Information Technology Reference
In-Depth Information
Nevertheless, the idea of frequency-selective recording of information has not
lost its appeal until now. Active search is ongoing for novel memory architectures
and new materials which will be capable of acting as memory devices of giant
capacity.
3.5 Molecular Memory: Developer Dream or Reality?
Let us return to the molecules in which the switching from one stable state to
another occurs due to electron-conformational transition. The understanding that
they may be promising elements of electronic circuits dates back to the 1980-1990s
of the last century as a result of the rapid development of theoretical foundations of
molecular electronics. The last step that remained to be made was to find the
specific molecules of this type which would meet
the expectations of the
theoreticians.
The capabilities of the synthetic methods of organic chemistry increased dra-
matically in the second half of the last century. The development of the theory of
chemical structure on the basis of quantum-chemical concepts dramatically
increased technical capabilities both of synthesizing new compounds and deter-
mining their structure—all of this together allowed for a synthesis of a number of
molecules, of which synthetic chemists had dreamed for decades. Among them
were the molecules constructed from cycles threaded through each other, i.e.,
chained fragments of cyclic compounds (Fig.
3.35
). Their name—catenanes—is
derived from the Latin word catena (chain). Rotaxanes are structurally similar to
catenanes. In these chemical compounds, a linear chain of molecular fragments
penetrates one or several cyclic groups. Three-dimensional molecular groups at the
ends of the chain preclude the collapse of the molecule due to the elimination of a
cyclic fragment from the chain. Similar structures involving purely mechanical
connection of fragments are called molecules “without a chemical bond.”
Synthesizing such molecules is clearly a very challenging task. Only in the early
1980s of the last century, a group of French synthetic chemists proposed funda-
mentally new ways of synthesis. Without going into details, we note that the
synthesis was based on the idea of self-organization of the molecule's structure
and on the analogy with the biological principles of the synthesis of large
molecules.
It is these molecules of catenanes and rotaxanes that turned out to be the basis of
a breakthrough in the creation of molecular electronic circuits in the end of the past
century and in the beginning of the current century. It was initiated by the well-
known American company Hewlett-Packard and the University of California, Los
Angeles.
Over the past decades, Hewlett-Packard took interest in developments in the area
of molecular technologies. This interest dramatically increased in the late 1990s,
particularly after Stan Williams, a physicist at
the company's research lab,
