Molecular switches based on photoconductivity and photochromism

Charge photogeneration in molecular materials involves auto-ionization of the excited state and thermalization of the hot electron, leading to the formation of electron-hole or ion pairs, and thermal dissociation of the pair into free carriers. The ion pairs, due to the molecular dynamics and charge self-trapping processes, can form quasi-stable species with a characteristic optial absorption; thus, switching from the neutral to the ionic phase can occur. In some molecules a reversible rearrangement of atoms, caused by trans-cis isomerization, homolytic bond fission, tautomerism, heterolytic bond cleavage, etc., occurs and a photochromic switching process can take place. Both types of switch can also operate as optical memories.