Synthesis and Characterization of a Highly Reducing Neutral “Extended Viologen” and the Isostructural Hydrocarbon 4,4‘ ‘‘ ‘-Di-<i>n</i>-octyl-<i>p</i>-quaterphenyl

Porter, William A.; Vaid, Thomas P.; Rheingold, Arnold L.

doi:10.1021/ja053084q

Cited by 154 publications

(107 citation statements)

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“…Although there are numerous examples of "extended viologens" in the literature (19)(20)(21)(22)(23)(24)(25) where their electrochemical behavior and/or propensity for electron transfer has been investigated as a result of chemical or structural modifications, there are no examples to our knowledge where IET has been investigated in the context of mechanically interlocked molecules (MIMs). The design of the bistable [2]rotaxane R 6þ ( Fig.…”

Section: Resultsmentioning

confidence: 99%

Mechanically induced intramolecular electron transfer in a mixed-valence molecular shuttle

Barnes

Fahrenbach

Dyar

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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The kinetics and thermodynamics of intramolecular electron transfer (IET) can be subjected to redox control in a bistable [2]rotaxane comprised of a dumbbell component containing an electron-rich 1,5-dioxynaphthalene (DNP) unit and an electron-poor phenylenebridged bipyridinium (P-BIPY 2þ ) unit and a cyclobis (paraquatp-phenylene) (CBPQT 4þ ) ring component. The [2]rotaxane exists in the ground-state co-conformation (GSCC) wherein the CBPQT 4þ ring encircles the DNP unit. Reduction of the CBPQT 4þ leads to the CBPQT 2ð•þÞ diradical dication while the P-BIPY 2þ unit is reduced to its P-BIPY •þ radical cation. A radical-state co-conformation (RSCC) results from movement of the CBPQT 2ð•þÞ ring along the dumbbell to surround the P-BIPY •þ unit. This shuttling event induces IET to occur between the pyridinium redox centers of the P-BIPY •þ unit, a property which is absent between these redox centers in the free dumbbell and in the 1∶1 complex formed between the CBPQT 2ð•þÞ ring and the radical cation of methyl-phenylene-viologen (MPV •þ ). Using electron paramagnetic resonance (EPR) spectroscopy, the process of IET was investigated by monitoring the line broadening at varying temperatures and determining the rate constant (k ET ¼ 1.33 × 10 7 s −1 ) and activation energy (ΔG ‡ ¼ 1.01 kcal mol −1 ) for electron transfer. These values were compared to the corresponding values predicted, using the optical absorption spectra and Marcus-Hush theory.T he simplest organic intervalence compounds consist (1) of two redox centers (X) which are connected by a covalent bridge (b) wherein the two centers possess oxidation states that range from being equal ( nþ0.5 X − b − X nþ0.5 ) to differing by as much as one unit ( n X − b − X nþ1 ). According to the Robin-Day classification (2), there are three main types of organic compounds, which can be defined by the degree of the electronic coupling element, H, that exists between the two interacting redox centers. Compounds that exhibit low electronic coupling between each X redox center have localized charges and exhibit no intramolecular electron transfer (IET) are classified as Class I systems ( n X − b − X nþ1 , H ¼ 0), whereas those that possess a strong electronic coupling between X redox centers and undergo complete delocalization of charge and fast IET are considered Class III systems ( nþ0.5 X − b − X nþ0.5 , H ≫ 0). In between these two classifications lie Class II systems, where the electronic coupling between X redox centers is moderate, leading to a mixture of charge between each unit as well as a measurable IET event.In the 1960s, Marcus (3-6) developed a theory for electron transfer in bridged transition metal-coordinated complexes by identifying the reorganizational energy, λ, required for solvent polarization and subsequent electron transfer between two metal centers. Shortly thereafter, Hush (7-9) proposed a theoretical method that could be applied to Class II intervalence compounds by focusing on the low-energy intervalence charge transfer (IT) bands in optical abso...

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Section: Resultsmentioning

confidence: 99%

Mechanically induced intramolecular electron transfer in a mixed-valence molecular shuttle

Barnes

Fahrenbach

Dyar

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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“…Whether 5 exists as 5a or 5c is not entirely settled. The compound did not afford a well-defined NMR spectrum that would characterize a closed-shell structure, 11 indicating that it might be a diradical, although no EPR evidence for radical character was seen. The second 20 indication of a reactivity limit related to the imidazole-derived compounds 7, 9-12.…”

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confidence: 99%

“…Compound 3 9 is already aromatic and hence its oxidation does not benefit from aromatization as a driving force, and so it also is not a strong donor of electrons. In 35 contrast, donors 4-8 are all converted into aromatic products upon oxidation [10][11][12][13][14][15][16][17][18][19] and this adds to their strength as reducing agents. To illustrate the aromaticity that arises, the oxidation products of compound 8 are also shown in Figure 1.…”

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confidence: 99%

“…Molecule 5a features a number of rings, all of which could 10 become aromatic (5b) on loss of two electrons. 11 However, if such a donor has a sufficient number of linked rings, the aromatic stabilization energy might ensure that the ground-state of 5a will instead be diradical 5c and then the oxidation to 5b by loss of two electrons would only convert the two terminal 15 rings to aromatic rings. Whether 5 exists as 5a or 5c is not entirely settled.…”

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A novel neutral organic electron donor with record half-wave potential

2013

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This version is available at https://strathprints.strath.ac.uk/46029/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the Strathprints administrator: strathprints@strath.ac.ukThe Strathprints institutional repository (https://strathprints.strath.ac.uk) is a digital archive of University of Strathclyde research outputs. It has been developed to disseminate open access research outputs, expose data about those outputs, and enable the management and persistent access to Strathclyde's intellectual output.Journal Name of one and two electrons respectively, also plays an important role in determining the strength of these electron donors. Table 1 compares the oxidation potentials of these compounds with the widely used sulfur-containing electron donor, tetrathiafulvalene (TTF).Among the nitrogen-containing electron-donors, TDAE (1) is the parent compound in the series and the standard by which the others can be judged. 7 Neither 1 nor its oxidized products is aromatic. Compound 2 could be considered anti-aromatic 8 if planar and so its oxidation through loss of two electrons might 30 expect to be strongly driven; however it is quite deformed from planarity and it contains two aromatic pyrrole rings -as a result it is not a strong reducing agent. Compound 3 9 is already aromatic and hence its oxidation does not benefit from aromatization as a driving force, and so it also is not a strong donor of electrons. In 35 contrast, donors 4-8 are all converted into aromatic products upon oxidation [10][11][12][13][14][15][16][17][18][19] and this adds to their strength as reducing agents. To illustrate the aromaticity that arises, the oxidation products of compound 8 are also shown in Figure 1. Loss of one electron leads to radical cation 13 featuring one pyridinium ring, 40 while loss of a second electron affords the aromatic disalt 14. In terms of the applications of these stronger electron donors, benzimidazole-derived 6 converts iodoarenes into aryl radicals, 15 while the stronger donors 7 and 8 reduce the same substrates to aryl anions.12,14 Donors 7 and 8 are also able to reduce 45 arenesulfonamides, 16 Weinreb amides 17 and acyloin derivatives. reducing power is significantly less than that of the strongest metals (e.g. the oxidation potential of Li, E 0 = 3.02 V) 20 and questions arise about whether a limit is bei...

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“…1,4´´´-Diaza-4,1´:4´,1´´:4´´,1´´´-quaterphenylene (PYP2) [203][204][205] Under argon atmosphere 4,4´-biphenyldiboronic acid bis(neopentyl glycol)ester (361 mg, 1.3 mmol), 4-iodpyridine (560 mg, 2.7 mmol, 2.1 equivalents), cesium fluoride (790 mg, 5.2 mmol, 4 equivalents) and tetrakis(triphenylphosphine)-palladium(0) (45 mg, 0.039 mmol, 3 mol%) were dissolved in 60 ml abs. tetrahydrofurane and refluxed for 50 hours.…”

Section: Symmetrically Functionalised Para-quaterphenylenesmentioning

confidence: 99%

Organic Molecular Nanotechnology

Schiek

Balzer

Al‐Shamery

et al. 2008

Small

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Zur Homepage der Dissertation AbstractFormation of needle-like crystals from inorganic as well as from organic semiconductors such as para-phenylenes, α-thiophenes and phenyl-thiophene co-oligomers on dielectric surfaces has attracted increasing interest within the last years. The para-hexaphenylene has proven to be a versatile building block for generating long, parallely aligned organic nanofibers by a self-assembly process on a muscovite mica substrate via sublimation in high vacuum. These nanofibers possess outstanding optical properties like strong, polarised blue fluorescence in high quantum yields after unpolarised excitation with UV light, waveguiding and lasing features. Furthermore, they are chemically and thermically stable and can be easily detached from the growth substrate to serve as key elements in next generation optoelectronic and nanophotonic devices. Owing to their typical height and width on a nanometer scale and length up to one millimeter, the fibers bridge the gap between microscopic and macroscopic dimensions. The morphology of the nanofibers (length, height, width, aspect ratio, bending into rings) is susceptable to process parameters and pretreatment of the substrate. But chemically functionalisation of the molecular building block as key step of this thesis widens the scope of possibilities: Nanoaggregates with tailored morphology and optical properties are generated from designed functionalised molecular building blocks. Functional groups have been implemented at the 1,4´´´-para-positions of p-quaterphenylenes using a non-trivial Suzuki cross-coupling strategy. Symmetrically as well as non-symmetrically functionalised oligomers have been achieved in excellent yields and high purity. Additionally, the synthesis of phenyl-thiophene cooligomers and their acceptability for the nanofiber growth on muscovite mica via organic molecule deposition in high vacuum are presented. The fluorescence peak emission frequency of the nanostructures from the substituted p-quaterphenylenes shifts within the blue depending on the functionalisation. While dimensions are still influenced by the growth parameters, the overall shape (i.e. cross-section) of the aggregates alters significantly with the functional group. Even new properties like nonlinear optical activity are accessible. Due to intrinsic nonzero hyperpolarisability of push-pull functionalised oligomers, the respective nanofibers act as frequency doublers and emit strong second harmonic light after excitation with near infrared femtosecond laser pulses. Note that this design approach is possible while conserving the concept of highly crystalline nanofibers. Thus, a new route of bottom-up nanotechnology is presented starting from organic molecular synthesis towards generating of tailormade organic nanofibers opening new prospects for future nanotechnology. 3 ZusammenfassungDie Bildung von nadelförmigen Kristallen aus anorganischen und organischen Halbleitermolekülen wie zum Beispiel para-Phenylenen, α-Thiophenen und Phenylthiophen Co-oligomeren fa...

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Synthesis and Characterization of a Highly Reducing Neutral “Extended Viologen” and the Isostructural Hydrocarbon 4,4‘ ‘‘ ‘-Di-n-octyl-p-quaterphenyl

Cited by 154 publications

References 37 publications

Mechanically induced intramolecular electron transfer in a mixed-valence molecular shuttle

Mechanically induced intramolecular electron transfer in a mixed-valence molecular shuttle

A novel neutral organic electron donor with record half-wave potential

Organic Molecular Nanotechnology

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