Soluble Electroluminescent Poly(phenylene vinylene)s with Balanced Electron- and Hole Injections

Abstract

We report a new route for the design of efficient soluble electroluminescent PPV-based copolymers bearing electron-deficient oxadiazole (OXD) moieties on side chains. The introduction of OXD through a long alkylene spacer with PPV backbone provides a molecular dispersion of OXD in the film; both the side chain OXD and the main chain PPV do retain their own electron-transport and emissive properties, respectively. The use of phenylene vinylene derivatives with asymmetric and branched substituents and a long spacer provides solubility for ease of device fabrication as well as amorphous structure to allow a well-mixing of OXD groups with the main chains. By properly adjusting the OXD content through copolymerization, we can tailor the chemical structure of electroluminescent material to give a balance of hole- and electron injections for various metal cathodes, such that the quantum efficiency is significantly improved and the turn-on voltage is reduced for the devices with aluminum and calcium. For the device with calcium fabricated in open air, a maximum brightness of 15000 cd/m(2) at 15 V/100 nm and a maximum luminance efficiency of 2.27 cd/A can be obtained, respectively, about 30 times brighter and 9.4 times more efficient than those with the corresponding homopolymer, poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV). The use of physical blends to simulate the copolymers provides no significant improvement, since phase-separation structures appear, causing an inefficient utilization of OXD and sometimes voltage-dependent emission spectra. The present route permits a fabrication of single layer PLED with high brightness, high efficiency, and low turn-on voltage.

Cyclic Polymers with Pendent Carbazole Units: Enhanced Fluorescence and Redox Behavior

“…It was observed that DI p vaules (the difference between anodic I pa and cathodic peak electric current I pc ) for the cyclic PVBCZ were larger than those of corresponding linear precursor, suggesting that the cyclic PVBCZ could have an efficient charge-transport site. [21] The electrochemical properties of cyclic PVBCZ is now being explored in detail.…”

Blue light‐emitting poly(p‐phenylenevinylene) derivative with oxadiazole and carbazole pendant groups

“…This synthetic route is slightly different from the one that has been reported. 24 Specifically, in the present case, 4-hydroxybenzoic acid, the starting material, reacted with acetylchloride to afford the corresponding acetoxy derivative. Following the construction of the oxadiazole ring, the acetoxy group was hydrolyzed by acid catalyzed hydrolysis.…”

Synthesis and phosphorescent properties of the copolymers of N-vinylcarbazole, methyl methacrylate and iridium complex

“…The onset oxidation potential (E onset (ox)) is 1.48 V and onset reduction potential (E onset (red)) is −1.20 V. It is suggested that the copolymer containing iridium has better electron injection and transporting properties due to the incorporation of charged Ir complex into the copolymer. The HOMO and LUMO energy levels of the polymer materials can be calculated from the E onset (ox) and E onset (red), based on the reference energy level of ferrocene (4.8 eV below the vacuum level) [20,21] 2 Cl/PVK(1.0) is estimated to be about 5.88 eV, and LUMO level to be about 3.2 eV. As a result, it may be a good candidate as a electrophosphorescent material for application in PLED.…”