Real-time Observation of Electron-Phonon Dynamics in Organic Materials for Optoelectronics Using Ulfrafast Spectroscopy

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• Professor Kiyoshi Miyata, Department of Chemistry, Kyushu University, Japan
• Friday 06 March 2020, 14:00-15:00
• Electrical Engineering, Department of Engineering - EED Seminar Room - 9 JJ Thomson Avenue, Cambridge, CB3 0FA.

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Microscopic understanding of exciton and carrier physics in functional molecules represents a great challenge, because of their complexity resulting from the strong electron-phonon coupling. It is of great importance to probe not only electron dynamics but also structural dynamics for gaining mechanistic details of their functions [1-5]. Here I show a couple of successful applications of ultrafast spectroscopy to probe the structural/geometrical dynamics of functional materials associated with photo-induced electron dynamics.

I will mainly talk about systematic studies on thermally activated delayed fluorescence (TADF) molecules using time-resolved infrared spectroscopy (TR-IR). TADF is gathering attention for its potential to boost the efficiency of organic light-emitting diodes without using precious metals, but the mechanistic details along intersystem crossing remain elusive. By probing the structural dynamics of the TADF materials using TR-IR, we discuss molecular-level understandings of TADF dynamics from the viewpoint of molecular geometry in the excited states. Our findings clearly show that controlling geometrical configuration in excited states is key to the efficiency of TADF [1].

• This work was supported by the JSPS Core-to-Core Program

References:

[1] Masaki Saigo, Kiyoshi Miyata, Sei’ichi Tanaka, Hajime Nakanotani, Chihaya Adachi, Ken Onda, “Suppression of Structural Change upon S1–T1 Conversion Assists the Thermally Activated Delayed Fluorescence Process in Carbazole-Benzonitrile Derivatives”, J. Phys. Chem. Lett. 10, 2475 (2019).

[2] Kiyoshi Miyata, X.-Y. Zhu, “Ferroelectric large polarons”, Nature Mater. 17, 379 (2018).

[3] Haiming Zhu†, Kiyoshi Miyata†, Yongping Fu, Jue Wang, Prakriti P Joshi, Daniel Niesner, Kristopher W Williams, Song Jin, X-Y Zhu, “Screening in crystalline liquids protects energetic carriers in hybrid perovskites”, Science 353, 1409-1413 (2017).

[4] Kiyoshi Miyata, Daniele Meggiolaro, M Tuan Trinh, Prakriti P Joshi, Edoardo Mosconi, Skyler C Jones, Filippo De Angelis, X-Y Zhu, “Large polarons in lead halide perovskites” Science Adv. 3, e1701217 (2017).

[5] Kiyoshi Miyata, Yuki Kurashige, Kazuya Watanabe, Toshiki Sugimoto, Shota Takahashi, Shunsuke Tanaka, Jun Takeya, Takeshi Yanai, Yoshiyasu Matsumoto, “Coherent singlet fission activated by symmetry breaking” Nature Chem. 9, 983–989 (2017).

This talk is part of the Electrical Engineering series.

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