Paradise Lost—π-Electron Conjugation in Homologs and Derivatives of Perylene

Gutman, Ivan; Radenković, Slavko

doi:10.1007/978-3-319-29022-5_11

Cited by 5 publications

(3 citation statements)

References 130 publications

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“…The pseudo-π maps for zethrene were not noticeably improved by repeating the calculation in tests at the ab initio CHF or DFT levels. Problems with zethrene and similar molecules have been noted before, and are often attributed to incipient radical character, , implying the need for a multireference treatment. Similar difficulties have been noted in treatments of ballistic conduction, where currents in some conjugated molecules can be badly misrepresented in single-reference treatments .…”

Section: Resultsmentioning

confidence: 83%

Ring-Current Maps for Benzenoids: Comparisons, Contradictions, and a Versatile Combinatorial Model

et al. 2020

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As a key diagnostic property of benzenoids and other polycyclic hydrocarbons, induced ring current has inspired diverse approaches for calculation, modeling, and interpretation. Grid-based methods include the ipsocentric ab initio calculation of current maps, and its surrogate, the pseudo-π model. Graph-based models include a family of conjugated-circuit (CC) models and the molecular-orbital Huckel-London (HL) model. To assess competing claims for physical relevance of derived current maps for benzenoids, a protocol for graph-reduction and comparison was devised. Graph reduction of pseudo-π grid maps highlights their overall similarity to HL maps, but also reveals systematic differences. These are ascribed to unavoidable pseudo-π proximity limitations for benzenoids with short nonbonded distances, and to poor continuity of pseudo-π current for classes of benzenoids with fixed bonds, where single-reference methods can be unreliable. Comparison between graph-based approaches shows that the published CC models all shadow HL maps reasonably well for most benzenoids (as judged by L 1 -, L 2 -, and L ∞ -error norms on scaled bond currents), though all exhibit physically implausible currents for systems with fixed bonds. These comparisons inspire a new combinatorial model (Model W) based on cycle decomposition of current, taking into account the two terms of lowest order that occur in the characteristic polynomial. This improves on all pure-CC models within their range of applicability, giving excellent adherence to HL maps for all Kekulean benzenoids, including those with fixed bonds (halving the rms discrepancy against scaled HL bond currents, from 11% in the best CC model, to 5% for the set of 18 360 Kekulean benzenoids on up to 10 hexagonal rings). Model W also has excellent performance for open-shell systems, where currents cannot be described at all by pure CC models (4% rms discrepancy against scaled HL bond currents for the 20112 non-Kekulean benzenoids on up to 10 hexagonal rings). Consideration of largest and next-to-largest matchings is a useful strategy for modeling and interpretation of currents in Kekulean and non-Kekulean benzenoids (nanographenes).

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Section: Resultsmentioning

confidence: 83%

Ring-Current Maps for Benzenoids: Comparisons, Contradictions, and a Versatile Combinatorial Model

et al. 2020

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“…A similar, and more pronounced, phenomenon regarding strong topological ring-currents in the centers of larger structures was noted in ref , in the middle regions of large, fully benzenoid hydrocarbons. It is in any case clear that in the five-membered rings of angularly naphtho-annelated fluoranthene derivatives there can be a significant extent of cyclic π-electron conjugation (albeitwhen judged by the criteria of topological ring-currentssmaller than that encountered in the six-membered rings) that cannot be anticipated from Kekulé structures (according to which the five-membered ring is an “empty” ,,, ring).…”

Section: Trends In the Topological Ring-currents And Comparison With ...mentioning

confidence: 99%

Assessing the Extent of π-Electron Delocalization in Naphtho-Annelated Fluoranthenes by Means of Topological Ring-Currents

Dickens

Mallion²,

Radenković

2019

J. Phys. Chem. A

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The extent of π-electron delocalization in the fivemembered rings of 14 naphtho-annelated fluoranthenes has recently been assessed by means of several approaches, including application of the following indices: the energy effect (ef), bond resonanceenergy (BRE), multicenter delocalization-energies (MCI), the index arising from the harmonic-oscillator model of aromaticity (HOMA), and nucleus-independent chemical shifts (NICS). The calculated Huckel−London−Pople−McWeeny (HLPM) ("topological") ring-current intensities (TRC) for the five-membered rings of these same structures are here compared with the above-named indices in order to assess how well TRC parallels these other criteria. The indices ef and BRE are the ones that correlate best with TRC, and it is suggested that this is because all three approaches are founded on the Huckel model. TRC does not, however, confirm the proposal that cyclic delocalization in the five-membered rings can be greater than in any of the six-membered rings in this series of conjugated systems. Certain ostensible shortcomings of the NICS approach are discussed, and some doubts are emphasized regarding the legitimacy of associating "ring currents" with "aromaticity".

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“…Conjugated-circuit models have an attractive simplicity, but have crucial drawbacks for non-Kekulean systems, where they predict zero current, and for Kekulean systems with fixed bonds, where they predict 'dead zones' of vanishing current [43][44][45]. The current maps from conjugated-circuit models can be seen as approximate versions of HL current maps in which only certain 'important' cycles have been selected and given model-dependent weightings.…”

Section: Introductionmentioning

confidence: 99%

Partitioning Hückel–London Currents into Cycle Contributions

2021

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Ring-current maps give a direct pictorial representation of molecular aromaticity. They can be computed at levels ranging from empirical to full ab initio and DFT. For benzenoid hydrocarbons, Hückel–London (HL) theory gives a remarkably good qualitative picture of overall current patterns, and a useful basis for their interpretation. This paper describes an implemention of Aihara’s algorithm for computing HL currents for a benzenoid (for example) by partitioning total current into its constituent cycle currents. The Aihara approach can be used as an alternative way of calculating Hückel–London current maps, but more significantly as a tool for analysing other empirical models of induced current based on conjugated circuits. We outline an application where examination of cycle contributions to HL total current led to a simple graph-theoretical approach for cycle currents, which gives a better approximation to the HL currents for Kekulean benzenoids than any of the existing conjugated-circuit models, and unlike these models it also gives predictions of the HL currents in non-Kekulean benzenoids that are of similar quality.

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Paradise Lost—π-Electron Conjugation in Homologs and Derivatives of Perylene

Cited by 5 publications

References 130 publications

Ring-Current Maps for Benzenoids: Comparisons, Contradictions, and a Versatile Combinatorial Model

Ring-Current Maps for Benzenoids: Comparisons, Contradictions, and a Versatile Combinatorial Model

Assessing the Extent of π-Electron Delocalization in Naphtho-Annelated Fluoranthenes by Means of Topological Ring-Currents

Partitioning Hückel–London Currents into Cycle Contributions

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