A Fluorescent Polymer for Facile One‐Step Writing of Polychromic Hidden Information in Flexible Films

A poly(para)phenylene conjugated polymer is developed to store information via a quick and facile optical writing method. After exposure to UV light, co‐fluorescence (films with two or more written emission colors –, i.e., “double‐on”) and “on‐off” states are written into the flexible polymer films. The hidden information is invisible under ambient lighting and can only be read with an appropriate light source, optical filter, and/or magnifier, thus providing a level of security for information encoded into the films. The physical and chemical mechanisms are discussed responsible for the rapid fluorescence changes that occur under UV exposure and demonstrate microscale multi‐colored artwork and hidden QR codes written into pliable and freestanding films. Depending on the preparation, the written patterns remained easily visible and stable after exposure to water and to ambient levels of UV background radiation. Information can be encoded onto a fluorescent polymer via facile ultraviolet light exposure. The inscriptions can be written as a single color or in a polychromic format. The polymer can then be removed from the substrate as a freestanding, flexible, transparent film. When exposed to certain wavelengths, the written information becomes visible, especially if aided by the appropriate filter.