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

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

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

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 (T 1 ) and lowest excited singlet state (S 1 ), so-called ΔE ST , 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 T 1 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 T 1 , probing the suppression of nonradiative decay path of T 1 . 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 T 1 and an increase of spin-orbit coupling together with reducing ΔE ST to achieve a high TADF emission efficiency.

Original languageEnglish
Pages (from-to)62-68
Number of pages7
JournalSynthetic Metals
Volume252
DOIs
Publication statusPublished - Jun 1 2019

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering
  • Metals and Alloys
  • Materials Chemistry

Fingerprint Dive into the research topics of 'TADF activation by solvent freezing: The role of nonradiative triplet decay and spin-orbit coupling in carbazole benzonitrile derivatives'. Together they form a unique fingerprint.

  • Cite this