Delayed fluorescence from inverted singlet and triplet excited states

. Rephrasing this rule for molecular excited states predicts a positive energy gap between spin-singlet and spin-triplet excited states, as has been consistent with numerous experimental observations over almost a century. Here we report a fluorescent molecule that disobeys Hund's rule and has a negative singlet-triplet energy gap of -11 ± 2 meV. The energy inversion of the singlet and triplet excited states results in delayed fluorescence with short time constants of 0.2 μs, which anomalously decrease with decreasing temperature owing to the emissive singlet character of the lowest-energy excited state. Organic light-emitting diodes (OLEDs) using this molecule exhibited a fast transient electroluminescence…

• JS
  Japan Society for the Promotion of Science

  Awards: 24685029, 21H05413, 17H03103, 22H02051, 20H02554, 20K15252
• R
  RIKEN
• PR
  Precursory Research for Embryonic Science and Technology

  Award: JPMJPR17N1