Fluorescent Doughnut-Like Assembling of Wire-Type Dendrimers Depending on Their Generation Numbers and Degrees of Polymerization

Abstract

The self-assembled structures by evaporation of tetrahydrofuran (THF) solution of wire-type dendrimers have been studied by some spectroscopic and microscopic techniques. Doughnut-like structures were obtained for some dendrimers with generation number of 2 and about 28 nm length by depositions their THF solutions on a quartz substrate, while yarn-like and particle-like structures were obtained for other dendrimers. The size of the doughnut structure varied from 1 to 8 μm in diameter and between 30 and 150 nm in height. Confocal fluorescence microscopy, atomic force microscopy (AFM), and near-field scanning optical microscopy (NSOM) were applied to elucidate assembled structures and electronic properties in addition to conventional fluorescence spectroscopy. Polarization and local fluorescence measurements at some parts of doughnuts and particles were demonstrated, however, no correlation between molecular orientation/intermolecular interaction and doughnut structures was found. The doughnut formation mechanism is considered on the basis of evaporation processes observed from in situ experiments.