AIDA Nanospace

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It has long been a dream of chemists to carry out the important chemical reactions of living organisms in the laboratory or as practical technology. For instance, in 1912 Italian photochemist Giacomo Ciamician of the University of Bologna wondered whether it would not be advantageous to make better use of radiant energy, such as to make batteries based on photochemical processes.

Molecules continuously recognize and affect one another through chemical and physical interactions. For example, water molecules behave like a gigantic molecule by forming numerous

hydrogen bonds. That water boils at 100C° is not an intrinsic nature of a single water molecule, but is a characteristic of such a gigantic aggregate. Because molecular interactions involve many different forces, certain important reactions such as electron transfer and energy migration occur. But, if one can break some of these interactions or if a molecule can be freed from all of these intermolecular forces, it may eventually exhibit some unexpected properties which are inherent to the molecule itself or its local environment.

Understanding and utilizing this fact was an important step to realizing the dream of Ciamician. In the mid 1980s non-linear hyperbranched macromolecules were first synthesized. Such nanometer-size macromolecules are called dendrimers, which are characterized by a regular tree-like array of branched units. In 1992, Takuzo Aida encapsulated a porphyrin at the center of a cavity consisting of a dendrimer molecule. A porphyrin is a dye-type molecule, like the iron porphyrin that binds molecular oxygen in the heme protein of red blood cells, or the chlorophyll that promotes photosynthesis in green plant cells. In the course of this study, it was found that the cavity of a certain dendrimer, like a biological light-harvesting antenna, traps photons and channels the excitation energy to the interior molecule, whereby certain chemical reactions then take place. A detailed investigation has shown that this reaction occurs only when the dendritic nanocavity has such a closed architecture that it can specially isolate the interior environment from collisional energy dissipation. Such an observation has been extended to the development of novel light-emitting organic diodes for next-generation imaging devices and the potential to utilize photosentizers for photochemical water splitting.

Further, by using a porous inorganic material, Aida and co-workers also succeeded to fabricate crystalline nanofibers of linear polyethylene with an ultrahigh molecular weight (6,200,000) and a diameter of 30 to 50 nanometers. A particular type of silicate material of a honeycomb-like porous framework was utilized as a nanoflask for the polymerization of ethylene, where the produced polymer chains were extruded from the mesopores and then assembled to form extended-chain crystalline polyethylene nanofibers with excellent mechanical properties. The present strategy has been intended to mimic the natural processes for the formation of crystalline fibers, such as cellulose and cocoon, via extrusion through biological nanopores, and has potential for the fabrication of novel polymeric materials from commodity monomers.

These two examples illustrate the great possibilities of restricted nanospaces for developing novel reactions that have never been expected based on the existing knowledge about ordinary bulk systems. Extending this basic idea by changing the size, dimension, and shape of the nanoscopic cavities and pores should result in breakthroughs in science and technology.

Research Director: Dr. Takuzo Aida
(Professor, Department of Chemistry & Biotechnology, Graduate School of Engineering, The University of Tokyo)
Research Term 2000-2005

Strategic sector

The Aida Nanospace project is exploring the basic science of nanoscopic phenomena, and is using this knowledge to study a very wide range of such systems and the chemical reactions that they can promote. Important practical reactions are also being developed. Research falls into three main areas:
 The first area involves the chemical synthesis and utilization of a wide variety of dendritic nanospaces. Dendrimer molecules with a variety of sizes and number of dendrite ridges are being developed, which result in various sizes and shapes of cavities and degree of encapsulation. These structures are also being optimized for channeling the maximum amount of radiation at specific wavelengths. The physics of such confined nanospaces is also being explored.
 The second area concerns the chemical synthesis and utilization of confined metal-coordinated nanocavities and inorganic nanopores for fabricating novel nano-scale optical and electronic materials and devices. An effort is being made to explore the physical properties of the products as potential photo and electronic devices.
 Another area involves the utilization of biological motifs, such as proteins. One important application would be to construct a system that could carry out the photosynthesis process that takes place naturally in plants, thus allowing energy to be harvested in an energy-starved world. Efforts are being made to mimic the biological light-harvesting systems.
 Further, the creation of a system that can focus light energy to produce a hydrogen-releasing reaction is being pursued. Preliminary results have been very encouraging, while implying that efficient hydrogen evolution should be possible. An effective and inexpensive reaction that can release free hydrogen has been long sought for use in fuel cells and other technologies.
 Efforts are also directed to creating a variety of sensing molecules and information-transferring supramolecular systems.

Project Office

c/o National Museum of Emerging Science and Innovation, Research Area 4F
2-41 Aomi, Koto-ku, Tokyo 135-0064, Japan

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Phone:03-3570-9181
FAX:03-3570-9180
E-mail:
aida01erato.jst.go.jp

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