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Long-range resonantly enhanced triplet formation in luminescent polymers doped with iridium complexes

Nature Materials volume 5, pages 463–466 (2006)Cite this article

Abstract

The current drive to produce cheap, flexible plastic displays1 has led to rapid improvements in device efficiency. Inclusion of highly phosphorescent heavy-metal organic complexes as dopants ensures that both singlet and triplet excitations formed on charge recombination can be used efficiently to emit light2. However, the inclusion of these dopants affects the photophysics of the host in a surprising way, generating a ten- to twenty- fold instantaneous increase in the number of host triplet states, independent of host triplet energy, quenching up to 95% of all singlet states. Once created however, these triplets are only weakly quenched by the same mechanism. We ascribe this to a resonant, remote intermolecular heavy-atom effect that greatly increases the inter-system crossing rate of the host polymer3 arising through the strong overlap of the delocalized π orbitals of the host and ligands. This mechanism competes effectively with Förster energy transfer, and operates over large distances.

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Figure 1: Absorption, emission and phosphorescence spectra.
Figure 2: Double logarithmical presentation of the time-dependent PSF triplet–triplet absorption signal measured at 780 nm (1.6 eV) after pulsed excitation of the host polymer at 355 nm (3.5 eV).
Figure 3: Time-resolved transient triplet absorption curves of the copolymer triplet density with (red) and without (black) 8% Ir-SC4 guest loading.
Figure 4: Time-resolved photoinduced absorption signals of the PSF host polymer measured at 780 nm (1.6 eV).

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Acknowledgements

The authors wish to thank Covion (now Merck) and B. M. W. Langevelt for supplying materials, H. Burrows for helpful discussions and CENAMPS and ONE North East for financial support.

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  1. Department of Physics, O.E.M Research Group, University of Durham, Durham, DH1 3LE, UK

    Carsten Rothe, Simon King & Andrew Monkman

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Correspondence to Andrew Monkman.

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Rothe, C., King, S. & Monkman, A. Long-range resonantly enhanced triplet formation in luminescent polymers doped with iridium complexes. Nature Mater 5, 463–466 (2006). https://doi.org/10.1038/nmat1630

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