Suppression of Structural Change upon S 1 -T 1 Conversion Assists the Thermally Activated Delayed Fluorescence Process in Carbazole-Benzonitrile Derivatives

Masaki Saigo, Kiyoshi Miyata, Sei'Ichi Tanaka, Hajime Nakanotani, Chihaya Adachi, Ken Onda

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)

Abstract

Thermally activated delayed fluorescence (TADF) molecules are gathering attention for their potential to boost the efficiency of organic light-emitting diodes without precious metals. Minimizing the energy difference between the S 1 and T 1 states (ΔE ST ) is a fundamental strategy to accelerate reverse intersystem crossing (RISC). However, the lack of microscopic understanding of the process prevents adequate design strategies for efficient TADF materials. Here, we focused on four carbazole-benzonitrile (Cz-BN) derivatives that possess identical ΔE ST but distinct TADF activities. We systematically compared their geometrical dynamics upon photoexcitation using time-resolved infrared (TR-IR) vibrational spectroscopy in conjunction with quantum chemical calculations. We found that the most TADF-active molecule, 4CzBN, shows little structural change after photoexcitation, while the TADF-inactive molecules show relatively large deformation upon S 1 -T 1 conversion. This implies that the suppression of structural deformation is critical for minimizing the activation energy barrier for RISC in cases of the Cz-BN derivatives.

Original languageEnglish
Pages (from-to)2475-2480
Number of pages6
JournalJournal of Physical Chemistry Letters
Volume10
Issue number10
DOIs
Publication statusPublished - May 16 2019

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Physical and Theoretical Chemistry

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