This material is based upon work supported in part by the STC Program of the National Science Foundation under Agreement Number DMR-0120967. We also gratefully acknowledge Durel Corporation, the Office of Naval Research, NASA (through the University of Alabama at Huntsville), and the National Science Foundation for other financial support.
2,7-Bis(diarylamino)-9,9-dimethylfluorenes as Hole-Transport Materials for Organic Light-Emitting Diodes†
Article first published online: 17 NOV 2003
Copyright © 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Advanced Functional Materials
Volume 13, Issue 12, pages 967–973, December, 2003
How to Cite
Hreha, R.D., George, C.P., Haldi, A., Domercq, B., Malagoli, M., Barlow, S., Brédas, J.-L., Kippelen, B. and Marder, S.R. (2003), 2,7-Bis(diarylamino)-9,9-dimethylfluorenes as Hole-Transport Materials for Organic Light-Emitting Diodes. Adv. Funct. Mater., 13: 967–973. doi: 10.1002/adfm.200304464
- Issue published online: 17 NOV 2003
- Article first published online: 17 NOV 2003
- Manuscript Received: 10 JUL 2003
- Charge-carrier mobility;
- Hole-transporting materials;
- Light-emitting diodes, organic
2,7-Bis(p-methoxyphenyl-m′-tolylamino)-9,9-dimethylfluorene (1′), 2,7-bis(phenyl-m′-tolylamino)-9,9-dimethylfluorene (2′) and 2,7-bis(p-fluorophenyl-m′-tolylamino)-9,9-dimethylfluorene (3′) have been synthesized using the palladium-catalyzed reaction of the appropriate diarylamines with 2,7-dibromo-9,9-dimethylfluorene. These molecules have glass-transition temperatures 15–20 °C higher than those for their biphenyl-bridged analogues, and are 0.11–0.14 V more readily oxidized. Fluorescence spectra and fluorescence quantum yields for dimethylfluorene-bridged and biphenyl-bridged species are similar, but the peaks of the absorption spectra of 1′–3′ are considerably red-shifted relative to those of their biphenyl-bridged analogues. Time-of-flight hole mobilities of 1′–3′/polystyrene blends are in a similar range to those of the biphenyl-bridged analogues. Analysis according to the disorder formalism yields parameters rather similar to those for the biphenyl species, but with somewhat lower zero-field mobility values. Density functional theory (DFT) calculations suggest that the enforced planarization of the fluorene bridge leads to a slightly larger reorganization energy for the neutral/cation electron-exchange reaction than in the biphenyl-bridged system. Organic light-emitting diodes have been fabricated using 1′–3′/polystyrene blends as the hole-transport layer and tris(8-hydroxy quinoline)aluminium as the electron-transport layer and lumophore. Device performance shows a correlation with the ionization potential of the amine materials paralleling that seen in biphenyl-based systems, and fluorene species show similar performance to biphenyl species with comparable ionization potential.