Imidazolium‐Functionalized Diacetylene Amphiphiles: Strike a Lighter and Wear Polaroid Glasses to Decipher the Secret Code

Abstract The development of smart inks that change color and transparency in response to external stimuli is very important for various fields, from modern art to safety and anticounterfeiting technology. A uniaxially oriented diacetylene thin film on a macroscopic area is obtained by coating, self‐assembling and topochemical photopolymerizing of imidazolium‐functionalized diacetylenes (M‐DA and T‐DA) and 4,6‐decadiyne ink (70 wt%:20 wt%:10 wt%) exhibiting a lyotropic smectic A liquid‐crystalline phase at room temperature. The color and transparency of letters and symbols written with the DA‐based secret inks change reversibly from blue to red as well as from colorless transparent to black opaque depending on the temperature and polarization axis. A secret code written with thermoresponsive and polarization‐dependent secret inks consisting of imidazolium‐functionalized diacetylenes is successfully deciphered by wearing polaroid glasses and holding a burning torch.