AN alternative to silicon-based computing has been cooked up by Italian and
Portuguese chemists. They are making molecules that can be switched between a
pair of states鈥攋ust like computer memory鈥攁nd could one day be used
to store data in a fraction of the space needed by existing silicon chips.
Vincenzo Balzani at the University of Bologna and Fernando Pina of the New
University of Lisbon are using an exotic salt called 4鈥�-methoxyflavylium
perchlorate to make a miniature molecular memory. The flavylium unit has a
structure similar to anthocyanins, the pigments that give many fruits and
flowers their colour.
The salt solution has to be prepared in the dark, and is initially
colourless. But when it is exposed to light, one of the compound鈥檚 oxygen atoms
gains enough energy to move to a new position, altering the molecule鈥檚 structure
and turning the salt yellow.
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The researchers say this effect can be used to record or 鈥渨rite鈥� binary data.
Once it has been transformed into its yellow form, the 4鈥�-methoxyflavylium ion
remains in this state as long as it is in an acidic solution. Light has no
effect on the coloured ion, so it can be optically detected or 鈥渞ead鈥� without
being destroyed. But heating the solution, or making it less acidic, returns the
ion to its original colourless form.
Balzani says that 4鈥�-methoxyflavylium perchlorate is the first known compound
that can be locked or unlocked by changing its temperature or acidity. 鈥淚t鈥檚 a
completely well-described system that goes both ways,鈥� he says. 鈥淵ou can write
and lock, then go back and erase and it鈥檚 ready to write again.鈥�
The next step for Balzani and colleagues is turning their aqueous systems
into solid-state forms, such as a film or ordered array of molecules. So far, no
one has achieved this and Balzani says it could be 20 years before they do.
William Pietro of York University in Ontario says that if a
molecular memory could be developed it would have many uses. It could act in
detectors, responding to particular chemicals in the environment or be used in
implants to trigger insulin infusion devices. 鈥淏ut analogies with what exists
are too limiting,鈥� he says. 鈥淲ith molecular electronics we鈥檒l be able to make
devices which are heretofore unknown.鈥�