Dual intramolecular charge-transfer fluorescence derived from a phenothiazine-triphenyltriazine derivative

Hiroyuki Tanaka, Katsuyuki Shizu, Hajime Nakanotani, Chihaya Adachi

Research output: Contribution to journalArticle

141 Citations (Scopus)

Abstract

A material containing a phenothiazine (PTZ) electron donor unit and 2,4,6-triphenyl-1,3,5-triazine (TRZ) electron acceptor unit, PTZ-TRZ, which exhibits thermally activated delayed fluorescence (TADF) was developed. Density functional theory calculations revealed the existence of two ground-state conformers with different energy gaps between the lowest singlet excited state and lowest triplet excited state (1.14 and 0.18 eV), which resulted from the distortion of PTZ, as confirmed by X-ray structure analysis. PTZ-TRZ in toluene solution showed two broad, structureless emissions, confirming the existence of two different excited states. From detailed analyses of the absorption and photoluminescence spectra, we determined that both emissions were intramolecular charge-transfer (ICT) fluorescence. Therefore, the excited-state conformers of PTZ-TRZ resulted in dual ICT fluorescence. Because previously reported dual fluorescence from single molecules involves locally excited and ICT fluorescence, the dual ICT fluorescence from PTZ-TRZ is novel. Temperature-dependence of transient PL spectra of a 2 wt % PTZ-TRZ-doped film in 3,3′-bis(N-carbazolyl)-1, 1′-biphenyl measured by a streak camera revealed that the former and latter emissions were independent of and dependent on the film temperature, respectively. This confirms that the dual fluorescence involves TADF characteristics. An organic light-emitting diode containing PTZ-TRZ exhibited a maximum external quantum efficiency of 10.8 ± 0.5% with dual ICT fluorescence.

Original languageEnglish
Pages (from-to)15985-15994
Number of pages10
JournalJournal of Physical Chemistry C
Volume118
Issue number29
DOIs
Publication statusPublished - Jul 24 2014

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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