Novel fluorescent security marker. Part I: morphological and optical properties of 2-amino-6-ethoxy-4-[4-(4- morpholinyl)phenyl]-3,5-pyridinedicarbonitrile nanoparticles

Newly synthesized fluorescent nanoparti- cles of 2-amino-6-ethoxy-4-[4-(4-morpholinyl)phenyl]-3, 5-pyridinedicarbonitrile have been developed and characterized for possible applications as security marker in paper documents. Nanoparticles have been prepared by reprecipitation in water under sonication. The size and the shape of these nanoparticles, charac- terized by light scattering and atomic force micros- copy, have been found to be highly dependent on sonication power. Typical sizes range from tens to hundreds of nanometers. Furthermore, a remarkable increase in the fluorescence yield has been observed as nanoparticles sizes decrease. Finally, all of the above features, together with the striking stability of optical and mechanical properties over the course of months, allow for straightforward applications that rely on strong and stable fluorescence such as marking impor- tant or valuable documents.