scholarly journals Thermally Activated Delayed Fluorescence from Locally Excited State: Theoretical Prediction and Experimental Validation

2020 ◽  
Author(s):  
Xiaoxiao Xiao ◽  
Shuai Li ◽  
Hua Geng ◽  
Yuai Duan ◽  
Guo Wang ◽  
...  
Keyword(s):  
Radiative Decay ◽  
Delayed Fluorescence ◽  
Intersystem Crossing ◽  
Decay Rate Constant ◽  
Thermally Activated Delayed Fluorescence ◽  
Locally Excited ◽  
Thermally Activated ◽  
Boron Difluoride ◽  
Novel Design ◽  
Prompt And Delayed Fluorescence

<div>As is well known, the thermally activated delayed fluorescence (TADF) is always generated from charge-transfer (CT) excited states in electron-donor (D) – electron-acceptor (A) systems. Here, a novel design strategy is proposed for realizing TADF from a locally excited (LE) state through controlling the intersystem crossing (ISC) and reverse intersystem crossing (RISC) processes between the LE singlet and higher triplet CT states. Based on the strategy, a boron difluoride derivative is theoretically predicted to emit TADF from the LE state, whose radiative decay rate constant is much larger kr (S<sub>1</sub> →S<sub>0</sub> )=1.12 * 10<sup>8</sup> s <sup>-1</sup> , two orders of magnitude larger than those of common TADF systems. And its lifetimes of the prompt and delayed fluorescence are experimentally validated to be 0.44 ns and 0.7 μs, respectively. This work is a breakthrough in the understanding of TADF and opens a new avenue for extending the TADF materials.</div>

scholarly journals Thermally Activated Delayed Fluorescence from Locally Excited State: Theoretical Prediction and Experimental Validation

2020 ◽  
Author(s):  
Xiaoxiao Xiao ◽  
Shuai Li ◽  
Hua Geng ◽  
Yuai Duan ◽  
Guo Wang ◽  
...  
Keyword(s):  
Radiative Decay ◽  
Delayed Fluorescence ◽  
Intersystem Crossing ◽  
Decay Rate Constant ◽  
Thermally Activated Delayed Fluorescence ◽  
Locally Excited ◽  
Thermally Activated ◽  
Boron Difluoride ◽  
Novel Design ◽  
Prompt And Delayed Fluorescence

<div>As is well known, the thermally activated delayed fluorescence (TADF) is always generated from charge-transfer (CT) excited states in electron-donor (D) – electron-acceptor (A) systems. Here, a novel design strategy is proposed for realizing TADF from a locally excited (LE) state through controlling the intersystem crossing (ISC) and reverse intersystem crossing (RISC) processes between the LE singlet and higher triplet CT states. Based on the strategy, a boron difluoride derivative is theoretically predicted to emit TADF from the LE state, whose radiative decay rate constant is much larger kr (S<sub>1</sub> →S<sub>0</sub> )=1.12 * 10<sup>8</sup> s <sup>-1</sup> , two orders of magnitude larger than those of common TADF systems. And its lifetimes of the prompt and delayed fluorescence are experimentally validated to be 0.44 ns and 0.7 μs, respectively. This work is a breakthrough in the understanding of TADF and opens a new avenue for extending the TADF materials.</div>

All-organic fast intersystem crossing assisted exciplexes exhibiting sub-microsecond thermally activated delayed fluorescence

2021 ◽  
Author(s):  
Kaspars Traskovskis ◽  
Armands Sebris ◽  
Irina Novosjolova ◽  
Maris Turks ◽  
Matas Guzauskas ◽  
...  
Keyword(s):  
Delayed Fluorescence ◽  
Intersystem Crossing ◽  
Thermally Activated Delayed Fluorescence ◽  
Thermally Activated ◽  
Novel Strategy

A novel strategy is presented towards acquisition of exciplex systems exhibiting thermally activated delayed fluorescence (TADF) with high reverse intersystem crossing (RISC) rate (exceeding 107 s-1). This approach involves constructing...

A quantitative description of photoluminescence efficiency of a carbazole-based thermally activated delayed fluorescence emitter

2019 ◽  
Vol 43 (15) ◽  
pp. 6032-6039
Author(s):  
Songyan Feng ◽  
Xugeng Guo ◽  
Jinglai Zhang
Keyword(s):  
Quantitative Description ◽  
Energy Difference ◽  
Delayed Fluorescence ◽  
Intersystem Crossing ◽  
Small Energy ◽  
Thermally Activated Delayed Fluorescence ◽  
Thermally Activated ◽  
Fluorescence Efficiency ◽  
High Fluorescence ◽  
Photoluminescence Efficiency

The present results reveal that the dominant charge transfer characteristics in the S1 and T1 states produce a small energy difference between the two states, and consequently an efficient reverse intersystem crossing process and a high fluorescence efficiency.

Over 20% external quantum efficiency in red thermally activated delayed fluorescence organic light-emitting diodes using a reverse intersystem crossing activating host

2018 ◽  
Vol 6 (20) ◽  
pp. 5363-5368 ◽  
Author(s):  
Ji Han Kim ◽  
Dong Ryun Lee ◽  
Si Hyun Han ◽  
Jun Yeob Lee
Keyword(s):  
Quantum Efficiency ◽  
External Quantum Efficiency ◽  
Light Emitting Diodes ◽  
Delayed Fluorescence ◽  
Organic Light Emitting Diodes ◽  
Intersystem Crossing ◽  
Thermally Activated Delayed Fluorescence ◽  
Light Emitting ◽  
Thermally Activated ◽  
Organic Light

Highly efficient red thermally activated delayed fluorescence organic light-emitting diodes were developed using a reverse intersystem crossing activating host derived from phenylcarbazole and pyridofuropyridine.

scholarly journals A Unified Framework for Photophysical Rate Calculations in TADF Molecules

2021 ◽  
Author(s):  
Leonardo Evaristo de Sousa ◽  
Piotr de Silva
Keyword(s):  
Delayed Fluorescence ◽  
Intersystem Crossing ◽  
Unified Framework ◽  
Thermally Activated Delayed Fluorescence ◽  
Light Emitting ◽  
Thermally Activated ◽  
Theoretical Approaches ◽  
Singlet States ◽  
Photophysical Behavior ◽  
Theoretical Standpoint

One of the challenges in organic light emitting diodes research is finding ways to increase device efficiency by making use of the triplet excitons that are inevitably generated in the process of electroluminescence. One way to do so is by thermally activated delayed fluorescence, a process in which singlet excitons undergo up-conversion to singlet states, allowing them to relax radiatively. The discovery of this phenomenon has ensued a quest for new materials that are able to effectively take advantage of this mechanism. From a theoretical standpoint, this requires the capacity to estimate the rates of the various processes involved in the photophysics of candidate molecules, such as intersystem crossing, reverse intersystem crossing, fluorescence and phosphorescence. Here we present a method that is able to, within a single framework, compute all these rates and predict the photophysics of new molecules. We apply the method to two TADF molecules and show that results compare favorably with other theoretical approaches and experimental results. Finally, we use a kinetic model to show how the calculated rates act in concert to produce different photophysical behavior.

scholarly journals Hot Exciplexes in U-Shaped TADF Molecules with Emission from Locally Excited States

2021 ◽  
Author(s):  
A. Lennart Schleper ◽  
Kenichi Goushi ◽  
Christoph Bannwarth ◽  
Bastian Haehnle ◽  
Philipp Welscher ◽  
...  
Keyword(s):  
Delayed Fluorescence ◽  
Organic Light Emitting Diodes ◽  
Intersystem Crossing ◽  
Thermally Activated Delayed Fluorescence ◽  
New Approach ◽  
Light Emitting ◽  
Thermally Activated ◽  
Donor And Acceptor ◽  
Low Efficiency ◽  
High Color Purity

Rapid reverse intersystem crossing and high color purity are vital characteristics of emitters with thermally activated delayed fluorescence in opto-electronic devices. We present a new approach, called “hot exciplexes” that enables access to both attributes at the same time. Hot exciplexes are produced by coupling facing donor and acceptor moieties to an anthracene bridge, yielding an exciplex with large T1 to T2 spacing. The hot exciplex model is investigated using optical spec-troscopy and quantum chemical simulations. Reverse intersystem crossing is found to occur preferentially from the T3 to the S1 state within only a few nanoseconds. Application and practi-cality of the model are shown by fabrication of organic light-emitting diodes with up to 32 % hot exciplex contribution and low efficiency roll-off.

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