ARTIFICIAL PHOTOSYNTHETIC OPTO-ELECTRONIC SWITCH OR MEMORY

The effects of magnetic fields on the lifetimes of pairs of free radicals formed by exposure to light and the yields of the corresponding chemical products have been studied for many years. Magnetic field effects are generally observable in radical pair systems wherein the donors and acceptors freely diffuse in solution, or in bi-radicals where the radicals are linked by flexible chains such as polymethylene groups.Consequently, rigid donor-acceptor assemblies, or those in media such as low-temperature glasses where rapid diffusion is impeded, typically do not demonstrate magnetic field effects on radical pairs. This hinders the use of such effects in the design of molecular-scale electronic components that must function in rigid media. By employing certain multi-step electron transfer strategies whereby the electron is moved from the donor to acceptor via an intermediate species, it is possible to avoid the effects of slow diffusivity. The preeminent example of this phenomenon is photosynthesis, where a number of different magnetic field effects on reaction yields and rates have been observed. Researchers at Arizona State University have discovered and devised a chemical scheme that utilizes these effects as the basis for a magnetically controlled optical or optoelectronic switch or memory. Inputs are light and the magnetic field. Outputs are an optical readout via absorption of the charge-separated state, and/or an electrical readout via a change in current or voltage in electrical contacts to the molecule or an assemblage of molecules.