Metal-free functionalized stilbene crystals exhibit silver luster

Abstract

We herein report a new class of metal-free pigments based on low molecular weight functionalized stilbene derivatives that exhibit silver luster. These derivatives crystallize in very flat platelet shapes with the plain faces of the crystals easily stacked through the filtering process, resulting in multiply-stacked plain faces and high specular reflection over the entire visible wavelength range. Morphological characterization shows that the aspect ratio between the maximum diagonal and thickness of the plain face was at least 20, with surface roughness on the molecular scale. Crystal structure analyses suggest that preferential growth of the plain face is due to a large d-spacing between planar stilbene molecules that are arranged in a herringbone pattern. The specular reflectance of functionalized stilbene crystals was 10–16%, with color coordinates close to those of silver metal. These results suggest that crystals of the functionalized stilbene derivatives are promising dye or pigment materials for use in inks for printing applications.