TADF activation by solvent freezing: The role of nonradiative triplet decay and spin-orbit coupling in carbazole benzonitrile derivatives

T. Hosokai, H. Nakanotani, S. Santou, H. Noda, Y. Nakayama, C. Adachi

研究成果: ジャーナルへの寄稿学術誌査読

12 被引用数 (Scopus)

抄録

Thermally activated delayed fluorescence (TADF) materials have attracted considerable attentions as a new kind of emitters in organic light-emitting diodes. While it is requisite to minimize an energy difference between the lowest excited triplet state (T1) and lowest excited singlet state (S1), so-called ΔEST, a deeper understanding of the emission mechanism is desirable to clarify the comprehensive molecular design. In this paper, we present that the TADF ability and efficiency of (rare-)metal free organic molecules are surely influenced by both the nonradiative decay of T1 and spin-orbit coupling. By investigating a temperature dependent photoluminescence of carbazole benzonitrile derivatives in toluene solutions using a newly developed liquid nitrogen cryostat, we demonstrate the activation of TADF by solvent freezing for room temperature-TADF inactive molecules. Transient photoluminescence measurements of the frozen samples show a significant increase of a lifetime of T1, probing the suppression of nonradiative decay path of T1. A magnitude of the TADF activation by the solvent freezing is closely related to the degree of spin-orbit coupling of the molecules. The present results emphasize the importance of suppression of nonradiative decay of T1 and an increase of spin-orbit coupling together with reducing ΔEST to achieve a high TADF emission efficiency.

本文言語英語
ページ(範囲)62-68
ページ数7
ジャーナルSynthetic Metals
252
DOI
出版ステータス出版済み - 6月 2019

!!!All Science Journal Classification (ASJC) codes

  • 電子材料、光学材料、および磁性材料
  • 凝縮系物理学
  • 材料力学
  • 機械工学
  • 金属および合金
  • 材料化学

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