Comparisons of the Efficiency of Excitation Energy Transfer by Singlet and Triplet Excitons in Carbazolyl-Containing Polymers
Luminescence spectra of poly-N-epoxypropylecarbazole (PEPC), poly-N-epoxypropyle-3,6- dichlorocarbazole (DClPEPC), and poly-N-epoxypropyle-3,6-dibromocarbazole (DBrPEPC) films, both pure and with the bis[2-(2′ -benzothienyl)-pyridinato-N,C3′ ](acetylacetonate) iridium (Btp2Ir(acac)) admixture, polystyrene (PS) films with the Btp2Ir(acac) admixture, and composite films of PEPC with the benzophenone and Btp2Ir(acac) admixtures have been studied. Those polymers are promising for their application in optoelectronic devices. It is found that, in the case of PEPC matrix, the excitation energy is transferred both via singlet excitons (through migration and long-range dipole-dipole interaction) and triplet ones (due to the migration and short-range electron exchange interaction). At the same time, in the films based on phosphorescent DBrPEPC, the energy transfer is only provided by triplet excitons. It is found that the quantum yield of the sensitized phosphorescence for Btp2Ir(acac) molecules in the carbazolyl-containing polymer matrix is lower than that under their direct excitation in the PS matrix. For the PEPC-based composite, this parameter is found to be three and five times higher than that for the DClPEPC and DBrPEPC matrices, respectively. The additional doping of the PEPC-based composite with benzophenone gave rise to the transformation of some singlet excitons into triplet ones and, as a result, to a reduction of the sensitized Btp2Ir(acac) phosphorescence intensity. A conclusion is drawn that, during the migration, some of both singlet and triplet excitons became localized in the tail energy states, and a certain fraction of triplet excitons is trapped by polymer oxidation products.
2. Y. Kawamura, S. Yanagida, S.R. Forrest. Energy transfer in polymer electrophosphorescent light emitting devices with single and multiple doped luminescent layers. J. Appl. Phys. 92, 87 (2002).
3. Y. Kawamura, K. Goushi, J. Brooks et al. 100% phosphorescence quantum efficiency of Ir(III) complexes in organic semiconductor films. Appl. Phys. Lett. 86, 071104 (2005).
4. B.C. Krummacher, V.-E. Choong, M.K. Mathai et al. Highly efficient white organic light-emitting diode. Appl. Phys. Lett. 88, 113506 (2006).
5. D.-H. Lee, J.S. Choi, H. Chae et al. Highly efficient phosphorescent polymer OLEDs fabricated by screen printing. Displays 29, 436 (2008).
6. H.A. Al-Attar, A.P. Monkman. Solution processed multilayer polymer light-emitting diodes based on different molecular weight host. J. Appl. Phys. 109, 74516 (2011).
7. Sung Il Ahna, Wan Kyu Kim, Si Hong Ryu, Kuk Joo Kim, Seong Eui Lee, Sung-Hoon Kim, Jung-Chul Park, Kyung Cheol Choi. OLED with a controlled molecular weight of the PVK (poly(9-vinylcarbazole)) formed by a reactive inkjet process. Org. Electron. 13, 980 (2012).
8. J. Birnstock, J. Blassing, A. Hunze et al. Screen-printed passive matrix displays based on light-emitting polymers. Appl. Phys. Lett. 78, 3905 (2001).
9. C.D. Muller, A. Falcou, N. Reckefuss et al. Multi-colour organic light-emitting displays by solution processing. Nature 421, 829 (2003).
10. C.W. Tang, S.A. VanSlyke. Organic electroluminescent diodes. Appl. Phys. Lett. 51, 913 (1987).
11. P.A. Lane, L.C. Palilis, D.F. O'Brien et al. Origin of electrophosphorescence from a doped polymer light emitting diode. Phys. Rev. B 63, 235206 (2001).
12. S. Blumstengel, F. Meinardi, R. Tubino. Long-range energy transfer of singlet and triplet excitations in dyedoped tris(phenylquinoxaline). J. Chem. Phys. 115, 3249 (2001).
13. H. Xu, R. Chen, Q. Sun et al. Recent progress in metalorganic complexes for optoelectronic applications. Chem. Soc. Rev. 43, 3259 (2014).
14. A.V. Vannikov, A.D. Grishina. Photochemistry of Polymeric Donor-Acceptor Complexes (Nauka, 1984) (in Russian).
15. Yu.A. Skryshevskii. Photostability of molecules of aromatic amines in a polymeric matrix. J. Appl. Spectrosc. 69, 726 (2002).
16. W.J. Finkenzeller, M.E. Thompson, H.Yersin. Phosphorescence dynamics and spin-lattice relaxation of the OLED emitter Ir(btp)2(acac). Chem. Phys. Lett. 444, 273 (2007).
17. Y. Kawamura, J. Brooks, J.J. Brown et al. Intermolecular interaction and a concentration-quenching mechanism of phosphorescent Ir(III) complexes in a solid film. Phys. Rev. Lett. 96, 017404 (2006).
18. Yu.P. Piryatinskii, V.N. Yashchuk, Yu.A. Cherkasov et al. Luminescence of poly-N-epoxypropylcarbazole. Zh. Prikl. Spektrosk. 53, 41 (1990) (in Russian).
19. I.S. Gorban', T.P. Volkova, A.Ya. Kalnitskii, V.N. Yashchuk. On the nature of structureless phosphorescenceof vinyl aromatic polymers. Ukr. Fiz. Zh. 29, 1267 (1984) (in Russian).
20. Yu.A. Skryshevskii. Electronic excitation energy transfer in poly-N-epoxypropyl-3,6-dibromocarbazole. Phys. Solid State 52, 1308 (2010).
21. S.P. McGlynn, T. Azumi, M. Kinoshita, Molecular Spectroscopy of the Triplet State (Prentice-Hall, 1969).
22. S.M. Bonesi, R. Erra-Balsells. Electronic spectroscopy of N- and C-substituted chlorocarbazoles in homogeneous media and in solid matrix. J. Luminesc. 97, 83 (2002).
23. Yu.A. Skryshevski. Energy transfer by singlet and triplet excitons in carbazole-containing polymers. J. Appl. Spectrosc. 79, 559 (2012).
24. M. Pope, C.E. Svenberg, Electronic Processes in Organic Crystals (Oxford Univ. Press, 1982).
25. H. Bassler. Excitons in conjugated polymers. In Primary Photoexcitations in Conjugated Polymers: Molecular Exciton versus Semiconductor Band Model. Edited by N.S. Sariciftci (World Scientific, 1997).
26. E.A. Akimova, A.V. Stronskii, A.P. Payuk et al. Recording of holografic diffraction gratings on carbazole-containing polymer thin films. Optoelektron. Poluprovodn. Tekhn. 49, 31 (2014) (in Russian).
27. H. Bassler. Exciton and charge carrier transport in random organic solids. In Disorder Effects on Relaxational Processes, edited by R. Richert, A. Blumen (Springer, 1994).
28. N.D. Zhevandrov, T.V. Ilyinykh. Study of the ratio of the energy transfer efficiencies for triplet and singlet levels in impure molecular crystals. Izv. Akad. Nauk SSSR Ser. Fiz. 42, 334 (1978) (in Russian).
29. J. Jortner, S.A. Rice, J.L. Katz, S. Choi. Triplet excitons in crystals of aromatic molecules. J. Chem. Phys. 42, 309 (1965).
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