Violation of Hund’s rule in molecules: Predicting the excited-state energy inversion by TD-DFT with double-hybrid methods

Sancho‐García, Juan Carlos; Brémond, Éric; Ricci, Gaetano; Pérez-Jiménez, Ángel J.; Olivier, Yoann; Adamo, Carlo

doi:10.1063/5.0076545

Cited by 37 publications

(55 citation statements)

References 105 publications

(107 reference statements)

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“…Therefore, a reliable and cost-effective method for prediction for MR-TADF compounds is desirable, for example, the double-hybrid functionals, as revealed in the recent benchmark study on Hund's-rule-violating molecules. [45] Most compounds obey Hund's multiplicity rule, where their T 1 states lie below their S 1 states. Up to now, only few compounds violate Hund's rule, [46] showing a negative ΔE ST .…”

Section: Design Of Thermally-activated Delayed Fluorescence Emittersmentioning

confidence: 99%

“…[46] Fortunately, a recent benchmark study by Sancho-Garcia et al showed that TD-DFT with double-hybrid functionals can give the correct negative feature of ΔE ST . [45] These methods can thus be used in computational high-throughput screening to further increase the number of Hund's-rule-violating molecules. The electron is more stable in the phase with lower electron affinity (larger negative energy values) and the hole is more stable in the material with the higher ionization energy.…”

Section: Design Of Thermally-activated Delayed Fluorescence Emittersmentioning

confidence: 99%

“…Therefore, a reliable and cost‐effective method for prediction for MR‐TADF compounds is desirable, for example, the double‐hybrid functionals, as revealed in the recent benchmark study on Hund's‐rule‐violating molecules. [ 45 ]…”

Section: Design Of Thermally‐activated Delayed Fluorescence Emittersmentioning

confidence: 99%

“…showed that TD‐DFT with double‐hybrid functionals can give the correct negative feature of Δ E ST . [ 45 ] These methods can thus be used in computational high‐throughput screening to further increase the number of Hund's‐rule‐violating molecules.…”

Section: Design Of Thermally‐activated Delayed Fluorescence Emittersmentioning

confidence: 99%

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Virtual Screening for Organic Solar Cells and Light Emitting Diodes

et al. 2022

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We dedicate this contribution to Klaus Müllen on the occasion of his 75th birthday. He advanced the synthesis and application of organic electronic compounds in an internationally leading position for many years and always challenged theory to provide a better understanding.The field of organic semiconductors is multifaceted and the potentially suitable molecular compounds are very diverse. Representative examples include discotic liquid crystals, dye-sensitized solar cells, conjugated polymers, and graphene-based low-dimensional materials. This huge variety not only represents enormous challenges for synthesis but also for theory, which aims at a comprehensive understanding and structuring of the plethora of possible compounds. Eventually computational methods should point to new, better materials, which have not yet been synthesized. In this perspective, it is shown that the answer to this question rests upon the delicate balance between computational efficiency and accuracy of the methods used in the virtual screening. To illustrate the fundamentals of virtual screening, chemical design of non-fullerene acceptors, thermally activated delayed fluorescence emitters, and nanographenes are discussed.

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Section: Design Of Thermally-activated Delayed Fluorescence Emittersmentioning

confidence: 99%

Section: Design Of Thermally-activated Delayed Fluorescence Emittersmentioning

confidence: 99%

Section: Design Of Thermally‐activated Delayed Fluorescence Emittersmentioning

confidence: 99%

Section: Design Of Thermally‐activated Delayed Fluorescence Emittersmentioning

confidence: 99%

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Virtual Screening for Organic Solar Cells and Light Emitting Diodes

et al. 2022

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“…Shortly speaking, although this method is able to provide negative values for ∆E ST , the results appear to be affected by a systematic error. The use of double-hybrid functionals has been recently and more systematically examined [52], with some of the models assessed being promising enough to display accurate individual excitation energies: we thus refer the reader to that study for further information and confirmation about the key role played by double excitations into the final values.…”

Section: Td-dft Calculationsmentioning

confidence: 99%

Organic Emitters Showing Excited-States Energy Inversion: An Assessment of MC-PDFT and Correlation Energy Functionals Beyond TD-DFT

Sancho‐García

San‐Fabián

2022

Computation

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The lowest-energy singlet (S1) and triplet (T1) excited states of organic conjugated chromophores are known to be accurately calculated by modern wavefunction and Time-Dependent Density Functional Theory (TD-DFT) methods, with the accuracy of the latter heavily relying on the exchange-correlation functional employed. However, there are challenging cases for which this cannot be the case, due to the fact that those excited states are not exclusively formed by single excitations and/or are affected by marked correlation effects, and thus TD-DFT might fall short. We will tackle here a set of molecules belonging to the azaphenalene family, for which research recently documented an inversion of the relative energy of S1 and T1 excited states giving rise to a negative energy difference (ΔEST) between them and, thereby, contrary to most of the systems thus far treated by TD-DFT. Since methods going beyond standard TD-DFT are not extensively applied to excited-state calculations and considering how challenging this case is for the molecules investigated, we will prospectively employ here a set of non-standard methods (Multi-Configurational Pair Density Functional Theory or MC-PDFT) and correlation functionals (i.e., Lie–Clementi and Colle–Salvetti) relying not only on the electronic density but also on some modifications considering the intricate electronic structure of these systems.

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Symmetry‐Induced Singlet‐Triplet Inversions in Non‐Alternant Hydrocarbons**

2023

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Molecules with inversion of the singlet and triplet excited‐state energies are highly promising for the development of organic light‐emitting diodes (OLEDs). To date, azaphenalenes are the only class of molecules where these inversions have been identified. Here, we screen a curated database of organic crystal structures to identify existing compounds for violations of Hund's rule in the lowest excited states. We identify two further classes with this behavior. The first, a class of zwitterions, has limited relevance to molecular emitters as the singlet‐triplet inversions occur in the third excited singlet state. The second class consists of two D2h‐symmetry non‐alternant hydrocarbons, a fused azulene dimer and a bicalicene, whose lowest excited singlet states violate Hund's rule. Due to the connectivity of the polycyclic structure, they achieve this symmetry through aromatic stabilization. These hydrocarbons show promise as the next generation of building blocks for OLED emitters.

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Violation of Hund’s rule in molecules: Predicting the excited-state energy inversion by TD-DFT with double-hybrid methods

Cited by 37 publications

References 105 publications

Virtual Screening for Organic Solar Cells and Light Emitting Diodes

Virtual Screening for Organic Solar Cells and Light Emitting Diodes

Organic Emitters Showing Excited-States Energy Inversion: An Assessment of MC-PDFT and Correlation Energy Functionals Beyond TD-DFT

Symmetry‐Induced Singlet‐Triplet Inversions in Non‐Alternant Hydrocarbons**

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