Fluorescent doughnut-like assembling of wire-type dendrimers depending on their generation numbers and degrees of polymerization

The self-assembled structures by evaporation of tetrahydrofuran (THF) solut ion of wire-type dendrimers have been studied by some spectroscopic and mic roscopic techniques. Doughnut-like structures were obtained for some dendri mers with generation number of 2 and about 28 nm length by depositions thei r THF solutions on a quartz substrate, while yam-like and particle-like str uctures were obtained for other dendrimers. The size of the doughnut struct ure Varied from I to 8 mum 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 assemble d structures and electronic properties in addition to conventional fluoresc ence spectroscopy. Polarization and local fluorescence measurements at some parts of doughnuts and particles were demonstrated, however, no correlatio n between molecular orientation/intermolecular interaction and doughnut str uctures was found. The doughnut formation mechanism is considered on the ba sis of evaporation processes observed from in situ experiments.