Published on Web 06/06/2003
Phosphorescence Quenching by Conjugated Polymers Madhusoodhanan Sudhakar, Peter I. Djurovich, Thieo E. Hogen-Esch, and Mark E. Thompson* Department of Chemistry, UniVersity of Southern California, Los Angeles, California 90089 Received January 24, 2003; E-mail:
[email protected] Efficient organic light-emitting diodes (OLEDs) have been fabricated with low-molecular weight materials.1 Hole-electron recombination in these OLEDs leads to the formation of both singlet and triplet excited states (excitons) within the molecular thin film.2 For most compounds, only the singlet state is emissive, leading to a significant limitation in the OLED efficiency. Incorporation of phosphorescent compounds into the OLED gives a substantial improvement in device efficiency, since both the singlet and triplet excitons are trapped at the phosphor. This approach has led to OLEDs with external quantum efficiencies (photon/electron) of roughly 20% which correspond to internal efficiencies of nearly 100%.3 Conjugated polymers have also been used to prepare OLEDs, e.g. poly(phenylenevinylenes),4a polyfluorenes,4b and poly(pphenylenes).4c While these devices can have good power efficiencies (lum/W or Wopt/Welect), the polymer-based OLEDs tend to give external quantum efficiencies of less than 5%. Several groups have attempted to increase the quantum efficiencies of conjugated polymer-based OLEDs by incorporating phosphorescent dopants.5 However, while the efficiencies of conjugated polymer OLEDs are improved by phosphor doping, values are still markedly lower than those of small-molecule-based devices (10% external) polymer-based phosphorescent OLEDs. Acknowledgment. We thank The Universal Display Corporation (M.E.T.) and the NSF-DMR (T.H.E.) for financial support of this work. Supporting Information Available: Phosphorescence spectra from the phosphors, synthesis and characterization of F3, electrochemical properties of the compounds, and data for the Stern-Volmer analysis (PDF). This material is available via the Internet at http://pubs.acs.org. References (1) (a) Mitscheke, U.; Bauerle, P. J. Mater. Chem. 2000, 10, 1471-1507. (b) Tsutsui, T.; Fujita, K. AdV. Mater. 2002, 14, 949-952. (2) Baldo, M. A.; O’Brien, D. F.; Thompson, M. E.; Forrest, S. R. Phys. ReV. B 1999, 60, 14422-14428. (3) (a) Adachi, C.; Baldo, M. A.; Thompson, M. E.; Forrest, S. R. J. Appl. Phys. 2001, 90, 5048-5051. (b) Ikai, M.; Tokito, S.; Sakamoto, Y.; Suzuki, T.; Taga, Y. Appl. Phys. Lett. 2001, 79, 156-158. (4) (a) Friend, R. H.; Gymer, R. W.; Holmes, A. B.; Burroughes, J. H.; Marks, R. N.; Taliani, C.; Bradley, D. D. C.; Dos Santos, D. A.; Bredas, J. L.; Salaneck, W. R. Nature 1999, 397, 121-128. (b) Millard, I. S. Synth. Met. 2000, 111-112, 119-123. (c) Wohlegenannt, M.; Tandon, K.; Mazumdar, S.; Ramashesha, S.; Vardeny, Z. V. Nature 2001, 409, 494497. (5) (a) Gross, M.; Nuller, D. C.; Nothofer, H.-G.; Scherf, U.; Neher, D.; Brauchle, C.; Meerholz, K. Nature 2000, 405, 661-665. (b) Chen, X.; Liao, J.-L.; Liang, Y.; Ahmed, M. O.; Tseng, H.-E.; Chen, S.-C. J. Am. Chem. Soc. 2003, 125, 636-637. (c) Higgins, R. W. T.; Monkman, A. P.; Nothofer, H.-G.; Scherf, U. J. Appl. Phys. 2002, 91, 99-105. (d) Zhu, W.; Liu, C.; Su, L.; Yang, W.; Yuan, M.; Cao, Y. J. Mater. Chem. 2003, 13, 50-55. (e) Chen, F.-C.; Yang, Y.; Thompson, M. E.; Kido, J. Appl. Phys. Lett. 2002, 80, 2308-2310. (6) (a) Yang, M.-J.; Tsutsui, T. Jpn. J. Appl. Phys., Part 2 2000, 39, L828L829. (b) Kawamura, Y.; Yanagida, S.; Forrest, S. R. J. Appl. Phys. 2002, 92, 87-93. (7) Vaeth, K. M.; Tang, C. W. J. Appl. Phys. 2002, 92, 3447-3453. (8) Lamansky, S.; Djurovich, P.; Murphy, D.; Abdel-Razzaq, F.; Lee, H.-E.; Adachi, C.; Burrows, P. E.; Forrest, S. R.; Thompson, M. E. J. Am. Chem. Soc. 2001, 123, 4304-4312. (9) Hertel, D.; Romanovskii, Y. V.; Schweitzer, B.; Scherf, U.; Ba¨ssler, H. Macromol. Symp. 2001, 175, 141-150. (10) Refer to the Supporting Information. (11) Turro, N. J. Modern Molecular Photochemistry; The Benjamin/Cummings Publishing Co., Inc.; Menlo Park, California, 1978. (12) Noh, Y.-Y.; Lee, C.-L.; Kim, J.-J.; Yase, K.; J. Chem. Phys. 2003, 118, 2853-2864.
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