Investigation on the doping of dyes in single crystalline anhydrous guanine microplatelets and their optical properties

Guanine crystals with a high refractive index (1.85) are widely applied as optical materials in organisms. However, the synthesis of colored guanine crystalline plates doped with different kinds of commercial organic molecules still remains challenging. In this work, guanine crystalline microplatelets with different colors and pearlescent luster were synthesized by doping cationic or molecular dyes into guanine crystals. The synthesized dye-doped guanine crystals were pure β-form anhydrous guanine (β-AG) single crystalline microplatelets and exposed the (100) plane similar to those of biological guanine crystals. Dye-doped β-AG crystals exhibited various colors, such as red, yellow, green, blue and purple, and their aqueous dispersions exhibited bright pearlescent luster. We doped different organic molecules into the crystal lattices and obtained single crystalline β-AG microplatelets with superior pearlescent luster. It was observed that both cationic and neutral molecular dyes with small molar volume could be easily doped into guanine crystals, and the preferential exposure of the (100) plane of guanine crystalline microplatelets was not affected. Moreover, the diffuse reflection intensities of most dye-doped β-AG crystals were up to 80% in the near-infrared band. Overall, dye-doped β-AG microplatelets with brilliant colors, high reflectivity and pearlescent luster are multifunctional composite materials, which possess broad application prospects in the fields of displays, inks and pearlescent pigments.