Red Light-Emitting Thermally-Activated Delayed Fluorescence of Naphthalimide-Phenoxazine Electron Donor-Acceptor Dyad: Time-Resolved Optical and Magnetic Spectroscopic Studies

Xue Zhang, Xiao Liu, Maria Taddei, Laura Bussotti, Ivan Kurganskii, Minjie Li, Xiao Jiang, Longjiang Xing, Shaomin Ji, Yanping Huo, Jianzhang Zhao, Mariangela Di Donato, Yan Wan, Zujin Zhao, Matvey V. Fedin

Результат исследования: Научные публикации в периодических изданияхстатьярецензирование

Аннотация

We prepared an orthogonal compact electron-donor (phenoxazine, PXZ)-acceptor (naphthalimide, NI) dyad (NI-PXZ), to study the photophysics of the thermally-activated delayed fluorescence (TADF), which has a luminescence lifetime of 16.4 ns (99.2 %)/17.0 μs (0.80 %). A weak charge transfer (CT) absorption band was observed for the dyad, indicating non-negligible electronic coupling between the donor and acceptor at the ground state. Femtosecond transient absorption spectroscopy shows a fast charge separation (CS) (ca. 2.02∼2.72 ps), the majority of the singlet CS state is short-lived, especially in polar solvents (τCR = 10.3 ps in acetonitrile, vs. 1.83 ns in toluene, 7.81 ns in n-hexane). Nanosecond transient absorption spectroscopy detects a long-lived transient species in n-hexane, which is with a mixed triplet local excited state (3LE) and charge separated state (3CS), the lifetime is 15.4 μs. In polar solvents, such as tetrahydrofuran and acetonitrile, a neat 3CS state was observed, whose lifetimes are 226 ns and 142 ns, respectively. Time-resolved electron paramagnetic resonance (TREPR) spectra indicate the existence of strongly spin exchanged 3LE/3CT states, with the effective zero field splitting (ZFS) |D| and |E| parameters of 1484 MHz and 109 MHz, respectively, much smaller than that of the native 3NI state (2475 and 135 MHz). It is rare but solid experimental evidence that a closely-lying 3LE state is crucial for occurrence of TADF and this 3LE state is an essential intermediate state to facilitate reverse intersystem crossing in TADF systems.

Язык оригиналаанглийский
Число страниц16
ЖурналChemistry - A European Journal
Том28
Номер выпуска37
Ранняя дата в режиме онлайн19 апр 2022
DOI
СостояниеЭлектронная публикация перед печатью - 19 апр 2022

Предметные области OECD FOS+WOS

  • 2.04 ХИМИЧЕСКИЕ ТЕХНОЛОГИИ
  • 1.04 ХИМИЧЕСКИЕ НАУКИ

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