Intermolecular- and Intramolecular-Level Logic Devices

The design is discussed of molecule-based logic circuits where each action implements much more than a switch. Results to date that have been validated by proof of concept experiments including on the one hand the implementation of combinational circuits on a single molecule and, on the other hand, the inter- and intra-molecular communication of the results of logic operations. A complementary and even more powerful design is that of a finite-state logic machine on a single molecule and beyond that, programming of a single molecule. Both electrical and optical addressing and readout are discussed, the advantage being that it is not necessary to be able to address many states as with three states a full adder can already be achieved. The chapter concludes with some perspectives for the future and a list of desiderata.