3D Monodisperse Oligofluorenes with Non‐Conjugated Triphenylamine‐Based Cores: Synthesis and Optoelectronic Properties

Abstract

AbstractTwo 3D monodisperse oligofluorenes with non‐conjugated triphenylamine‐based cores have been synthesized byFriedel–Crafts copolycondensation reaction. The oligomers, PF3‐TPA and PF3‐TPA3, consist of three fluorene pentamer arms that are connected non‐conjugately through a triphenylamine (TPA) and 1,3,5‐tris(triphenylamino)benzene core (TPA3), respectively, at the 9‐position of the central fluorene of the pentafluorene arms. The coplanar structures ofthe cores and the linkages at the centre of the pentafluorene arms produced a 3D structure of oligomers. This specific structure efficiently retarded the crystallization tendencies of the pentafluorene arms and gave the materials completely amorphous morphological structures. Both oligomers emit deep‐blue fluorescence with high efficiencies in thin films (φpl–film = 67 % for PF3‐TPA3 and 86 % for PF3‐TPA). The introduction of triphenylamine units into the core promoted the hole‐injection ability while not obviously scarificing the electron‐injection ability of the oligomers. The multi‐layer devices ITO/PEDOT‐PSS/PF3‐TPA3 and PF3‐TPA/TPBI/LiF/Al were fabricated to investigate the electroluminescence (EL) properties of the two oligomers. Both oligomers showed a low turn‐on voltage of 4 V. The luminances reached 1946 cd/m2 at 7.5 V in the PF3‐TPA3 device and 1055 cd/m2 at 8 V in the PF3‐TPA device. The EL efficiencies at this luminance were 1.63 and 1.57 cd/A, respectively.