Structural effects on the spin distribution anomaly of viologens

Sariciftci, Niyazi Serdar; Werner, A.; Mehring, M.

doi:10.1080/00268979200100971

Cited by 3 publications

(8 citation statements)

References 9 publications

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“…[34] This spectrum can be simulated [18] on the basis of complete electron delocalization around the bipyridinium nucleus, including the aza N atoms and the methyl groups. [35] This behavior is consistent with a high degree of resonance stabilization of the radical [36] and, in particular, confirms that the central C À C bond acquires some degree of double-bond character, with the radical moving towards a planar geometry.…”

Section: Resultssupporting

confidence: 67%

“…For MV 2 + , successive electron additions occur with reduction potentials of À0. 35 and À0.76 V versus SCE in deoxygenated acetonitrile solution ( Table 2). The difference between these values, which gives access to the comproportionation constant, [33] provides an indirect measure of electron delocalization at the monocation radical stage.…”

Section: Resultsmentioning

confidence: 99%

“…EPR spectroscopy: Several prior studies [34,35] have addressed the EPR properties of the moncation radical derived from the parent viologen MVC + and from viologens bearing different substituents at the aza N atoms. [37] In our work, MVC + was generated by in situ electrochemical reduction in deoxygenated acetonitrile and the EPR spectrum was recorded at room temperature (see Supporting Information), for which the g factor was found to be 2.0031.…”

Section: Spectroelectrochemistrymentioning

confidence: 99%

“…The latter can be divided into protons on the methyl groups (a Me = 0.399 mT) and two equivalent sets, each of four protons, on the aromatic nucleus. On the basis of earlier work [34,35] and INDO calculations, [37] the hyperfine coupling constants for these aryl H atoms can be assigned to the C a (a CH = À0.133 mT) and C b (a CH = À0.157 mT) sites. Calculations made at the INDO level have indicated [26d] that the central torsion angle has a modest effect on the a CH values once f exceeds about 158.…”

Section: Spectroelectrochemistrymentioning

confidence: 99%

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A Spectroscopic Study of the Reduction of Geometrically Restrained Viologens

Benniston¹,

Harriman²,

Li³

et al. 2007

Chemistry A European J

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A small series of N,N'-dimethyl-4,4'-bipyridinium dication derivatives (commonly known as viologens) has been synthesized and fully characterized; a short dialkoxy tether attached at the 3,3'-positions is used to alter the central dihedral angle. These angles were determined by both single-crystal X-ray diffraction and by computational studies made for the dication, radical cation, and neutral species in a solvent reservoir. The dihedral angle derived for the dication controls the first reduction potential, whereas the geometry of the resultant pi-radical cation determines the magnitude of the second reduction potential. The optical absorption spectra recorded for the various species, and especially those of the radical cations, and the EPR spectral parameters of the pi-radical cations also depend on the molecular geometry. In particular, the central dihedral angle influences the spin density distribution around the aromatic nucleus and, by way of comparison to the parent viologen, it has been possible to resolve the angle dependence from the inherent inductive effect of the strap. These results are considered in terms of the degree of electronic communication between the two aromatic rings, as controlled by the length of the tether.

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Section: Resultssupporting

confidence: 67%

Section: Resultsmentioning

confidence: 99%

Section: Spectroelectrochemistrymentioning

confidence: 99%

Section: Spectroelectrochemistrymentioning

confidence: 99%

See 2 more Smart Citations

A Spectroscopic Study of the Reduction of Geometrically Restrained Viologens

Benniston¹,

Harriman²,

Li³

et al. 2007

Chemistry A European J

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“…There is, however, a fundamental discrepancy between the theoretical and experimental data which was observed already before, namely the interchange of the values for the ring protons at the viologen molecule [16]. Detailed INDO studies and comparison with results on different substituted viologens show this discrepancy arising from structural distortions in the radical state as discussed in a separate publication [22]. Otherwise the INDO calculations do reproduce the trend that the largest hyperfine interactions is due to the methyl group caused by hyperconjugation.…”

Section: Discussionmentioning

confidence: 80%

On the spin distribution in bridged anthracene-viologen molecules: an electron-nuclear double resonance study

et al. 1992

Self Cite

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Studies on the spin distribution in the radical state of anthracene-a bridgeviologen supermolecules with different bridge units are reported. Electronnuclear double resonance experiments (ENDOR) were performed on electrochemically reduced molecules. Proton hyperfine coupling constants at different molecular sites were obtained and are discussed in detail. The experimentally determined values are compared with quantum chemical calculations of the INDO type. The observed spin distribution depends significantly on the type of the bridging unit. The relevance of the spin distribution for electron transfer in donor-bridge-acceptor molecular complexes is discussed.

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Geostatistics for assessing the efficiency of a distributed physically‐based water quality model: application to nitrate in the Seine River

Polus¹,

Flipo²,

Fouquet³

et al. 2010

Hydrological Processes

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International audienceThis article shows how geostatistics can be used to reduce distributed physically based model (DPBM) uncertainties when assessing nitrate concentrations along a 250-km stretch of the Seine River. First of all, co-kriging is used to build a set of boundary conditions (BCs) (inlet concentrations from major tributary rivers) consistent with validation data. It partially addresses the issues of errors in data used as model input and errors in data to be compared with model outputs. Then the analysis of temporal variograms (simple variograms of observed and simulated concentrations, and their cross-variogram) reveals a clear mismatch between simulated and observed values that was not detected by classical objective functions [root mean squared error (RMSE), etc.]. Variograms appear to include three components representing three different time scales: sub-weekly, monthly and annual scales. Mismatches between simulated and observed values are analysed as (i) wrong quantification of inputs to the river (especially during the rainy period: combined sewer overflow (CSO), waste water treatment plant (WWTP) and tributary contributions to the nitrate fluxes in the Seine River) and (ii) wrong description of physical processes within the river. Finally, the modelling of simple and cross-variograms appears to be a sensitive analysis tool which can be used to describe and reduce modelling uncertaintie

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Structural effects on the spin distribution anomaly of viologens

Cited by 3 publications

References 9 publications

A Spectroscopic Study of the Reduction of Geometrically Restrained Viologens

A Spectroscopic Study of the Reduction of Geometrically Restrained Viologens

On the spin distribution in bridged anthracene-viologen molecules: an electron-nuclear double resonance study

Geostatistics for assessing the efficiency of a distributed physically‐based water quality model: application to nitrate in the Seine River

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