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Insights into energy transfer pathways between the exciplex host and fluorescent guest: attaining highly efficient 710 nm electroluminescence

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Abstract

Energy transfer between the exciplex host and fluorescent guest is a demanding process for attaining high-performance organic light-emitting diodes (OLEDs), particularly in the near-infrared (NIR) region, and insight into the dynamics of energy transfer has been elusive. In this study, new deep-red/NIR chromophores, NOz-TPA and NOz-t-TPA where NOz and TPA denote naphthobisoxadiazole and triphenylamine, respectively, have been developed with an electron donor–acceptor–donor (D–A–D) configuration. The optimized 1 wt% doped films for NOz-TPA and NOz-t-TPA blended with the Tris-PCz:CN-T2T (1 : 1 in molar ratio) exciplex host showed similar deep red/NIR emissions with photoluminescence quantum yields (PLQY) of 42 (680 nm) and 28%, (709 nm), respectively. Comprehensive time-resolved measurements and dynamics analyses revealed significant differences in the energy transfer pathways, i.e. Förster versus Dexter-type energy transfer between the exciplex host and the fluorescent guest, in which the introduction of bulky tert-butyl groups in the NOz-t-TPA doped film greatly suppressed the Dexter-type energy transfer pathway. Despite the lower PLQY, the analytical simulation predicted NOz-t-TPA to be a better candidate for realizing highly efficient electroluminescence. Confirmation was provided by the performance of the NOz-t-TPA-doped OLED, showing an external quantum efficiency (EQE) of 6.6% with peak wavelength at 710 nm, which is among the best records for the metal-free NIR OLEDs around 710 nm. Insight into energy transfer pathways thus plays a pivotal role in achieving the high-performance OLEDs that incorporate the exciplex host and fluorescent guest.

Graphical abstract: Insights into energy transfer pathways between the exciplex host and fluorescent guest: attaining highly efficient 710 nm electroluminescence

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Supplementary files

Article information


Submitted
26 Feb 2020
Accepted
16 Mar 2020
First published
17 Mar 2020

J. Mater. Chem. C, 2020, Advance Article
Article type
Paper

Insights into energy transfer pathways between the exciplex host and fluorescent guest: attaining highly efficient 710 nm electroluminescence

C. Huang, S. Ho, C. Lai, C. Ko, Y. Wei, J. Lin, D. Chen, T. Ko, K. Wong, Z. Zhang, W. Hung and P. Chou, J. Mater. Chem. C, 2020, Advance Article , DOI: 10.1039/D0TC00986E

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