Fabrication of microspheres from phthalimide-substituted porphyrin derivatives.

Microspheres were fabricated from phthalimide-substituted porphyrin derivatives. Microscopic analysis showed that the structures of the supramolecular assemblies synthesized in the present study were spherical, with diameters in the sub-micrometer to micrometer range. The size of the microspheres could be controlled by changing the concentration of the casting solution. The spectroscopic properties of the microspheres were measured to determine the influence of their structural components. Thermal studies indicated that the temperature at which these structures became unstable was lower than the bulk melting point. During I-V measurements on devices composed of these microspheres, it was found that the current increased upon light irradiation, and the characteristic photoresponse properties of these devices were reproducible.

Preparation of organic nanoscrews from simple porphyrin derivatives.

Twisted supramolecular assemblies "nanoscrews", were prepared by using simple porphyrin derivatives and acetonitrile solvent. The electrical properties of the assemblies were measured by using microgap electrodes. The nanoscrew had conductivity and showed photo-current. By changing the solvent, the pitch of the screws and their aggregation shapes could be controlled.

Synthesis of dendron-protected porphyrin wires and preparation of a one-dimensional assembly of gold nanoparticles chemically linked to the pi-conjugated wires.

A one-dimensional assembly of gold nanoparticles chemically bonded to pi-conjugated porphyrin polymers was prepared on a chemically modified glass surface and on an undoped naturally oxidized silicon surface by the following methods: pi-conjugated porphyrin polymers were prepared by oxidative coupling of 5,15-diethynyl-10,20-bis-((4-dendron)phenyl) porphyrin (6), and its homologues (larger than 40-mer) were collected by analytical gel permeation chromatography (GPC). The porphyrin polymers (>40-mer) were deposited using the Langmuir-Blodgett (LB) method on substrate surfaces, which were then soaked in a solution of gold nanoparticles (2.7 +/- 0.8 nm) protected with t-dodecanethiol and 4-pyridineethanethiol. The topographical images of the surface observed by tapping mode atomic force microscopy (AFM) showed that the polymers could be dispersed on both substrates, with a height of 2.8 +/- 0.5 nm on the modified glass and 3.1 +/- 0.5 nm on silicon. The height clearly increased after soaking in the gold nanoparticle solution, to 5.3 +/- 0.5 nm on glass and 5.4 +/- 0.7 nm on silicon. The differences in height (2.5 nm on glass and 2.3 nm on silicon) corresponded to the diameter of the gold nanoparticles bonded to the porphyrin polymers. The distance between gold nanoparticles observed in scanning electron microscopic images was ca. 5 nm, indicating that they were bonded at every four or five porphyrin units.

Electronic properties of a single-walled carbon nanotube/150mer-porphyrin system measured by point-contact current imaging atomic force microscopy.

The electronic properties of a single-walled carbon nanotube/150mer of porphyrin polymer wire system were investigated. Current-voltage (I-V) curves were measured simultaneously along with topographic observations using point-contact current imaging atomic force microscopy. Symmetric I-V curves were obtained at bare single-walled carbon nanotubes but characteristic asymmetrical rectifying behavior was found at the single-walled carbon nanotube/150mer-porphyrin junctions. This finding is of key importance for the development of new nanoscale molecular electronic devices.