New 3D-stereoconfigurated cis-tris(fluorenylphenylamino)-benzene with large steric hindrance to minimize π–π stacking in thin-film devices

Highly fluorescent trans- and cis-tris(fluorenylphenylamino)benzene stereo-isomeric derivatives, trans- and cis-tris(DPAF-C₉), respectively, were designed and synthesized to minimize facile planar fluorene ring stacking in the solid state during thin-film device fabrications. Resulting tris-cup cis- and tris-chair trans-conformers were hypothesized to be capable of reducing direct packing contact of light-harvesting fluorene moieties from each other that should reduce the aggregation-related self-quenching effect derived from the π–π stacking packing arrangement. By the fact of closely matching photophysical characteristics of them to those of poly(N-vinylcarbazole) (PVK), we applied the former conformer as the secondary blue hole-transporting material in the study of its electroluminescence properties, using a tricomponent system of PVK‒cis-tris(DPAF-C₉)‒tris(2-phenylpyridine)iridium (III) [Ir(ppy)₃], as an example. Accordingly, several prototype single-layered or multilayered devices were fabricated with their electroluminescence and external quantum efficiency demonstrated. These analogous 3D-stereoconformers can also be used in other fluorescence-related thin-film applications.