Effect of atom substitution in chalcogenodiazole-containing thermally activated delayed fluorescence emitters on radiationless transition

Hiroyuki Tanaka, Katsuyuki Shizu, Jiyoung Lee, Chihaya Adachi

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40 Citations (Scopus)

Abstract

Radiationless transition between the lowest singlet (S1) and triplet (T1) excited states in the thermally activated delayed fluorescence (TADF) were investigated with respect to molecular design. The photophysical, transient photoluminescence and electroluminescence (EL) characteristics of two chalcogenodiazole-containing TADF emitters were compared. These contained 1,3,4-oxadiazole or 1,3,4-thiadiazole. The effect of substituting oxygen with sulfur on TADF was caused by an electron-pair-accepting conjugative effect. This effect resulted from the vacant 3d-orbitals of divalent sulfur in the thiadiazole heteroring. Atom substitution narrowed the gap between the highest occupied and lowest unoccupied molecular orbital energy levels, and enhanced S1 → T1 intersystem crossing. These effects resulted from the enhanced acceptor strength and orbital angular momentum by the vacant 3d-orbitals of sulfur. Atom substitution increased the contribution of the delayed fluorescence component to the total EL efficiency (65.1% → 78.0%). This resulted from enhanced reverse intersystem crossing, because of the reduced energy gap between S1 and T1.

Original languageEnglish
Pages (from-to)2948-2955
Number of pages8
JournalJournal of Physical Chemistry C
Volume119
Issue number6
DOIs
Publication statusPublished - Feb 12 2015

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

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