Thermally activated delayed fluorescence as a cycling process between excited singlet and triplet states: Application to the fullerenes

2007 ◽  
Vol 126 (20) ◽  
pp. 204510 ◽  
Author(s):  
Carlos Baleizão ◽  
Mário N. Berberan-Santos
Keyword(s):  
Delayed Fluorescence ◽  
Triplet States ◽  
Excited Singlet ◽  
Thermally Activated Delayed Fluorescence ◽  
Thermally Activated ◽  
Cycling Process ◽  
Singlet And Triplet States

scholarly journals Exploiting trifluoromethyl substituents for tuning orbital character of singlet and triplet states to increase the rate of thermally activated delayed fluorescence

2020 ◽  
Vol 4 (12) ◽  
pp. 3602-3615 ◽  
Author(s):  
Jonathan S. Ward ◽  
Andrew Danos ◽  
Patrycja Stachelek ◽  
Mark A. Fox ◽  
Andrei S. Batsanov ◽  
...  
Keyword(s):  
Excited States ◽  
Organic Molecules ◽  
Delayed Fluorescence ◽  
Triplet States ◽  
Thermally Activated Delayed Fluorescence ◽  
Thermally Activated ◽  
Conjugated Organic Molecules ◽  
Singlet And Triplet States ◽  
Triplet Excited States ◽  
Orbital Character

This work shows that trifluoromethyl (CF3) substituents can be used to increase the rate of thermally activated delayed fluorescence (TADF) in conjugated organic molecules by tuning the excitonic character of the singlet and triplet excited states.

scholarly journals Organic Molecules with Inverted Gaps between First Excited Singlet and Triplet States and Appreciable Fluorescence Rates

2020 ◽  
Author(s):  
Robert Pollice ◽  
Pascal Friederich ◽  
Cyrille Lavigne ◽  
Gabriel dos Passos Gomes ◽  
Alan Aspuru-Guzik
Keyword(s):  
Excited State ◽  
Energy Difference ◽  
Delayed Fluorescence ◽  
Triplet States ◽  
Electron Hole ◽  
Thermally Activated Delayed Fluorescence ◽  
Light Emitting ◽  
Thermally Activated ◽  
Singlet And Triplet States

One of the recent proposals for the design of state-of-the-art emissive materials for organic light emitting diodes (OLEDs) is the principle of thermally activated delayed fluorescence (TADF). The underlying idea is to enable facile thermal upconversion of excited state triplets, which are generated upon electron-hole recombination, to excited state singlets by minimizing the corresponding energy difference resulting in devices with up to 100% internal quantum efficiencies (IQEs). Ideal emissive materials potentially surpassing TADF emitters should have both negative singlet-triplet gaps and appreciable fluorescence rates to maximize reverse intersystem crossing (rISC) rates from excited triplets to singlets while minimizing ISC rates and triplet state occupation leading to long-term operational stability. However, molecules with negative singlet-triplet gaps are extremely rare and, to the best of our knowledge, not emissive. In this work, based on computational studies, we describe the first molecules with negative singlet-triplet gaps and considerable fluorescence rates and show that they are more common than hypothesized previously.

scholarly journals Organic Molecules with Inverted Gaps between First Excited Singlet and Triplet States and Appreciable Fluorescence Rates

2020 ◽  
Author(s):  
Robert Pollice ◽  
Pascal Friederich ◽  
Cyrille Lavigne ◽  
Gabriel dos Passos Gomes ◽  
Alan Aspuru-Guzik
Keyword(s):  
Excited State ◽  
Energy Difference ◽  
Delayed Fluorescence ◽  
Triplet States ◽  
Electron Hole ◽  
Thermally Activated Delayed Fluorescence ◽  
Light Emitting ◽  
Thermally Activated ◽  
Singlet And Triplet States

One of the recent proposals for the design of state-of-the-art emissive materials for organic light emitting diodes (OLEDs) is the principle of thermally activated delayed fluorescence (TADF). The underlying idea is to enable facile thermal upconversion of excited state triplets, which are generated upon electron-hole recombination, to excited state singlets by minimizing the corresponding energy difference resulting in devices with up to 100% internal quantum efficiencies (IQEs). Ideal emissive materials potentially surpassing TADF emitters should have both negative singlet-triplet gaps and appreciable fluorescence rates to maximize reverse intersystem crossing (rISC) rates from excited triplets to singlets while minimizing ISC rates and triplet state occupation leading to long-term operational stability. However, molecules with negative singlet-triplet gaps are extremely rare and, to the best of our knowledge, not emissive. In this work, based on computational studies, we describe the first molecules with negative singlet-triplet gaps and considerable fluorescence rates and show that they are more common than hypothesized previously.

Design of Thermally Activated Delayed Fluorescence Emitters for Organic Solid-State Microlasers

2021 ◽  
Author(s):  
Hongbing Fu ◽  
Shuai Li ◽  
Xue Jin ◽  
Zhenyi Yu ◽  
Xiaoxiao Xiao ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Solid State ◽  
Energy Gap ◽  
Delayed Fluorescence ◽  
Triplet States ◽  
Small Energy ◽  
Thermally Activated Delayed Fluorescence ◽  
Thermally Activated ◽  
Organic Solid ◽  
Singlet And Triplet States

Small energy gap between charge transfer (CT) singlet and triplet states enables thermally activated delayed fluorescence (TADF). Nevertheless, the small oscillator strength associated with CT states and their long exciton...

Study of an Oxadiazole Derivative for a Blue Thermally Activated Delayed Fluorescence Emitter

2015 ◽  
Vol 15 (10) ◽  
pp. 7828-7831 ◽  
Author(s):  
Dong Yuel Kwon ◽  
Geon Hyeong Lee ◽  
Young Sik Kim
Keyword(s):  
Excited States ◽  
Energy Gap ◽  
Delayed Fluorescence ◽  
Excited Singlet ◽  
Thermally Activated Delayed Fluorescence ◽  
Excited Triplet ◽  
Thermally Activated ◽  
Donor And Acceptor ◽  
Homo And Lumo ◽  
Dft And Tddft Calculations

Novel thermally activated delayed fluorescence (TADF) materials (ACR-OXD, 2ACR-OXD) with 9,10- dihydro-9,9-dimethylacridine (ACR) as an electron donor and oxadiazole derivative (OXD) as an electron acceptor were designed and theoretically investigated for blue OLED emitter. Using DFT and TDDFT calculations, we gained the electron distribution of HOMO and LUMO and the energy of the lowest singlet (S1) and the lowest triplet (T1) excited states. In comparison with the previously reported a xanthen derivative (ACR-XTN), ACR-OXD exhibits a promising blue TADF emitter because of destabilizing the LUMO of ACR-OXD by the change of the electron accepting group and maintaining the steric hindrance between donor and acceptor moieties which lead to efficient TADF due to the small energy gap between the lowest excited singlet (S1) state and the lowest excited triplet (T1) state.

scholarly journals Using the Mechanical Bond to Tune the Performance of a Thermally Activated Delayed Fluorescence Emitter

2021 ◽  
Author(s):  
P Rajamalli ◽  
Federica Rizzi ◽  
Wenbo Li ◽  
Michael Jinks ◽  
Abhishek Gupta ◽  
...  
Keyword(s):  
Weak Interactions ◽  
Photophysical Properties ◽  
Energy Difference ◽  
Delayed Fluorescence ◽  
Fine Tuning ◽  
Triplet States ◽  
Thermally Activated Delayed Fluorescence ◽  
X Ray Crystallography ◽  
Thermally Activated ◽  
Mechanical Bond

We report the characterization of rotaxanes based on a carbazole–benzophenone thermally activated delayed fluorescence luminophore. We find that the mechanical bond leads to an improvement in key photophysical properties of the emitter, notably an increase in photoluminescence quantum yield and a decrease in the energy difference between singlet and triplet states, as well as fine tuning of the emission wavelength, a feat that is difficult to achieve when using covalently bound substituents. Computational simulations, supported by X-ray crystallography, suggest that this tuning of properties occurs due to weak interactions between the axle and the macrocycle that are enforced by the mechanical bond. This work highlights the benefits of using the mechanical bond to refine existing luminophores, providing a new avenue for emitter optimization that can ultimately increase the performance of these molecules.

scholarly journals Extremely condensing triplet states of DPEPO-type hosts through constitutional isomerization for high-efficiency deep-blue thermally activated delayed fluorescence diodes

2016 ◽  
Vol 7 (4) ◽  
pp. 2870-2882 ◽  
Author(s):  
Jing Zhang ◽  
Dongxue Ding ◽  
Ying Wei ◽  
Hui Xu
Keyword(s):  
Quantum Efficiency ◽  
External Quantum Efficiency ◽  
High Efficiency ◽  
State Of The Art ◽  
Delayed Fluorescence ◽  
Triplet States ◽  
Thermally Activated Delayed Fluorescence ◽  
Thermally Activated ◽  
Deep Blue ◽  
Art Performance

An asymmetric constitutional isomer of the thermally activated delayed fluorescence (TADF) host DPEPO, named 24′DPEPO, endowed deep-blue TADF diodes with state-of-the-art performance, including external quantum efficiency beyond 20%.

scholarly journals TRANSPORT PROPERTIES OF PENTACENE, HEXACENE AND THEIR BN ANALOGUES

2016 ◽  
Vol 7 (1) ◽  
Author(s):  
Stevan Armaković ◽  
Sanja J. Armaković ◽  
Svetlana S. Pelemiš ◽  
Blanka Škipina ◽  
Igor Hut
Keyword(s):  
Dft Calculations ◽  
Transport Properties ◽  
Delayed Fluorescence ◽  
Energy Separation ◽  
Excited Singlet ◽  
Thermally Activated Delayed Fluorescence ◽  
Thermally Activated ◽  
Charge Hopping ◽  
Reorganization Energies ◽  
Non Equilibrium Green’S Function

We have investigated transport properties of higher acenes pentacene and hexacene and compared it with the transport properties of their BN analogues. Charge hopping from one structure to another was investigated through calculations of reorganization energies based on DFT and Marcus semiempiric approach, while the investigation of charge transport along the investigated structures was based on DFT calculations and non-equilibrium Green's function (NEGF) method. Attention was also paid to the energy separation between the lowest excited singlet (S1) and triplet (T1) state, which is quantity that is important for the field of thermally activated delayed fluorescence (TADF). The obtained results indicate that both groups of investigated structures have certain advantages and drawbacks. According to the reorganization energies and I-V characteristics, pentacene and hexacene have better properties, while from the aspect of TADF, BN analogues of pentacene and hexacene have better properties.

scholarly journals Molecular Design Realizing Very Fast Reverse Intersystem Crossing in Purely Organic Emitter

2019 ◽  
Author(s):  
yoshimasa wada ◽  
Hiromichi Nakagawa ◽  
Soma Matsumoto ◽  
Yasuaki Wakisaka ◽  
Hironori Kaji
Keyword(s):  
Energy Gap ◽  
Molecular Design ◽  
Delayed Fluorescence ◽  
Intersystem Crossing ◽  
Triplet States ◽  
Thermally Activated Delayed Fluorescence ◽  
Light Emitting ◽  
Thermally Activated ◽  
Donor And Acceptor ◽  
Spin Inversion

Reverse intersystem crossing (RISC), originally considered forbidden in purely organic materials, has been recently enabled by minimizing the energy gap between the lowest singlet excited state (S<sub>1</sub>) and lowest triplet state (T<sub>1</sub>) in thermally activated delayed fluorescence (TADF) systems. However, direct spin-inversion between S<sub>1</sub> and T<sub>1</sub> is still inefficient when both states are of the same charge transfer (CT) nature (i.e. <sup>1</sup>CT and <sup>3</sup>CT, respectively). Intervention of locally excited triplet states (<sup>3</sup>LE) between <sup>1</sup>CT and <sup>3</sup>CT is expected to trigger fast spin-flip. Here, we report on the systematic-design of the ideal TADF molecules with near-degenerate <sup>1</sup>CT, <sup>3</sup>CT and <sup>3</sup>LE states by controlling the through-space distance between the donor and acceptor segments in a molecule with tilted intersegment angles. The new system realizes very fast RISC with a rate constant (<i>k</i><sub>RISC</sub>) of 1.2×10<sup>7</sup> s<sup>−1</sup>. The large <i>k</i><sub>RISC</sub> of the emitter resulted in great device performance in the applications to blue TADF assisted fluorescence organic light-emitting diodes (OLEDs) as well as TADF-emitter OLEDs.<br>

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