The Three C's of Cethrene

Jurı́ček, Michal

doi:10.2533/chimia.2018.322

Cited by 9 publications

(4 citation statements)

References 11 publications

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“…Helical geometry is also the source of chirality 10 and can create a favorable steric environment for certain intramolecular bond-rearrangement reactions, which, as we shall see, can be translated into a switching function. Recently, we developed 11 the first model system of this type, a C-shaped hydrocarbon cethrene (o- 1 ; Scheme 1, top), composed of seven fused benzenoid rings, five of which form a [5]helicene backbone. By synthesizing the diphenyl derivative o- 1a , we were able to demonstrate 12 its several unique features.…”

Section: Introductionmentioning

confidence: 99%

Dimethylcethrene: A Chiroptical Diradicaloid Photoswitch

et al. 2018

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We describe the synthesis and properties of 13,14-dimethylcethrene, a prototype of a chiral diradicaloid photochemical switch that can be transformed reversibly via conrotatory electrocyclization to its more stable closed form by light (630 nm) or heat and back to its open form by light (365 nm). This system illustrates how the chemical reactivity of a diradicaloid molecule can be translated into a switching function, which alters substantially all electronic parameters, namely, the HOMO–LUMO and the singlet–triplet (ST) energy gaps, and the degree of helical twist. As a result, distinct changes in the optical and chiroptical properties of this system were observed, which allowed us to monitor the switching process by a variety of spectroscopic techniques, including NMR, UV–vis, and CD. In comparison to the previously reported parent molecule cethrene, this system benefits from two methyl substituents installed in the fjord region, which account for the stability of the closed form against oxidation and racemization. The methyl substituents increase the ST energy gap of 13,14-dimethylcethrene by ∼4 kcal mol–1 in comparison to cethrene. Our DFT calculations reveal that the larger ST gap is a result of electronic and geometric effects of the methyl substituents and show the potential of related systems to act as magnetic switches at room temperature.

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Section: Introductionmentioning

confidence: 99%

Dimethylcethrene: A Chiroptical Diradicaloid Photoswitch

et al. 2018

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“…Considering the tendency of [5]helicenes to undergo either light‐ or oxidant‐promoted cyclodehydrogenation resulting in the formation of planar products, we assumed that the appearance of the new signal in the HPLC data could be rationalized by a cyclization process [16–22] . We therefore turned to photostability studies of compound 1 using UV‐visible absorption spectroscopy.…”

Section: Resultsmentioning

confidence: 99%

Synthesis of Helical and Planar Extended‐Phenanthridinium Salts

Hutskalova

Prescimone

Sparr

2021

Helvetica Chimica Acta

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The investigation of new synthetic routes towards positively charged N-heterocycles is of high importance for the further development of medicinal chemistry, functional materials, catalysis and other areas of application. For accessing acridinium dyes, we previously reported an approach based on an aryne-imine-aryne coupling followed by the subsequent oxidation of the acridane intermediates. Herein, we now present an unusual reaction outcome when phenanthryne is used as aryne component. Under optimized conditions, this two-step synthetic methodology led to the formation of a helical tetrabenzophenanthridinium derivative. Furthermore, the susceptibility of this product to photoinduced cyclodehydrogenation was observed, providing a highly fluorescent planar polycyclic aromatic hydrocarbon with a positively charged nitrogen. The photophysical and electrochemical properties of the mesityl-phenyltetrabenzophenanthridinium tetrafluoroborate were also determined.

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“…6,[28][29][30] In contrast, the current research is largely focused on the properties of extended diradicaloids, with efforts being made to suppress 17,[30][31][32] their reactivity in order to obtain stable or persistent systems. A few recent reports indicate, however, that the reactivity of "unchained" diradicaloids, often regarded as an undesired or a decomposition feature, can be utilized to create function 25,[33][34][35][36][37] , develop new methods 38,39 , and deepen our chemical concepts 40,41 . Scheme 1. π-Radical Reactivity Overview a a (Top) Decomposition pathway of phenalenyl (PLY) to peropyrene (PP) via 6π EC of biphenalenylidene (BPLY).…”

Section: Introductionmentioning

confidence: 99%

Nonacethrene Unchained: A Cascade to Chiral Contorted Conjugated Hydrocarbon with Two sp3-Defects

Čavlović

Häußinger

Blacque

et al. 2022

Preprint

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A dihydro precursor of helical diradicaloid nonacethrene undergoes a reaction cascade triggered by an oxidant to a chiral contorted polycyclic aromatic hydrocarbon named hypercethrene. In this ten-electron-oxidation process, four σ bonds, one π bond, and three six-membered rings are formed in a reaction sequence of up to nine steps to yield a 72-carbon-atom warped framework, comprising two configurationally locked [7]helicene units, fluorescent peropyrene unit, and two precisely installed sp3-defects.The key intermediate in this cascade is a closed nonacethrene derivative with one quaternary center, presumably formed via an electrocyclic ring closure of nonacethrene, which— when activated by oxidation—undergoes an oxidative dimerization of phenalenyl to peropyrene. By controlling the amount oxidant used, two intermediates and one side product could be isolated and fully characterized, including single-crystal X-ray diffraction analysis, and one intermediate was detected by electron paramagnetic resonance spectroscopy. In concert with density functional theory calculations, these intermediates support the proposed reaction mechanism. Compared to peropyrene, the absorption and emission of hypercethrene are slightly red-shifted on account of extended conjugation and the fluorescence quantum yield of 0.45 is decreased by a factor of ~2. Enantiomerically enriched hypercethrene displays circularly polarized luminescence with a CPL brightness value of 8.3 M–1cm–1. This unexpected reaction cascade demonstrates that the reactivity of “unchained”diradicaloid compounds, which is typically considered an undesired feature, can be well-defined and employed as a useful, step-economic synthetic tool toward novel carbon nanostructures.

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The Three C's of Cethrene

Cited by 9 publications

References 11 publications

Dimethylcethrene: A Chiroptical Diradicaloid Photoswitch

Dimethylcethrene: A Chiroptical Diradicaloid Photoswitch

Synthesis of Helical and Planar Extended‐Phenanthridinium Salts

Nonacethrene Unchained: A Cascade to Chiral Contorted Conjugated Hydrocarbon with Two sp3-Defects

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