Molecular logic by optical spectroscopy with output transfer by charge migration along a peptide

Computing on the (sub) nanoscale is discussed and illustrated by a specific example of charge transfer along a molecular frame. The general research program is to implement an entire finite state logic machine on a molecule. It is proposed to do so in stages. The first stage is to implement Boolean logic circuits on a single molecule. This has already been achieved up to the level of a full adder. Our current work seeks to implement even more elaborate circuits, to go beyond Boolean logic gates and to go beyond combinational logic circuits to the level of sequential machines. In the longer run it will be necessary to concatenate logical units so that a molecule-like assembly is needed. Here we show by a concrete experimental example that intramolecular concatenation is possible: The molecular backbone is used to move information between two ends of a short peptide. The experiment is a gas phase laser excitation of a molecule with an aromatic chromophore at one end. The absorption by the chromophore localizes the initial excitation. Different outcomes are possible depending on additional inputs. Specifically, charge can be made to migrate to the other end of the molecule. (C) 2002 Elsevier Science B.V. All rights reserved.