An initial solvent screening technique using 23 kinds of common organic solvents was utilized to engineer the polymorphism and crystallinity of the solids of organic electroluminescent molecules of tris(8-hydroxyquinoline) aluminum(III) (Alq3). Pure Alq3 recrystallized from N,N -dimethyl formamide (DMF) by temperature cooling from 60 to 25 °C gave rodlike, semicrystalline solid materials with traces of δ-form having a sublimation point of only around 200 ± 5 °C. The sublimation point depression of source materials could reduce the current evaporation temperature of organic light-emitting diodes (OLEDs) drastically. In addition, three new solvates of Alq3(C 6 H 5 NO 2 ) 1/5 (H 2 O) 6, Alq3(CHCl 3 ) 1/4, and Alq3(C 4 H 8 O 2 ) 1/2 were discovered from the initial solvent screening.
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Lee et al. (2007) studied this question.