pulled from the surface. Optical microscopy suggests liquid crystalline behavior. Electrochemical studies indicate that the redox processes of each Pc derivative are strongly affected by aggregation, pH, and extent of order within the films. The photoelectrochemical behavior, using cast Pc films on SnS₂ semiconductor electrodes, indicate that the Pc chromophores in the first monolayer have a different orientation than subsequent layers in multilayer structures and that the first layer at the Pc/SnS₂ interface is primarily responsible for charge injection. Finally, molecular modeling is applied to analyze the likely supramolecular ordering of the molecules