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...

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.

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>

scholarly journals N-Rich Electron Acceptor: Triplet Harvesting in Multichromophoric Pyridoquinoxaline and Pyridopyrazine-Based Organic Emitters

2020 ◽  
Author(s):  
BAHADUR SK ◽  
Samarth Sharma ◽  
Anto James ◽  
Subhankar Kundu ◽  
Abhijit Patra
Keyword(s):  
Energy Gap ◽  
Delayed Fluorescence ◽  
Triplet States ◽  
Triplet Energy ◽  
Thermally Activated Delayed Fluorescence ◽  
Thermally Activated ◽  
New Class ◽  
State Security ◽  
Linkage Position ◽  
Triplet Harvesting

<p></p><p>Control of nonradiative deactivation of triplet states and tuning the singlet-triplet energy gap (ΔE<sub>ST</sub>) are the major challenges to develop materials exhibiting thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP). Herein, we propose a new class of multichromophoric tridonor-acceptor (D<sub>3</sub>-A) compounds with rigid and flexible π-spacer having N-rich pyridoquinoxaline (PQ) and pyridopyrazine (PZ) acceptor core, respectively. The molecule with carbazole (Cz) donors at <i>meta</i> to quinoxaline (QX) nitrogen of rigid PQ core exhibits TADF. Whereas, the variation of the linkage position of Cz to PQ as well as twisted and flexible PZ core show predominantly RTP due to relatively higher singlet-triplet energy gap (ΔE<sub>ST</sub>). Increasing the donor strength with phenoxazine (PO) in PZ system leads to simultaneous TADF and RTP. Further, we demonstrate the promising scope of all-organic triplet harvesting materials in solid-state security encryption.</p><br><p></p>

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>

scholarly journals N-Rich Electron Acceptor: Triplet Harvesting in Multichromophoric Pyridoquinoxaline and Pyridopyrazine-Based Organic Emitters

2020 ◽  
Author(s):  
BAHADUR SK ◽  
Samarth Sharma ◽  
Anto James ◽  
Subhankar Kundu ◽  
Abhijit Patra
Keyword(s):  
Energy Gap ◽  
Delayed Fluorescence ◽  
Triplet States ◽  
Triplet Energy ◽  
Thermally Activated Delayed Fluorescence ◽  
Thermally Activated ◽  
New Class ◽  
State Security ◽  
Linkage Position ◽  
Triplet Harvesting

<p></p><p>Control of nonradiative deactivation of triplet states and tuning the singlet-triplet energy gap (ΔE<sub>ST</sub>) are the major challenges to develop materials exhibiting thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP). Herein, we propose a new class of multichromophoric tridonor-acceptor (D<sub>3</sub>-A) compounds with rigid and flexible π-spacer having N-rich pyridoquinoxaline (PQ) and pyridopyrazine (PZ) acceptor core, respectively. The molecule with carbazole (Cz) donors at <i>meta</i> to quinoxaline (QX) nitrogen of rigid PQ core exhibits TADF. Whereas, the variation of the linkage position of Cz to PQ as well as twisted and flexible PZ core show predominantly RTP due to relatively higher singlet-triplet energy gap (ΔE<sub>ST</sub>). Increasing the donor strength with phenoxazine (PO) in PZ system leads to simultaneous TADF and RTP. Further, we demonstrate the promising scope of all-organic triplet harvesting materials in solid-state security encryption.</p><br><p></p>

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