Dendrimer

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A dendrimer is a molecule with a form like the branches of a tree. The name comes from the Greek "δενδρον"/dendron, meaning "tree." In 1979, the first dendrimer was synthesized by D.A. Tomalia and other researchers at the Dow Chemical Company, and dendrimers have been studied all over the world because their form is unique (Fig. 1).

Figure 1. Dendrimers

Synthesis

In the synthesis of dendrimers, monomers lead to a monodisperse polymer, tree-like, or generational structure. There are two defined methods of dendrimer synthesis, divergent synthesis and convergent synthesis. The former assembles the molecule from the core to the periphery and the latter from the outside to termination at the core.

However, because a repeated reaction which consists of many steps is needed to protect the active site, it is difficult to synthesize dendrimers even if both methods are used. This is why there are obstacles to the synthesis of large quantities of dendrimers.

Properties and applications

The properties of dendrimers are dominated by the functional groups on the molecular surface. For example, a dendrimer can be water-soluble when its end-group is a hydrophilic group, like a carboxyl group. It is theoretically possible to design a water-soluble dendrimer with internal hydrophobicity, which would allow it to carry a hydrophobic drug in its interior.

Another property is that the volume of a dendrimer increases when it has a positive charge. If this property can be applied, dendrimers can be used for drug delivery systems (DDS) that can give medication to the affected part inside a patient's body directly.

Photonic excited molecules

The inside of a dendrimer has a unique chemical environment because of its high density. From this property, it has been discovered that azobenzene is photoisomerized by very weak infrared rays when covered by a dendrimer [1]. Through the discovery of a function that catches light and conveys this energy using excitation of the molecule, attempts have recently been made to synthesize dendrimers that insert porphyrin, absorb light, and photosynthesize artificially. In addition, the development of organic electroluminescent devices and their applications has been undertaken by researchers all over the world.

Reference

[1] Dong-Lin Jiang, Takuzou Aida, Nature 388, 454-456 (1997)

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