Dynamic anti-counterfeiting security features using multicolor dianthryl sulfoxides†
A new concept for difficult-to-replicate security inks for use in advanced anti-counterfeiting applications is presented. Inks fabricated from a mixture of photoactive dyes result in a unique fluorescent color upon irradiation that differs from the starting fluorescence. The dyes are substituted 9,9′-dianthryl sulfoxides that undergo photochemical extrusion of a sulfoxide moiety (SO) to produce emissive red, blue, and green emitters. The resulting emissive feature has specific Commission international de l'éclairage (CIE) coordinates that are used for authentication. Additionally, the temporal evolution of the fluorescence can be monitored, introducing a dynamic nature to these security features. The three compounds show different rates of photoconversion dependent on the irradiation wavelength, allowing selective wavelengths for activation to be used for additional security. CIE coordinates can be extracted from patches containing the three compounds using an inexpensive, commercially available smartphone application (app) and compared against a known value to confirm the validity of the method.