Characterization of Domain Ordering in Polymer and Dendrimer Thin Films Using Photoluminescence and Third Harmonic Generation (THG) Near-field Scanning Optical Microscopy (NSOM)

We have utilized the high spatial resolution of near-field scanning optical microscopy (NSOM) to characterize nanoscopic electronic inhomogeneity in as-cast thin films of a light-harvesting dendrimer consisting of coumarin-343 (core) and coumarin-2 (peripheral) chromophores and in thermally annealed thin films of the semiconductive polymer poly(2-methoxy5-(20-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV). Using photoluminescence (PL) and third harmonic generation (THG) NSOM techniques, we have observed nanoscopic domains in these films that exhibit increased delocalization in the excited (using PL) and ground states (using THG). In addition, we have developed a procedure for examining NSOM images via calculation of radial distribution functions (RDFs). RDF analysis of the PL and THG NSOM images indicates that the domains exhibit correlated structure in annealed MEH-PPV films while the light-harvesting dendrimeric material does not. The existence or absence of such nanoscopic amorphous structure can be understood in terms of the molecular structure of each material. [DOI: 10.1143/JJAP.42.4799]