Transition from Dispersed RTP to Aggregated TADF in Single-Chromophore Polymers

Abstract

Room temperature phosphorescence (RTP) and organic thermally activated delayed fluorescence (TADF) materials have merited enormous application prospects in organic optoelectronics. In spite of this, TADF and RTP dual emissions based on single-chromophore polymers still face a great challenge. In this work, we develop a monomer (CzBT) with twisted electron donating carbazole and electron withdrawing benzothiadiazole (D-A) structure and then copolymerize it with N-isopropylacrylamide (NIPAM) in different ratios to adjust TADF and RTP emission. The polymers exhibit TADF emission from aggregated chromophores, RTP emission with a lifetime of 240 ms from dispersed chromophores, and a high absolute photoluminescence quantum efficiency (20%). Theoretical calculations confirm that the introduction of twisted D-A structure and heteroatoms can not only promote spin orbital coupling to facilitate the accumulation of triplet excitons for RTP emission, but also help RISC to emit TADF in the aggregated state. When applied to solution-processable organic light emitting diodes (OLEDs) devices, excellent current efficiency of 62.7 cd/A and maximum external quantum efficiency of 19.9% were achieved attributing to the dominant TADF emission. This class of polymers paves the way for high-efficiency optoelectronic devices.

Keywords

Thermally activated delayed fluorescence (TADF) / Room temperature phosphorescence (RTP) / Organic light emitting diode (OLED) / Dual emissions

Acknowledgments

We gratefully acknowledge the financial support from the National Natural Science Foundation of China (NNSFC 22175149 and 62375085).

Author Contributions

H.W. executed the experiments and conducted a comprehensive analysis of the data. Y.G. was responsible for the lifetime tests and temperature-variable delayed spectra. Y.W. and F.W. conducted the OLED devices. C.W. helped analyze the experimental data. P.W. conceived and supervised the project, revised and finalized the manuscript. All contributors have given their approval for the submitted version of the manuscript.

Ethics Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

All data generated or analyzed during this study are included in this published article and its supplementary information files.

Funding

This research received no external funding.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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