Preparation of New Conjugated Polymers for Application in Light Emitting Diodes

Abstract

PLEDs based on traditional fluorescent materials have generally restricted external quantum efficiencies (EQEs) around 5% because of spin statistic rules, which greatly limit their comprehensive application. Furthermore, by simultaneously using singlet and triplet excitons by intersystem crossing (ISC), the internal quantum efficiency (IQE) of PLED devices that include organometallic phosphors is almost 100%. However, the rare and expensive noble metals, such as Ir or Pt, are common components in heavy-metal complexed phosphorescent materials. Because of the rarity of these minerals, the devices produced are consequently costly, thus driving the search for less expensive alternatives. Thermally activated delayed fluorescence (TADF) OLEDs are potential options, as the IQE is theoretically able to collect both singlet and triplet excitons. The pure organic materials required for the reverse intersystem crossing (RISC) are comparatively cheap. Due to its high triplet energy and good hole-transporting property, this study proposes TADF polymers with backbones comprising carbazole and fluorene units. We grafted 10-(4-(5- phenyl-1,3,4-oxadiazol-2-yl)phenyl)-10H phenoxazine (TRZ-PXZ) trough alkyl side chains onto the main-chain of polymers through Suzuki or Sonogashira copolycondensation reactions of different substituted monomers. In chapter III, we introduce the preparation of an AB2 hyperbranched polymer using 3,4-(3,6-diacetoxy-9H-carbazol-9-yl)benzoic acid in the presence of a constant molar ratio of 4-nitrophenyl acetate as core. The chemical purity of all 1 13 the compounds was investigated further through the use of H-NMR, C-NMR, elemental analysis and mass spectrometry techniques. To establish the thermal properties, optical and electrochemical properties, thermal gravimetric analysis, ultraviolet-visible spectroscopy (UV- vis), and cyclic voltammetry (CV) was used to examine the resulting conjugated polymers.