Luminescent sensors and photonic switches

The principles of photochemistry continue to fuel progress in luminescent s ensors and photonic switches. Examples of sensors based on photoinduced ele ctron transfer (PET) are discussed, including those which form the basis of successful systems used in physiology and medicine. More complex formats u sually involve multiple receptors. One progression takes us to lanthanide c omplexes enabled with sensory capabilities. Another path takes us to molecu lar-scale implementation of logic gates such as AND and INHIBIT. Such lumin escent switches can be enriched by combination with nonluminescent cousins. The latter are based on internal charge-transfer excited states (ICT). An example of rudimentary arithmetic at the molecular scale is presented by ru nning a luminescent AND gate in parallel with a nonluminescent XOR gate. Th us, small molecules can process small numbers for the first time outside of our brains.