Hyperfluorescence-Based Emission in Purely Organic Materials: Suppression of Energy-Loss Mechanisms via Alignment of Triplet Excited States,ACS Materials Letters

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Hyperfluorescence-Based Emission in Purely Organic Materials: Suppression of Energy-Loss Mechanisms via Alignment of Triplet Excited States
ACS Materials Letters ( IF 9.6 ) Pub Date : 2020-10-01 , DOI: 10.1021/acsmaterialslett.0c00407
Hadi Abroshan _{1,

2} , Veaceslav Coropceanu _{1,

2} , Jean-Luc Brédas _{1,

2}

Affiliation

Hyperfluorescence has received significant attention as a promising strategy to design organic light-emitting diodes (OLEDs) with high color purity and enhanced stability. In this approach, emitters displaying strong and narrow-band fluorescence are integrated in thin films that contain sensitizers showing efficient thermally activated delayed fluorescence (TADF). To ensure high performance, the energies of the electronic states in the fluorescent emitters must be well-aligned, with respect to those in the TADF molecules, in order to enable a fast rate of Förster singlet-exciton energy transfer from the latter to the former. Here, we performed molecular dynamics simulations and density functional theory calculations to study a series of fluorescent emitters commonly considered in hyperfluorescence OLEDs. For all these emitters, the lowest triplet excited state (T₁^FE) is found to locate substantially below the lowest singlet excited state (S₁^FE). However, the second and/or third triplet excited states (T₂^FE and T₃^FE) appear at an energy close to that of S₁^FE; thus, while energy loss via triplet-exciton Dexter energy transfer from T₁ in TADF molecules to T₁^FE is negligible, it can become significant due to Dexter transfer to T₂^FE and/or T₃^FE. As a result, we propose that fluorescent emitters be designed with a large energy gap between T₂^FE/T₃^FE and S₁^FE, as a promising strategy to suppress any Dexter energy-loss mechanism and develop highly efficient hyperfluorescence-based optoelectronic devices.

中文翻译：

纯有机材料中基于超荧光的发射：通过三重态激发态的对准来抑制能量损失机理。

作为设计具有高色纯度和增强稳定性的有机发光二极管（OLED）的一种有前途的策略，超荧光已受到了广泛的关注。在这种方法中，显示强和窄带荧光的发射器集成在包含敏化剂的薄膜中，该敏化剂显示出有效的热激活延迟荧光（TADF）。为了确保高性能，荧光发射器中电子态的能量必须相对于TADF分子中的电子具有良好的排列，以确保快速将Förster单重态激子能量从后者转移到前者。。在这里，我们进行了分子动力学模拟和密度泛函理论计算，以研究在超荧光OLED中通常考虑的一系列荧光发射器。对于所有这些发射器，发现₁^FE）基本上位于最低单线态激发态（S ₁^FE）之下。然而，第二和/或第三三重态激发态（T ₂^FE和T ₃^FE）以接近于S ₁^FE的能量出现。因此，虽然通过从峰t三重峰-激子德克斯特能量传输的能量损失₁中TADF分子至T ₁^FE是可以忽略不计，它可以成为显著由于德克斯特转移至T ₂^FE和/或T ₃^FE。因此，我们建议设计荧光发射器，使其在T ₂^FE之间具有较大的能隙/ T ₃^FE和S ₁^FE，作为抑制任何Dexter能量损失机制并开发高效的基于超荧光的光电器件的有前途的策略。

更新日期：2020-11-02

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