Molecular logic is an interdisciplinary research field, which has captured worldwide interest. This tutorial review gives a brief introduction into molecular logic and Boolean algebra. This serves as the basis for a discussion of the state-of-the-art and future challenges in the field. Representative examples from the most recent literature including adders/subtractors, multiplexers/demultiplexers, encoders/decoders, and sequential logic devices (keypad locks) are highlighted. Other horizons, such as the utility of molecular logic in bio-related applications, are discussed as well.

Ones and zeros can be handled by molecules through the input-control of their signaling features. The progress in this exciting field during the last five years is covered in this tutorial review.

Photochromes are photoswitchable, bistable chromophores which, like transistors, can implement binary logic operations. When several photochromes are combined in one molecule, interactions between them such as energy and electron transfer allow design of simple Boolean logic gates and more complex logic devices with all-photonic inputs and outputs. Selective isomerization of individual photochromes can be achieved using light of different wavelengths, and logic outputs can employ absorption and emission properties at different wavelengths, thus allowing a single molecular species to perform several different functions, even simultaneously. Here, we report a molecule consisting of three linked photochromes that can be configured as AND, XOR, INH, half-adder, half-subtractor, multiplexer, demultiplexer, encoder, decoder, keypad lock, and logically reversible transfer gate logic devices, all with a common initial state. The system demonstrates the advantages of light-responsive molecules as multifunctional, reconfigurable nanoscale logic devices that represent an approach to true molecular information processing units.

Photochromes are chromophores that are reversibly isomerized between two metastable forms using light, or light and heat. When photochromes are covalently linked to other chromophores, they can act as molecular photonic analogues of electronic transistors. As bistable switches, they can be incorporated into the design of molecules capable of binary arithmetic and both combinatorial and sequential digital logic operations. Small ensembles of such molecules can perform analogue signal modulation similar to that carried out by transistor amplifiers. Examples of molecules that perform multiple logic functions, act as control elements for fluorescent reporters, and mimic natural photoregulatory functions are presented.