Synthesis and electroluminescence of poly(aryleneethynylene)s based on fluorene containing hole-transport units

A new series of light-emitting poly(aryleneethynylene)s (PAE) based on fluorene with sterically hindered substituents containing hole transport units such as tetraphenyldiaminobiphenyl, carbazole and thiophene and the non-planar unit binaphthyl were synthesized by a palladium-catalyzed coupling reaction. The introduction of hole transport moieties into the PAE main chain can improve the luminance properties of PAE type polymers. The electronic structures and photo- and electroluminescent (EL) properties of these polymers can be manipulated by simply varying the nature of the co-units in the polymeric chain. The spectral emission varies from greenish-blue to green or yellowish-green, depending on the composition of the copolymers. A single-layer light-emitting diode (LED) prepared from poly{[2,7-diethynyl-9,9-bis(2-ethylhexyl)fluorene]-alt-[N,N'-diphenyl-N,N'-bis(4-phenyl)-1,1'-biphenyl-4,4'-diamine]} (TPD-PFE) using an aluminium electrode emits green light (510 nm) with an EL external quantum efficiency of 0.007% and a brightness of 30 cd m(-2) at a bias voltage of 27 V and a current density of 420 mA cm(-2). An EL external quantum efficiency of 0.06% can be obtained from a blue-emitting double-layer LED with the structure of ITO/TPD-PFE/2-(2-hydroxyphenyl)pyridylberyllium/LiF/AlLi at a current density of 38 mA cm(-2).