Spontaneous exciton dissociation enables spin state interconversion in delayed fluorescence organic semiconductors - Archive ouverte HAL Access content directly
Journal Articles Nature Communications Year : 2021

Spontaneous exciton dissociation enables spin state interconversion in delayed fluorescence organic semiconductors

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Alexander Gillett
Claire Tonnelé
Giacomo Londi
Gaetano Ricci
  • Function : Author
Darcy Unson
  • Function : Author
David Casanova
Frédéric Castet
Yoann Olivier
  • Function : Author
Weimin Chen
Emrys Evans
Bluebell Drummond
Patrick Conaghan
  • Function : Author
Lin-Song Cui
  • Function : Author
Neil Greenham
Yuttapoom Puttisong
David Beljonne
Richard Friend

Abstract

Engineering a low singlet-triplet energy gap ( ΔE ST ) is necessary for efficient reverse intersystem crossing (rISC) in delayed fluorescence (DF) organic semiconductors but results in a small radiative rate that limits performance in LEDs. Here, we study a model DF material, BF2, that exhibits a strong optical absorption (absorption coefficient = 3.8 × 10 5 cm −1 ) and a relatively large ΔE ST of 0.2 eV. In isolated BF2 molecules, intramolecular rISC is slow (delayed lifetime = 260 μs), but in aggregated films, BF2 generates intermolecular charge transfer (inter-CT) states on picosecond timescales. In contrast to the microsecond intramolecular rISC that is promoted by spin-orbit interactions in most isolated DF molecules, photoluminescence-detected magnetic resonance shows that these inter-CT states undergo rISC mediated by hyperfine interactions on a ~24 ns timescale and have an average electron-hole separation of ≥1.5 nm. Transfer back to the emissive singlet exciton then enables efficient DF and LED operation. Thus, access to these inter-CT states, which is possible even at low BF2 doping concentrations of 4 wt%, resolves the conflicting requirements of fast radiative emission and low ΔE ST in organic DF emitters.

Dates and versions

hal-03436081 , version 1 (19-11-2021)

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Alexander Gillett, Claire Tonnelé, Giacomo Londi, Gaetano Ricci, Manon Catherin, et al.. Spontaneous exciton dissociation enables spin state interconversion in delayed fluorescence organic semiconductors. Nature Communications, 2021, 12, ⟨10.1038/s41467-021-26689-8⟩. ⟨hal-03436081⟩
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