Jin-Song Hu, Yu-Guo Guo, Han-Pu Liang, Li-Jun Wan*, Li Jiang

As a “bottom-up” strategy, self-assembly and self-organization are showing ever increasing importance in chemistry, material science, life science and nanotechnology. A wide variety of nanometer or micrometer scale structures and assemblies has been generated by this technique, as a result of understanding and fabricating of living and natural systems from non-living and artificial self-assemblies. The organization of these nanostructures into higher order two or three-dimensional architectures may form the interconnects to the macroscopic world, and meet the requirement of many objectives with advanced functions in science and technology, such as sensor, microelectronic and microelectromechanical systems, and microanalytical and microsynthetic devices, just like the construction of biological world from cell to tissue, to organ, and then to body.

At the Institute of Chemistry, Chinese Academy of Sciences, Beijing, the group leaded by Prof. Li-Jun Wan has found that a new technique creates self-assembled porphyrin hollow hexagonal nanoprisms that can collect into a smectic phase. A part of the related research work has been published in the Journal of American Chemistry Society (2005, Vol. 127, No. 48, 17090-17095), and highlighted by the important international journal of Photonics Spectra (Photonics Spectra, 40 (1), 26 Jan 2006).

When zinc meso-tetra (4-pyridyl) porphyrin (ZnTPyP) is suspended in solution with a surfactant molecule, cetyltrimethylammonium bromide (CTAB), the molecules assemble into hollow tubes with a hexagonal cross section, a wall thickness of 30 nm and an outer diameter of 95 nm. The length of the tubes varies with the relative concentrations of ZnTPyP and CTAB. Furthermore, when the solution is allowed to evaporate, the structures align themselves parallel to each other into a three dimensional smectic suprastructure as a result of dispersivity and regular geometric shape, as shown in the figure. Such a smectic crystal is intriguing for several reasons. For one, it represents one of the few examples of an organic material that can self-assemble into a secondary structure. Also, porphyrins are interesting because they are biologically compatible and exhibit photochemical activity. The self-assembled structure could be useful for photonic crystals, drug-delivery devices and molecular filters.

Owing to the rich catalytic-, photo-, electro-, and biochemical activities, the hexagonal hollow prism-shaped porphyrin nanostructures are expected to be useful in the applications such as catalysis, drug delivery and protection of biological active materials, and might be used as an organic 1D building block to fabricate electronic, optoelectronic and electrochemical nanodevices. The ordered assemblies may opens up exciting avenues for a number of applications from nanoscale optoelectronic devices to catalysis, drug delivery and molecular filtration.

Prof. Li-Jun Wan said that the scientists are working to understand the properties of single hollow hexagonal nanoprisms and trying to find another method to control the secondary structure.

J. Am. Chem. Soc. (2005, Vol. 127, No. 48, 17090-17095)