Phase Diagrams of Anthracene Derivatives in Pyridinium Ionic Liquids

Crystal engineering for single crystallization of pi-conjugated molecules has attracted much attention because of their electronic, photonic, and mechanical properties. However, reproducibility is a problem in conventional printing techniques because control of solvent evaporation is difficult. We investigated the phase diagrams of two anthracene derivatives in synthesized ionic liquids for non-volatile crystal engineering to determine the critical points for nucleation and crystal growth. Anthracene and 9,10-dibromoanthracene were used as representative pi-conjugated molecules that form crystal structures with different packing types. Ionic liquids with an alkylpyridinium cation and bis(fluorosulfonyl)amide were good solvents for the anthracene derivatives from ca. 0 degrees C to 200 degrees C. The solubilities (critical points for crystal growth) of the anthracene derivatives in the ionic liquids reached the 100 mM level, which is similar to those in organic solvents. Ionic liquids with phenyl and octyl groups tended to show high-temperature dependence (a high dissolution entropy) with 9,10-dibromoanthracene. The precipitation temperature (critical point for crystal nucleation) at each 9,10-dibromoanthracene concentration was lower than the dissolution temperature. The differences between the dissolution and precipitation temperatures (supersaturated region) in the ionic liquids were greater than those in an organic solvent. For the development of non-volatile crystal engineering, phase diagrams of anthracene and 9,10-dibromoanthracene in ionic liquids are prepared to know the critical points for nucleation and crystal growth. The ionic liquids consisting of pyridinium cation and bis(fluorosulfonyl)amide anion are synthesized. The dissolution enthalpy and entropy are calculated from van ' t Hoff's equation. image