A light-emitting mechanism for organic light-emitting diodes: Molecular design for inverted singlet-triplet structure and symmetry-controlled thermally activated delayed fluorescence

Tohru Sato, Motoyuki Uejima, Kazuyoshi Tanaka, Hironori Kaji, Chihaya Adachi

Research output: Contribution to journalArticle

33 Citations (Scopus)

Abstract

The concepts of symmetry-controlled thermally activated delayed fluorescence (SC-TADF) and inverted singlet-triplet (iST) structure are proposed. Molecules that can exhibit SC-TADF or have an iST structure can be employed as light-emitting molecules in organic light-emitting diodes. The molecular symmetry plays crucial roles in these concepts since they are based on the selection rules for the electric dipole transition, intersystem crossing, and nonradiative vibronic (electron-vibration) transitions. In addition to the symmetry conditions for the SC-TADF and iST molecules, the molecules should have small diagonal and off-diagonal vibronic coupling constants for suppressing vibrational relaxations and nonradiative vibronic transitions, respectively, and a large transition dipole moment for the fluorescence process. Analyses using the vibronic coupling and transition dipole moment densities are employed to reduce the vibronic coupling constants and to increase the transition dipole moment. The preferable point groups in the development of SC-TADF and iST molecules are discussed on the basis of the ratios of forbidden pairs of irreducible representations. It is found that the existence of the inversion symmetry is preferable for designing SC-TADF and iST molecules. On the basis of these guiding principles, we designed some anthracene and pyrene derivatives as candidate iST molecules. Their electronic structures, spin-orbit couplings, transition dipole moments, and vibronic couplings are discussed.

Original languageEnglish
Pages (from-to)870-878
Number of pages9
JournalJournal of Materials Chemistry C
Volume3
Issue number4
DOIs
Publication statusPublished - Jan 28 2015

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Organic light emitting diodes (OLED)
Fluorescence
Dipole moment
Molecules
Electron transitions
Point groups
Anthracene
Pyrene
Electronic structure
Orbits
Derivatives
Electrons

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Materials Chemistry

Cite this

A light-emitting mechanism for organic light-emitting diodes : Molecular design for inverted singlet-triplet structure and symmetry-controlled thermally activated delayed fluorescence. / Sato, Tohru; Uejima, Motoyuki; Tanaka, Kazuyoshi; Kaji, Hironori; Adachi, Chihaya.

In: Journal of Materials Chemistry C, Vol. 3, No. 4, 28.01.2015, p. 870-878.

Research output: Contribution to journalArticle

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