scholarly journals Revisiting the Role of Charge Transfer and Local Excitations in Thermally Activated Delayed Fluorescence

Author(s):  
Leonardo Evaristo de Sousa ◽  
Piotr de Silva

Thermally activated delayed fluorescence (TADF) is a phenomenon that relies on the upconversion of triplet excitons to singlet excitons by means of reverse intersystem crossing (rISC). It has been shown both experimentally and theoretically that the TADF mechanism depends on the interplay between charge transfer and local excitations. However, the difference between the diabatic and adiabatic character of the involved excited states is rarely discussed in the literature. Here, we develop a diabatization procedure to implement a 4-state model Hamiltonian to a set of TADF molecules. We provide physical interpretation for the Hamiltonian elements and show their dependence on the electronic state of the equilibrium geometry. We also demonstrate how vibrations affect TADF efficiency by modifying the diabatic decomposition of the molecule. Finally, we provide a simple model that connects the diabatic Hamiltonian to the electronic properties relevant to TADF and show how such relationship translates into different optimization strategies for rISC, fluorescence and overall TADF performance.

2020 ◽  
Vol 8 (25) ◽  
pp. 8601-8612 ◽  
Author(s):  
Jianzhong Fan ◽  
Yuchen Zhang ◽  
Yuying Ma ◽  
Yuzhi Song ◽  
Lili Lin ◽  
...  

Thermally activated delayed fluorescence (TADF) materials show promising applications in organic light-emitting diodes (OLEDs).


2016 ◽  
Vol 3 (12) ◽  
pp. 1600080 ◽  
Author(s):  
Fernando B. Dias ◽  
Jose Santos ◽  
David R. Graves ◽  
Przemyslaw Data ◽  
Roberto S. Nobuyasu ◽  
...  

2020 ◽  
Author(s):  
Masaki Saigo ◽  
Kiyoshi Miyata ◽  
Hajime Nakanotani ◽  
Chihaya Adachi ◽  
Ken Onda

We have investigated the solvent-dependence of structural changes along with intersystem crossing of a thermally activated delayed fluorescence (TADF) molecule, 3,4,5-tri(9H-carbazole-9-yl)benzonitrile (o-3CzBN), in toluene, tetrahydrofuran, and acetonitrile solutions using time-resolved infrared (TR-IR) spectroscopy and DFT calculations. We found that the geometries of the S1 and T1 states are very similar in all solvents though the photophysical properties mostly depend on the solvent. In addition, the time-dependent DFT calculations based on these geometries suggested that the thermally activated delayed fluorescence process of o-3CzBN is governed more by the higher-lying excited states than by the structural changes in the excited states.<br>


Author(s):  
Yi-Mei Huang ◽  
Tse-Ying Chen ◽  
Deng-Gao Chen ◽  
Hsuan-Chi Liang ◽  
Cheng-Ham Wu ◽  
...  

35Cbz4BzCN, a novel universal host with long triplet lifetime, has been developed. The triplet excitons in 35Cbz4BzCN can be effectively harvested by phosphorescence and thermally activated delayed fluorescence emitters. In...


Molecules ◽  
2021 ◽  
Vol 26 (4) ◽  
pp. 1125
Author(s):  
Teng Teng ◽  
Jinfan Xiong ◽  
Gang Cheng ◽  
Changjiang Zhou ◽  
Xialei Lv ◽  
...  

A new series of tetrahedral heteroleptic copper(I) complexes exhibiting efficient thermally-activated delayed fluorescence (TADF) in green to orange electromagnetic spectral regions has been developed by using D-A type N^N ligand and P^P ligands. Their structures, electrochemical, photophysical, and electroluminescence properties have been characterized. The complexes exhibit high photoluminescence quantum yields (PLQYs) of up to 0.71 at room temperature in doped film and the lifetimes are in a wide range of 4.3–24.1 μs. Density functional theory (DFT) calculations on the complexes reveal the lowest-lying intraligand charge-transfer excited states that are localized on the N^N ligands. Solution-processed organic light emitting diodes (OLEDs) based on one of the new emitters show a maximum external quantum efficiency (EQE) of 7.96%.


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