Modulating Fading Time of Photochromic Compounds by Molecular Design for Erasable Inkless Printing and Anti-counterfeiting

Erasable inkless printing and anti-counterfeiting are two important applications of photochromic materials. However, there are few studies that focus on their different requirements of fading time. In this work, a molecular design strategy is used to optimize fading time of viologen analogues by modulating intermolecular interactions. We adopted a zwitterionic viologen analogue which has a short fading time for anti-counterfeiting. Then, by introducing a second ligand containing a benzene ring, a metalloviologen compound is constructed, in which the benzene ring can produce more intermolecular interactions with viologen molecules. This improves the structural rigidity and radical stability, thus resulting in a prolonged fading time for erasable inkless printing. Our work could open a facile avenue to construct photochromic materials to meet different application needs.