Open micro-combinatorial analysis systems of crystal growth critical points of a π-conjugated molecule in ionic liquid nanoliter droplets.

Crystal engineering methodologies based on reproducible and high-throughput fabrication of high-quality single crystals have attracted much attention. Crystal formation and growth are governed by crystal growth theory. The driving force of crystallization is systematically represented with phase diagrams. However, constructing phase diagrams usually requires relatively large quantities of samples (milligrams to grams) and substantial time (weeks to months) to evaluate many conditions. Therefore, an easy and quick methodology to obtain phase diagrams, revealing critical conditions for valuable samples, is required. Here, we proposed a new method to obtain phase diagrams based on nanoliter droplet arrays of nonvolatile ionic liquids prepared by inkjet printing. Anthracene derivatives and 1-octyl-4-methylpyridinium derivatives were used as the solute and solvent, respectively. Optimization of ejection conditions, such as applied voltage, frequency, pulse width, and head temperature, enabled the formation of a 0.5 nL droplet per ejection. Inkjet printing under these conditions formed nanodroplet arrays on substrates at a droplet-patterned density of