The search for molecular electronics has induced increasing interests in single molecule measurements, and generated a lot of feats to clarify the individual molecule behaviors as electronic circuitries such as switches, wires, transistors, and so on. Now, to make more complex circuitry or molecular computer from them, self-assembly has attracted much attention. However, the development to put the molecular components together on a substrate with keeping the individual properties intact in a self-assembling manner is challenging, and few successful examples have been reported so far. As one of approaches to fix the single molecule, we propose the way to construct nanospace around single molecule using dendrimer architectures so that the individual molecule behaves without intervention from the neighbors, like electrical cross-talk, mechanical contact and the like.
Our new method is as follows: (1)firstly, synthesized on Au or Si surfaces is the self-assembled monolayer of dendrimers having sticky cores to the surface, which turn to be confined reactive-sites or molecular-circuitries to the surface; (2)next, the dendron spacers are removed by external stimuli such as light, chemical species, etc., so that the isolated reactive sites or molecular circuitries form a nanoarray with the distance depending on the size of the dendrons.
In order to establish this method, we synthesized dendrimers with an ester-linkage that is base-labile, between thioctic acid core and benzylether dendrons. The self-assembled monolayers on Au substrates were obtained by a conventional method, just soaking the substrates into an organic solution containing the dendrimers. Then, the substrates were subjected to a KOH methanolic solution containing toluenethiol, which is thought to serve as a matrix to discourage the movement of the remaining sites on the surface after the hydrolysis. We characterized these surfaces by FT-IR spectroscopic and contact-angle measurement, and AFM observation. As a result, non-contact mode AFM images of the resulting surfaces revealed that there were some arranged areas of the features with the distance of about 6 nm and the height of about 0.8 nm, indicating that the remaining acids on some parts of the surface form a nanoarray with the distance of the dendrons size. We are now searching for the optimal condition to fabricate the well-ordered nanoarray of isolated single-molecules.
We will report on the results obtained through a series of the above studies, and also discuss some other examples using different-type cores.
National Institute of Advanced Industrial Science and Technology
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