Thermal equilibration between singlet and triplet excited states in organic fluorophore for submicrosecond delayed fluorescence

Naoya Aizawa, Akinobu Matsumoto, Takuma Yasuda

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)

Abstract

In any complex molecular system, electronic excited states with different spin multiplicities can be described via a simple statistical thermodynamic formalism if the states are in thermal equilibrium. However, this ideal situation has hitherto been infeasible for efficient fluorescent organic molecules. Here, we report a highly emissive metal-free purely organic fluorophore that enables thermal equilibration between singlet and triplet excited states. The key to this unconventional excitonic behavior is the exceptionally fast spin-flipping reverse intersystem crossing from the triplet to singlet excited states with a rate constant exceeding 108 per second, which is considerably higher than that of radiative decay (fluorescence) from the singlet excited state. The present fluorophoric system exhibits an emission lifetime as short as 750 nanoseconds and, therefore, allows organic light-emitting diodes to demonstrate external electroluminescence quantum efficiency exceeding 20% even at a practical high luminance of more than 10,000 candelas per square meter.

Original languageEnglish
Article numbereabe5769
JournalScience Advances
Volume7
Issue number7
DOIs
Publication statusPublished - Feb 12 2021

All Science Journal Classification (ASJC) codes

  • General

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