peri-Acenoacene Molecules: Tuning of the Singlet and Triplet Excitation Energies by Modifying their Radical Character

2021 ◽  
Author(s):  
Alicia Omist ◽  
Gaetano Ricci ◽  
Amel Derradji ◽  
Ángel J. José Pérez-Jiménez ◽  
Emilio San Fabián ◽  
...  
Keyword(s):  
Light Emission ◽  
Energy Difference ◽  
Delayed Fluorescence ◽  
Excitation Energies ◽  
Thermally Activated Delayed Fluorescence ◽  
Triplet Excitation ◽  
Thermally Activated ◽  
Radical Character ◽  
Triplet Excitons

The energy difference between singlet and triplet excitons, or ΔEST, is a key magnitude for novel light-emission mechanisms (i.e., TADF or Thermally Activated Delayed Fluorescence) or other photoactivated processes. We...

scholarly journals Computational Studies of Molecular Materials for Unconventional Energy Conversion: The Challenge of Light Emission by Thermally Activated Delayed Fluorescence

Molecules ◽  
2020 ◽  
Vol 25 (4) ◽  
pp. 1006 ◽  
Author(s):  
Javier Sanz-Rodrigo ◽  
Yoann Olivier ◽  
Juan-Carlos Sancho-García
Keyword(s):  
Energy Savings ◽  
Light Emission ◽  
Computational Modelling ◽  
Energy Difference ◽  
Delayed Fluorescence ◽  
Structure Property ◽  
Triplet Energy ◽  
Thermally Activated Delayed Fluorescence ◽  
Thermally Activated ◽  
Structure Property Relationships

In this paper we describe the mechanism of light emission through thermally activated delayed fluorescence (TADF)—a process able to ideally achieve 100% quantum efficiencies upon fully harvesting the energy of triplet excitons, and thus minimizing the energy loss of common (i.e., fluorescence and phosphorescence) luminescence processes. If successful, this technology could be exploited for the manufacture of more efficient organic light-emitting diodes (OLEDs) made of only light elements for multiple daily applications, thus contributing to the rise of a sustainable electronic industry and energy savings worldwide. Computational and theoretical studies have fostered the design of these all-organic molecular emitters by disclosing helpful structure–property relationships and/or analyzing the physical origin of this mechanism. However, as the field advances further, some limitations have also appeared, particularly affecting TD-DFT calculations, which have prompted the use of a variety of methods at the molecular scale in recent years. Herein we try to provide a guide for beginners, after summarizing the current state-of-the-art of the most employed theoretical methods focusing on the singlet–triplet energy difference, with the additional aim of motivating complementary studies revealing the stronger and weaker aspects of computational modelling for this cutting-edge technology.

Why Triage the Materials with Low Luminescence Quantum Efficiency: The Use of 35Cbz4BzCN as a Universal Host for Organic Light Emitting Diode through Effective Triplet Energy Transfer

2021 ◽  
Author(s):  
Yi-Mei Huang ◽  
Tse-Ying Chen ◽  
Deng-Gao Chen ◽  
Hsuan-Chi Liang ◽  
Cheng-Ham Wu ◽  
...  
Keyword(s):  
Light Emitting Diode ◽  
Delayed Fluorescence ◽  
Triplet Energy ◽  
Thermally Activated Delayed Fluorescence ◽  
Light Emitting ◽  
Organic Light Emitting Diode ◽  
Thermally Activated ◽  
Triplet Energy Transfer ◽  
Triplet Lifetime ◽  
Triplet Excitons

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...

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.

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 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.

Recent advances in organic thermally activated delayed fluorescence materials

2017 ◽  
Vol 46 (3) ◽  
pp. 915-1016 ◽  
Author(s):  
Zhiyong Yang ◽  
Zhu Mao ◽  
Zongliang Xie ◽  
Yi Zhang ◽  
Siwei Liu ◽  
...  
Keyword(s):  
Delayed Fluorescence ◽  
Thermally Activated Delayed Fluorescence ◽  
Thermally Activated ◽  
Recent Advances ◽  
Triplet Excitons

Thermally activated delayed fluorescence: harvesting dark triplet excitons to generate bright emissive singlet excitons.

Polarity-dependent solvatochromic properties of thermally activated delayed fluorescence with donor–acceptor constituents under different excitation energies

2021 ◽  
Vol 9 (39) ◽  
pp. 13935-13941
Author(s):  
Haiyang Xu ◽  
Shuzhe Li ◽  
Minyu Chen ◽  
Yachen Xu ◽  
Pengchao Zhou ◽  
...  
Keyword(s):  
Delayed Fluorescence ◽  
Excitation Energies ◽  
Thermally Activated Delayed Fluorescence ◽  
Thermally Activated ◽  
Donor Acceptor

The polarity-dependent solvatochromic properties of a D–A structure molecule under different excitation energies are reported.

Theoretical Study on Benzazole Derivatives for Use in Blue Thermally Activated Delayed Fluorescence Emitters

2015 ◽  
Vol 15 (10) ◽  
pp. 7819-7822 ◽  
Author(s):  
Dong Yuel Kwon ◽  
Geon Hyeong Lee ◽  
Young Sik Kim
Keyword(s):  
Density Functional Theory ◽  
Molecular Orbital ◽  
Density Functional ◽  
Light Emitting Diode ◽  
Energy Difference ◽  
Delayed Fluorescence ◽  
Functional Theory ◽  
Thermally Activated Delayed Fluorescence ◽  
Organic Light Emitting Diode ◽  
Thermally Activated

Four novel thermally activated delayed fluorescence (TADF) materials with 9,10-dihydro-9,9- dimethylacridine (DMAC) and phenylindolo(2,3-a)carbazole (PIC) as electron donors and benzazole derivatives (BO, and BT) as electron acceptors (DMAC-BO, DMAC-BT, PIC-BO, and PIC-BT) were designed and theoretically investigated for use as a blue organic light emitting diode (OLED) emitter. Using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations, we calculated the electron distribution of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), and the energy of the lowest singlet (S1) and the lowest triplet (T1) excited states. All the dyes had a small spatial overlap between the HOMO and LUMO because of the relatively large dihedral angle between the phenyl ring and the acceptor moiety. In terms of the energy difference (ΔEST) between the S1 state and the T1 state, DMAC-BO and DMAC-BT showed the small ΔEST (0.18 eV and 0.21 eV, respectively). However, PIC-BO and PIC-BT showed the large ΔEST (0.62 eV and 0.61 eV, respectively). Among the TADF materials, we showed that DMAC-BO would have the best TADF properties in terms of small ΔEST and blue OLED emitters

Thermally activated delayed fluorescence material with aggregation-induced emission properties for highly efficient organic light-emitting diodes

2018 ◽  
Vol 6 (11) ◽  
pp. 2873-2881 ◽  
Author(s):  
Yaodong Zhao ◽  
Weigao Wang ◽  
Chen Gui ◽  
Li Fang ◽  
Xinlei Zhang ◽  
...  
Keyword(s):  
Delayed Fluorescence ◽  
Organic Light Emitting Diodes ◽  
Luminescent Materials ◽  
Thermally Activated Delayed Fluorescence ◽  
Light Emitting ◽  
Aggregation Induced Emission ◽  
Thermally Activated ◽  
Organic Light ◽  
Fluorescence Material ◽  
Triplet Excitons

Luminescent materials with aggregation-induced emission (AIE) properties exhibit high solid state emission, while thermally activated delayed fluorescence (TADF) materials can fully harvest singlet and triplet excitons to achieve efficient electroluminescence (EL).

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