Pure color and stable blue-light emission-alternating copolymer based on fluorene and dialkoxynaphthalene

Abstract

A new blue-light emitting polymer that alternates between fluorene and alkoxynaphthalene structure has been developed. The fluorene and naphthalene units were highly distorted with an angle of 76.22 degrees according to theoretical calculations. The obtained polymer has a weight average molecular weight of 273,800 with a polydispersity index of 2.35, good solubility and high thermal stability with a T-g of 176 degrees C. The film photoluminescence (PL) spectrum (405 nm) is consistent with that of solution and the PL spectra of the polymer did not show any peak in the long wavelength region even after annealing for 24 h at 100 degrees C. The double-layered device with an ITO/PEDOT/polymer/LiF/Al structure has a turn-on voltage of about 5.4 V, maximum brightness of 110 cd/m(2) and an electroluminescent efficiency of 0.09 cd/A. The OLED generates pure blue EL emission (lambda(max) = 405 nm) with excellent CIE coordinates (x = 0.15, y = 0.10) as well as stable blue EL emission that is not altered by voltage increase. (C) 2008 Elsevier Ltd. All rights reserved.