Dynamic nature of excited states of donor–acceptor TADF materials for OLEDs: how theory can reveal structure–property relationships

Olivier, Yoann; Moral, Mónica; Muccioli, Luca; Sancho-García, Juan-Carlos

doi:10.1039/c6tc05075a

Cited by 121 publications

(112 citation statements)

References 65 publications

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“…We remind that some of us and others have found before a direct correlation between low

Δ E^{ST}

values and high (low) values of

Δ r

(

ϕ_{S}

), an issue that we would like to further corroborate here. Actually, Figure displays the existing interplay (or correlation) between some of the variables monitored (

Δ E_{v}^{S T}, ϕ_{S} (S_{1})

, and

Δ r (S_{1})

) and indicates how this is indeed the case.…”

Section: Resultssupporting

confidence: 80%

“…We consider D‐A doped CPPs as suitable TADF candidates by evaluating a key condition for maximizing their performance: the lowest singlet and triplet excited‐states must be close enough in energy (ideally resonant or at least separated by less than 0.3 eV) to thus enable a spontaneous or weakly endothermic RISC process. We also emphasize that some other difficulties may arise in practice: (i) this process is possibly gated by dynamical (i.e., conformationally mediated) effects; (ii) experimental suppression of the nonradiative pathways for excited states must be also maximized; (iii) the role played by the whole manifold of lowest‐lying S n and T n excited‐states is still under experimental investigation . Nevertheless, and to the best of our knowledge, this possibility is yet to be explored in cyclic constructs and might be the topic of future research; thus we explore preliminary here the potential use of these molecules without further studying the influence of vibronic, dynamic, environmental, or other related effects.…”

Section: Resultsmentioning

confidence: 99%

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N‐doped cycloparaphenylenes: Tuning electronic properties for applications in thermally activated delayed fluorescence

Graham

Moral²,

Muccioli

et al. 2017

Int J of Quantum Chemistry

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We theoretically characterize a series of substituted cycloparaphenylene nanohoops to study the effect of incorporating an electron-withdrawing group into their cyclic structure. We systematically vary the nature, position, and number of nitrogen-containing acceptor groups in both neutral (pyridine) and charged forms (pyridinium and methylpyridinium) to provide insights into how this functionalization affects the structural, electronic, and optical properties of these systems. We focus also on the singlet-triplet energy difference, with low values found, which might pave the way to further applications in the field of devices for light-emitting applications providing a potential class of TADF-based emitters. K E Y W O R D S density functional theory, donor-acceptor cycloparaphenylenes, optoelectronic properties, TD-DFT, thermally activated delayed fluorescence | I N TR ODU C TI ONOrganic Electronics is a field of rapid growth attracting interest from interdisciplinary domains including electronics & engineering, chemistry, physics, and materials science, not to mention the great commercial interest toward its applications. [1,2] The facile tunability of organic molecules has paved the way for a wealth of organic-based materials to be synthesized with novel key properties. Already, small organic molecules find their place in photovoltaic cells, [3,4] light-emitting transistors, [5][6][7][8][9] and diodes, [10][11][12] to name just a few of these applications. The flexibility of organic materials over inorganic has enabled the birth of the "soft electronics" market, including devices that can twist, bend or mould to any surface or textile. With so many possibilities arising from unique properties of organic molecules, the future of organics appears bright: not only do organic materials promise more innovative technologies but also are far more sustainable (organic molecules are abundant, easily synthesized and potentially Int J Quantum Chem. 2018;118:e25562.

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“…We remind that some of us and others have found before a direct correlation between low

Δ E^{ST}

values and high (low) values of

Δ r

(

ϕ_{S}

), an issue that we would like to further corroborate here. Actually, Figure displays the existing interplay (or correlation) between some of the variables monitored (

Δ E_{v}^{S T}, ϕ_{S} (S_{1})

, and

Δ r (S_{1})

) and indicates how this is indeed the case.…”

Section: Resultssupporting

confidence: 80%

Section: Resultsmentioning

confidence: 99%

N‐doped cycloparaphenylenes: Tuning electronic properties for applications in thermally activated delayed fluorescence

Graham

Moral²,

Muccioli

et al. 2017

Int J of Quantum Chemistry

Self Cite

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“…The normally considered nearly orthogonal molecule of DMAC‐DPS is expected to have a high population (78.4 mol% in vacuum) and the influence of nearly planar molecules will be slight. Moreover, a high energy barrier of 0.13 eV for the nearly orthogonal conformation is enough to further limit the conformational transformation . This explains the good TADF performance reported in DMAC‐DPS.…”

Section: Physical Properties Of Molecules In This Workmentioning

confidence: 96%

Avoiding Energy Loss on TADF Emitters: Controlling the Dual Conformations of D–A Structure Molecules Based on the Pseudoplanar Segments

et al. 2017

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The recent introduction of thermally activated delayed fluorescence (TADF) emitters is regarded as an important breakthrough for the development of high efficiency organic light-emitting devices (OLEDs). The planar D and A groups are generally used to construct TADF emitters for their rigid structure and large steric hindrance. In this work, it is shown that many frequently used nonaromatic (noncontinuous conjugation or without satisfying Hückel's rule) planar segments, such as 9,9-dimethyl-9,10-dihydroacridine, are actually pseudoplanar segments and have two possible conformations-a planar form and a crooked form. Molecules constructed from pseudoplanar segments can thus have two corresponding conformations. Their existence can have significant impact on the performance of many TADF emitters. Two design strategies are presented for addressing the problem by either (1) increasing the rigidity of these groups to suppress its crooked form or (2) increasing the steric hindrance of the linked group to minimize energy of the emitters with the highly twisted form. Following these strategies, two new emitters are synthesized accordingly and successfully applied in OLEDs demonstrating high external quantum efficiencies (20.2% and 18.3%).

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“…[1,14] To achieve such small ΔE ST values, molecules consisting of donor and acceptor moieties are considered and a precise linkage between them is used to reduce the electronic exchange interactions via formation of twisted donor-acceptor conformations. [15][16][17][18][19] Recently developed TADF systems made of an acceptor such as triazine, [8,[20][21][22][23][24][25][26][27] benzophenone, [28,29] or diphenylsulfone [3,30,31] coupled with a donor like an acridane [25,30] or carbazole [9,22,27,28,32] derivative have small ΔE ST , high photoluminescence quantum yield (PLQY), and short delayed fluorescence lifetimes.…”

Section: Introductionmentioning

confidence: 99%

Suppression of Concentration Quenching in Ortho‐Substituted Thermally Activated Delayed Fluorescence Emitters

Abroshan

Cho

Coropceanu

et al. 2019

Advcd Theory and Sims

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Thermally activated delayed fluorescence (TADF) emitters are typically embedded at low concentrations in a host matrix to suppress emission quenching. However, recent studies indicate that TADF compounds such as the oBFCzTrz emitter (5‐(2‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl)phenyl)‐5H‐benzofuro[3,2‐c]carbazole) display insignificant concentration quenching dependence. To understand the origin of this beneficial behavior, the morphology, dynamics, electronic properties, and charge transport and energy transfer in a neat film of the oBFCzTrz emitter are characterized via molecular dynamic simulations combined with density functional theory calculations. The emissive layer shows glassy behavior at room temperature with the twisted configurations of the emitter molecules allowing for intramolecular donor–acceptor interactions, but disfavoring intermolecular π–π stacking, which suppresses the formation of intermolecular aggregate states. As a result, the electronic structure and luminescence of oBFCzTrz are not significantly altered by intermolecular interactions. The calculated diffusion lengths of the singlet and triplet excitons are small enough that there occurs no substantial concentration quenching effect. Overall, the design of new TADF emitters with structural motifs similar to those of oBFCzTrz offers potential to develop efficient organic light‐emitting diode devices in which the emissive layers are entirely composed of TADF molecules without the need for a host component.

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Dynamic nature of excited states of donor–acceptor TADF materials for OLEDs: how theory can reveal structure–property relationships

Abstract: In a theoretical study, we characterized the nature of the key excited states involved in the TADF process of donor–acceptor compounds and showed that light emission is enhanced by dynamic fluctuations of the donor–acceptor torsion resulting from flat torsional potentials.

Cited by 121 publications

References 65 publications

N‐doped cycloparaphenylenes: Tuning electronic properties for applications in thermally activated delayed fluorescence

N‐doped cycloparaphenylenes: Tuning electronic properties for applications in thermally activated delayed fluorescence

Avoiding Energy Loss on TADF Emitters: Controlling the Dual Conformations of D–A Structure Molecules Based on the Pseudoplanar Segments

Suppression of Concentration Quenching in Ortho‐Substituted Thermally Activated Delayed Fluorescence Emitters

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