講演情報
[9a-C214-2]How to make ΔEST of heptazine molecules more negative
〇(P)Liu Guanhao1, Yong-Jin Pu1 (1.RIKEN Center for Emergent Matter Science (CEMS))
キーワード：
Organic electronics、heptazine molecules、photophysical properties
Heptazine derivatives with the energy inversion of the singlet and triplet excited states result in fast delayed fluorescence lifetime (< 1 µs), which hold potential for optoelectronic applications in OLEDs. However, the mechanism of this inversion has not yet been fully elucidated, impeding the molecular design for modulating their photophysical properties.
Here, the relationships between excited states and HOMOs and LUMOs are analyzed, demonstrating that degenerate HOMOs and LUMOs are the key factors in reducing ΔEST due to the stabilization of S1 state. A prescreened heptazine derivative (HzDA3) was estimated to show large negative ΔEST of –244 meV by wavefunction-based quantum chemical calculations (EOM-CCSD). Temperature-dependent TRPL and onset of PL spectra and phosphorescent spectra were measured to experimentally confirm the negative ΔEST (–138 meV), in which HzDA3 showed ultrafast delayed florescence lifetime of 76 ns and fast reverse intersystem crossing rate constant of 107 s-1. To the best of our knowledge, these are the most negative ΔEST and shortest delayed florescence lifetime among the TADF molecules ever reported. This work clarifies the key influence factors in the design of heptazine molecules for inverted singlet-triplet gaps.
Here, the relationships between excited states and HOMOs and LUMOs are analyzed, demonstrating that degenerate HOMOs and LUMOs are the key factors in reducing ΔEST due to the stabilization of S1 state. A prescreened heptazine derivative (HzDA3) was estimated to show large negative ΔEST of –244 meV by wavefunction-based quantum chemical calculations (EOM-CCSD). Temperature-dependent TRPL and onset of PL spectra and phosphorescent spectra were measured to experimentally confirm the negative ΔEST (–138 meV), in which HzDA3 showed ultrafast delayed florescence lifetime of 76 ns and fast reverse intersystem crossing rate constant of 107 s-1. To the best of our knowledge, these are the most negative ΔEST and shortest delayed florescence lifetime among the TADF molecules ever reported. This work clarifies the key influence factors in the design of heptazine molecules for inverted singlet-triplet gaps.