MESOSTRUCTNRE OF EVAPORATED PORPHYRIN THIN-FILMS - PORPHYRIN WHEEL FORMATION

The formation mechanism of ring-shaped assemblies (wheels) obtained fr om the evaporation of solutions of 15,20-tris(4-hexadecyloxyphenyl)por phyrin)platinum dichloride (PtP) has been studied by a variety of spec troscopic and microscopic techniques, including confocal fluorescence microscopy (CFM), atomic force microscopy (AFM), and near-field scanni ng optical microscopy (NSOM). Ring-shaped structures have been obtaine d by deposition of CHCl3 solutions on glass, and a strong dependence o f ring shape and size on the initial PtP concentration has been observ ed. Addition of methanol (MeOH) to the solution inhibited ring formati on if the content of MeOH was higher than 10% in volume. Depositions o f CHCl3 solutions on graphite instead of an glass exhibited more perfe ct circular ring structures, Polarization and local time-resolved meas urements of the fluorescence at the edge of the rings demonstrated, ho wever that the rings have similar spectroscopic properties on both sub strates. Scanning probe microscopy techniques (AFM and NSOM) gave deta iled information on the morphology of the ring. The size of the porphy rin wheels varied from 10 nm to several mu m in diameter and between 1 0 and 200 nm in height. NSOM experiments on the nanoscale optical prop erties of the samples indicated that the assemblies are organized on t he nanometer scale due to small molecular aggregates. Additionally, th e effect of the porphyrin (PtP) concentration on the spectroscopic and scattering propel-ties of the PIP solutions revealed that molecular a ggregates are formed prior to evaporation. The implications of these r esults on the ring formation mechanism are discussed in this paper.