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Activating efficient phosphorescence from purely organic materials by crystal design

An Addendum to this article was published on 15 March 2011

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Abstract

Phosphorescence is among the many functional features that, in practice, divide pure organic compounds from organometallics and inorganics. Considered to be practically non-phosphorescent, purely organic compounds (metal-free) are very rarely explored as emitters in phosphor applications, despite the emerging demand in this field. To defy this paradigm, we describe novel design principles to create purely organic materials demonstrating phosphorescence that can be turned on by incorporating halogen bonding into their crystals. By designing chromophores to contain triplet-producing aromatic aldehydes and triplet-promoting bromine, crystal-state halogen bonding can be made to direct the heavy atom effect to produce surprisingly efficient solid-state phosphorescence. When this chromophore is diluted into the crystal of a bi-halogenated, non-carbonyl analogue, ambient phosphorescent quantum yields reach 55%. Here, using this design, a series of pure organic phosphors are colour-tuned to emit blue, green, yellow and orange. From this initial discovery, a directed heavy atom design principle is demonstrated that will allow for the development of bright and practical purely organic phosphors.

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Figure 1: Directed heavy atom organic phosphorescence and its design principle.
Figure 2: Photophysical properties of Br6A (1).
Figure 3: Dependence of emission on crystal growth.
Figure 4: Photophysical properties of mixed crystals of Br6A (1) and Br6 (2).
Figure 5: Photophysical properties of colour-tuned aromatic aldehydes.

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  • 15 March 2011

    After the publication of this Article the authors found a further relevant paper that they would like to cite. The paper reports crystallization-induced rotational restriction of benzophenone derivatives and ensuing phosphorescence enhancement: Yuan, W. Z. et al. Crystallization-induced phosphorescence of pure organic luminogens at room temperature. J. Phys. Chem. C 114, 6090–6099 (2010).

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Acknowledgements

The authors thank J.W. Kampf, S. Lin and K. Noon for critical services. The initial discovery of the presented phosphorescence was made while we were conducting a project supported by a National Science Foundation (NSF) CAREER Award (DMR 0644864). This work was partly supported by a WCU (World Class University) program through National Research Foundation of Korea funded by the Ministry of Education, Science and Technology (R31-2008-000-10075-0).

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Authors

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O.B. synthesized all materials and crystals, made all photophysical measurements and analyses presented, and wrote the paper. K.L. made the initial discovery of phosphorescence. H.-J.K. assisted in early optical analyses. K.Y.L. conducted high-performance liquid chromatography to identify the aldehyde structure. J.K designed and supervised the research and oversaw the writing of the paper.

Corresponding author

Correspondence to Jinsang Kim.

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The authors declare no competing financial interests.

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Supplementary information (PDF 929 kb)

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Supplementary movie S2 (MPG 27160 kb)

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Crystallographic data for compound 1 (Br6A) (CIF 13 kb)

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Crystallographic data for compound 2 (Br6) (CIF 10 kb)

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Bolton, O., Lee, K., Kim, HJ. et al. Activating efficient phosphorescence from purely organic materials by crystal design. Nature Chem 3, 205–210 (2011). https://doi.org/10.1038/nchem.984

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