Abstract: A device is presented having reversibly changeable and optically readable optical properties. The device comprises a substrate having an electrically conductive surface and carrying a redox-active layer structure. The redox-active layer structure may be a monolayer or a multi-layer structure and is configured to have at least one predetermined electronic property including at least one of electrodensity and oxidation state. The electronic property of the layer structure defines an optical property of the structure thereby determining an optical response of the structure to certain incident light. This at least one electronic property is changeable by subjecting the redox-active layer structure to an electric field or to a redox-active material. The device thus enables effecting a change in said electronic property that results in a detectable change in the optical response of the layer structure.