Unidirectional growth of organic single crystals of naphthalene, anthracene and pyrene by isothermal expansion of supercritical CO.

Unidirectional single crystals without grain boundaries are highly important in optoelectronic applications. Conventional methods to obtain such crystals involve organic solvents or seed crystals, which have numerous drawbacks. We present here a supercritical CO-mediated method of the single crystal formation of naphthalene, anthracene and pyrene on the (001) plane without using seed crystals. Single dominant peaks in powder XRD (PXRD) with low full width at half maxima (FWHM) are described. The dependency of crystal size on the rate of depressurization was measured by precise and isothermal expansion of scCO solutions. The experimental setup is illustrated for continuous preparation without emission of CO or discharge of material into the environment. The materials are shown to be fully converted into crystals indicating a rapid, scalable and environmentally benign process of single crystal formation with practically nil E factor.