Electron Transport Materials for Organic Light-Emitting Diodes: Understanding the Crystal and Molecular Stability of the Tris(8-hydroxyquinolines) of Al, Ga, and In

摘要

An experimental and theoretical study on the phase and molecular stability of Mq3 (M = Al, Ga, and In; q = 8-hydroxyquinoline) is presented. The results suggest that the energy difference between the meridional and facial isomers of Mq3 shall be significantly lower than previously though and provide an explanation for the reported mer—fac solid—solid transition. The first accurate vapor pressure measurements for Alq3, Gaq3, and Inq3 are presented, which are of great relevance for the manufacturing of thin films by vacuum deposition. Phase transition thermodynamics indicates higher cohesive energies of the mer-isomers and an entropic differentiation that can be associated with the different molecular symmetry of the tner- and fac-isomers.