Ring formation in evaporating porphyrin derivative solutions

The formation of micrometer-size, ring-shaped structures is studied in evap orating solutions of porphyrin-based molecules on glass. Solute concentrati on, solution and substrate temperature, vapor pressure, and solvent are var ied. The molecular arrangements on the substrate are monitored by confocal fluorescence microscopy (CFM), atomic force microscopy (AFM), and near-fiel d scanning optical microscopy (NSOM). From experiment, a nonequilibrium mor phology diagram fell the observed structures is deduced as a function of so lute concentration and evaporation time. The mechanisms involved in ring fo rmation are discussed on the basis of solvent and solute dynamics.