Violation of Hund's rule in the lowest excited singlet-triplet pairs of dicyclohepta[cd,gh]pentalene and dicyclopenta[ef,kl]heptalene

Toyota, Azumao

doi:10.1007/bf00527144

Cited by 24 publications

(31 citation statements)

References 20 publications

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“…A different type of exception appears when bonding orbitals are vacant, or antibonding orbitals are occupied as noted for the first time by Bochvar, Stankevich, and Tutkevich for compound 21, 41 and studied later by several research groups. [4][5][6][7][8][9][10][11][12] For benzenoids, the set of all possible Kekule ´structures, as well as the Fries and Clar structures graphically convey information about the distribution of π-electrons. (One may recall that a Fries structure of an aromatic benzenoid has the maximum possible rings with three double bonds, e.g.…”

Section: Aromaticity Kekule ä Fries and Clar Structures Partition Of...mentioning

confidence: 99%

“…Whereas the previous Parts of this series discussed only aromatic polycyclic benzenoids, [1][2][3] in the present paper we include also antiaromatic systems such as pentalene (1) and heptalene (3), as well as systems with special HOMO-LUMO situations such as 21, 22, 75, 76, 181-187. [4][5][6][7][8][9][10][11][12] There exist many monographs on the aromaticity of benzenoid compounds that have been cited in previous Parts of this series. The problems connected with the aromaticity of nonbenzenoid nonalternant hydrocarbons were reviewed in fewer monographs and reviews.…”

Section: Introductionmentioning

confidence: 99%

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Partitioning of π-Electrons in Rings of Polycyclic Conjugated Hydrocarbons. 5. Nonalternant Compounds

Balaban

Randić

2004

J. Chem. Inf. Comput. Sci.

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All possible nonalternant hydrocarbons with a total of two, three, or four 5-, 6-, and 7-membered rings have been examined for the partition of their pi-electrons by averaging over all Kekulé structures (considered to contribute equally to the electron distribution) the pi-electrons in each ring in accordance to the rules introduced earlier: for each double bond shared with another ring one pi-electron is taken into account, and for double bonds that are not shared two pi-electrons are added. The trends observed for the partitions are discussed, and a comprehensive bibliography is provided as Supporting Information for all such systems, including both experimental and theoretical published data.

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Section: Aromaticity Kekule ä Fries and Clar Structures Partition Of...mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Partitioning of π-Electrons in Rings of Polycyclic Conjugated Hydrocarbons. 5. Nonalternant Compounds

Balaban

Randić

2004

J. Chem. Inf. Comput. Sci.

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“…Very few, i.e. on the order of 10, organic INVEST molecules were predicted on the basis of computations alone 2,13,14 with little to no experimental evidence, 15,16 and, as far as we know, no inorganic INVEST molecule is known to date. Besides inherently inverted molecules, it has been shown in recent years that the influence of the environment can also make the gap negative, 17 for instance in exciplexes, 18 through strong light-matter coupling in microcavities, 19 and polarizable environments.…”

Section: Introductionmentioning

confidence: 99%

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

Pollice

Friederich²,

Lavigne³

et al. 2020

Preprint

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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.

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“…Here, we have identified the singlet-triplet inversion in COLDEM through high-throughput screening of experimental molecules. However, COLDEM and pentalene were among several conjugated hydrocarbons proposed by Toyota and coworkers as possible Hund's rule violations in the 1980s, [49][50][51] which have been overlooked in the recent literature. Given that this prior work was based on symmetry analysis and HF/ STO-3G level calculations with a simplified configuration interaction scheme, we surveyed all proposed molecules from this earlier work at the EOM-CCSD/aug-cc-pVDZ level (Figure S16).…”

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confidence: 99%

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 the lowest excited singlet-triplet pairs of dicyclohepta[cd,gh]pentalene and dicyclopenta[ef,kl]heptalene

Cited by 24 publications

References 20 publications

Partitioning of π-Electrons in Rings of Polycyclic Conjugated Hydrocarbons. 5. Nonalternant Compounds

Partitioning of π-Electrons in Rings of Polycyclic Conjugated Hydrocarbons. 5. Nonalternant Compounds

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

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

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