Analog applications of photochemical switches

Molecules that change their structure in response to a stimulus such as light or an added chemical can act as molecular switches. Such switches can be chemically linked to other active moieties to create molecular "devices" for various purposes. There has been much activity of late in the use of molecular switches such as photochromes in the construction of molecular logic gates that carry out binary or digital functions. However, ensembles of such molecules can also act as analog devices. Here, examples of a molecular photonic signal transducer and two mimics of photosynthetic photoregulatory processes are discussed. Ensembles of molecules containing photochromes or other molecular switching elements can be used as either binary or analog "devices." Examples of analog applications are presented. The graphic schematically depicts a molecular signal transducer that is an analogue of a transistor amplifier. A blue light input generates green fluorescence output whose amplitude is regulated by a second, red light input.