Synthesis and Photoluminescent Properties of Geometrically Hindered cis-Tris(diphenylaminofluorene) as Precursors to Light-Emitting Devices

A novel highly luminescent tris-fluorenyl ring-interconnected chromophore tris(DPAF-C(9)) was synthesized using a C(3) symmetrical triaminobenzene core as the synthon. This structure bears three light-harvesting 2-diphenylamino-9,9-dialkylfluorenyl (DPAF) ring moieties with each attached by two branched 3',5',5'-trimethylhexyl (C(9)) arms. A major stereoisomer was chromatographically isolated and characterized to possess a 3D structural configuration of cis-conformer in a cup-form. Molecular calculation at B3LYP/6-31G* level revealed the unexpected stability of this cis-cup-conformer of tris(DPAF-C(9)) better than that of the stereoisomer in a propeller-form and the trans-conformer. The structural geometry is proposed to be capable of minimizing the aggregation related self-quenching effect in the condensed phase. Fluorescence emission wavelength of tris(DPAF-C(9)) was found to be in a close range to that of PVK that led to its potential uses as the secondary blue hole-transporting material for enhancing the device property toward the modulation of PLED performance.