Highly phenyl-substituted polyfluorenes for light-emitting diodes

Abstract

Highyl phenyl-substituted polyfluorenes were synthesized by Diels-Alder polymerization of 2,7-diethynyl-9,9-di-n-hexyltluorene and the corresponding bis(cyclopentadienones). The resulting polymers with high molecular weights were shown to be good solubility in chloroform, stable up to 400 degreesC, highly luminescent, and also easily cast to give good thin-films. The UV-visible and photoluminescence (PL) spectra of the polymer I showed maximum peak at 316 nm and at 450 nm, respectively. The single-layered light-emitting diode of an Al/polymer I or polymer II/PVK (2:8) blend/ITO glass exhibited a threshold voltage of 8 V from the I-V curve. The electroluminescence (EL) devices based on polymer 1 and polymer 11 gave the emissive peaks at 436 nm and 404 nm, respectively.