Chapter 9

Molecular Logic Gates

‘I do not fear computers. I fear the lack of them.’

Isaac Asimov

9.1 Introduction

In the preceding chapters various materials and processes have been discussed from the point of view of digital information processing. While these novel materials allow further miniaturization of electronic devices, they still enforce the application of classical electronics paradigms, that is information is encoded in electric pulses and information processing requires control of the electrical conductivity of certain elements. If, however, chemical or optical inputs are directed towards molecular devices, a whole plethora of different information processes is possible and the output information may be also directed into different output channels (cf. Chapter 3). The following sections present the evolution of chemically, optically and electrochemically driven molecular-scale logic gates from the simplest OR gates to multi-state switches and reversible Feynman gates.

9.2 Chemically Driven Logic Gates

Chemically driven molecular logic gates originate from fluorescent sensors with an optical readout. They are usually based on the following photophysical phenomena: photoinduced electron transfer (PET), intramolecular charge transfer (ICT), electronic energy transfer (EET), excimer/exciplex formation and reorganization of the electronic structure of transition-metal-based chromophores/fluorophores [1–8].

The principle of a PET-based chemical switch is shown in Figure ...

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