Multistate/Multifunctional Molecular-Level Systems: Light and pH Switching between the Various Forms of a Synthetic Flavylium Salt

An optical memory device with multiple storage in two different memory levels and nondestructive readout capacity requires the properties exhibited by the 4′-hydroxyflavylium ion, which can exist in several forms (multistate) that can be interconverted by more than one type of external stimulus (multifunctional), as depicted on the right. Its intricate network of light- and/or pH-induced transformations form a basis for simple logic operations.