Starting with the groundbreaking work of Forrest et al. in 1998 [1], great efforts have been made in the development of Phosphorescent Organic Light Emitting Diodes (PHOLEDs), due to their high internal quantum efficiency. Since then 4,4’-bis(9-carbazolyl)biphenyl (CBP) has been widely used as host material for various dopants in PHOLEDs [2]. However, CBP exhibits some major drawbacks as low glass transition temperature (62 °C) and low triplet energy (2.56 eV) resulting in devices with short lifetime and inefficient energy transfer to high energy (ET) blue guest emitters [2].
Recently we introduced the fully planar indolo[3,2,1-jk]carbazole (ICz) moiety as building block for high ET host materials [3]. Our recent research focused on the incorporation of the ICz motive to the CBP scaffold by planarization of the phenylcarbazole moieties in order to improve the above mentioned molecular properties of CBP.
The synthesis and detailed characterization of three novel planarized CBP derivatives as well as application in prototype PHOLED devices will be presented in this contribution.
[1] M. A. Baldo, D. F. O'Brien, Y. You, A. Shoustikov, S. Sibley, M. E. Thompson, S. R. Forrest, Nature 1998, 395, 151-154. [2] Y. Tao, C. Yang, J. Qin, Chemical Society Reviews 2011, 40, 2943-2970. [3] P. Kautny, D. Lumpi, Y. Wang, A. Tissot, J. Bintinger, E. Horkel, B. Stöger, C. Hametner, H. Hagemann, D. Ma, J. Fröhlich, J Mater Chem C 2014, 2, 2069-2081.