Excimer emission of anthracene, perylene, coronene and pyrene microcrystals dispersed in water

Microcrystals of aromatic hydrocarbons such as perylene, pyrene, coronene and anthracene were prepared as an aqueous suspended solution by a stratificational sublimation with water onto a substrate cooled by liquid nitrogen. Aqueous solutions of microcrystals showed anomalous fluorescence spectra different from those of bulk crystals; coronene exhibited monomer and broad excimer emissions, while pyrene showed a red-shifted excimer band, and anthracene or perylene showed both excimer and monomer bands. The relative intensities of two bands were varied systematically with the size of the microcrystals. The dual emissions are explained by assuming two emission centers, one is in the mid and another is on the periphery of microcrystals. The diffusion lengths of exciton were estimated for anthracene and perylene microcrystals from the intensity ratio of two emission bands.