Electroactive polymers containing pendant harmane, phenoxazine or carbazole rings as host materials for OLEDs E. Zaleckas a , R. Griniene a , B. Stulpinaite a , J.V. Grazulevicius a , L. Liu b , Z. Xie b , E. Schab-Balcerzak c, d , E. Kamarauskas e , B. Zhang b, * , S. Grigalevicius a, * a Department of Polymer Chemistry and Technology, Kaunas University of Technology, Radvilenu plentas 19, LT50254 Kaunas, Lithuania b State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 130022 Changchun, China c Institute of Chemistry, University of Silesia, 9 Szkolna Street, 40-006 Katowice, Poland d Centre of Polymer and Carbon Materials, Polish Academy of Sciences, 34 M. Curie-Sklodowska Street, 41-819 Zabrze, Poland e Department of Solid State Electronics, Vilnius University, Sauletekio aleja 9, LT10222 Vilnius, Lithuania article info Article history: Received 5 March 2014 Received in revised form 19 April 2014 Accepted 25 April 2014 Available online 6 May 2014 Keywords: Vinyl monomer Electroactive material Polystyrene Ionization potential Host Light emitting diode abstract Polystyrenes containing electronically isolated harmane, phenoxazine or carbazole rings were synthe- sized and characterized by NMR spectroscopy, elemental analysis and gel permeation chromatography. The new polymers represent amorphous materials of high thermal stability with glass-transition tem- peratures of 139e179  C. The electron photoemission spectra of layers of the synthesized polymers showed ionization potentials of about 5.6e6.0 eV. The polymers were tested as host materials in phosphorescent green OLEDs with bis(2-phenylpyridine)(acetylacetonato)iridium(III) as the guest. The device based on polymer containing phenoxazine fragments exhibited the best overall performance with a turn-on voltage of 2.8 V, maximum photometric efficiency of about 17 cd/A and maximum brightness of 2920 cd/m 2 . Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Improvements in the performance of organic light emitting di- odes (OLEDs) over the past decade have resulted in commercially available products. The efficiencies of OLED devices have advanced rapidly in recent years because of the development of efficient emitters [1e5] as well as efficient phosphorescent guest molecules containing transition metals [6e8]. In the phosphorescent devices, to reduce quenching associated with relatively long excited-state lifetimes of triplet emitters and tripletetriplet annihilation, the emitters are normally used as emitting guests in a host material, and thus suitable host materials are of equal importance for electro-phosphorescent OLEDs. The triplet level of the hosts should be larger than that of the triplet emitter to prevent energy transfer from the guest back to the host and to confine effectively triplet excitons to the guest molecules [9e11]. It was reported earlier that carbazole- and indole-based derivatives demonstrate rather large triplet energies and are potential host materials for electro-phosphorescent devices [12e14]. Here, we report on new electroactive polymers containing electronically isolated pendant harmane, phenoxazine or carbazole rings. The fragments of aro- matic heterocyclic compounds are attached to long and neural alkyl chains of the macromolecules and have not an electronic interac- tion. The polymers should have high triplet energy and are suitable as polymeric hosts for large area OLED devices. 2. Experimental 2.1. Instrumentation 1 H NMR spectra were recorded using a Varian Unity Inova (300 MHz) instrument. Mass spectra were obtained on a Waters ZQ 2000 spectrometer. UV spectra were measured with a Spectronic GenesysÔ 8 spectrometer. Fluorescence (FL) spectra were recorded with a Hitachi MPF-4 spectrometer. The molecular weights of polymers were determined by a gel permeation chromatography (GPC) system including GMH HR -M * Corresponding authors. E-mail addresses: bhzhang512@ciac.ac.cn (B. Zhang), saulius.grigalevicius@ktu.lt (S. Grigalevicius). Contents lists available at ScienceDirect Dyes and Pigments journal homepage: www.elsevier.com/locate/dyepig http://dx.doi.org/10.1016/j.dyepig.2014.04.034 0143-7208/Ó 2014 Elsevier Ltd. All rights reserved. Dyes and Pigments 108 (2014) 121e125