Dendrimers with a 4,4′-bipyridinium core and electron-donor branches. Electrochemical and spectroscopic properties

Ceroni, Paola; Vicinelli, Veronica; Maestri, Matteo; Balzani, Vincenzo; Müller, Walter M.; Müller, Ute; Hahn, Uwe; Osswald, Friederike; Vögtle, Fritz

doi:10.1039/b104131m

Cited by 53 publications

(47 citation statements)

References 23 publications

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“…[9][10][11][12] For comparison purposes, we have also investigated the behavior of the simple viologen species A 1 2 + and A' 1 2 + , as reference compounds for the viologen units of the polyviologen dendrimers, and of compound S, as a reference for the tetraarylmethane end groups (Scheme 1).…”

Section: Introductionmentioning

confidence: 99%

Complete Charge Pooling is Prevented in Viologen‐Based Dendrimers by Self‐Protection

Marchioni

Venturi

Ceroni

et al. 2004

Chemistry A European J

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We have investigated the electrochemical behavior, and chemical and photosensitized reduction of two dendrimers based on a 1,3,5-trisubstituted benzenoid core, which contain 9 and 21 4,4'-bipyridinium (usually called viologen) units, respectively, in their branches and are terminated with tetraarylmethane groups. For comparison purposes, the behavior of reference compounds that contain a single viologen unit have also been investigated. We have found that only part of the viologen units can be reduced in the dendrimer species. For the larger dendrimer, the number of reducible viologens (out of the 21 present) is 14 in electrochemical experiments (in MeCN), 9 on reduction with bis(benzene)chromium (in MeCN), and 13 by photoinduced electron transfer with 9-methylanthracene as a photosensitizer and triethanolamine as a sacrificial reductant in CH2Cl2. The reduced viologen units undergo partial dimerization. The photochemical experiments have shown that only monomeric, one-electron-reduced viologen units are formed at the beginning of the irradiation, followed by dimer formation, until a photostationary state is reached that contains 40 % nonreduced, 33 % monomeric reduced, and 27 % reduced units associated in the dimeric form. The results suggest that, upon reduction of a fraction of the viologen units, the dendrimer structure shrinks, with the result that the bulky terminal groups protect other viologen units from being reduced.

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Section: Introductionmentioning

confidence: 99%

Complete Charge Pooling is Prevented in Viologen‐Based Dendrimers by Self‐Protection

Marchioni

Venturi

Ceroni

et al. 2004

Chemistry A European J

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“…1 Functional dendrimers may incorporate redox centers, and potential applications include antennae molecules for light harvesting, sensors, mediators, and artificial biomolecules. Dendrimers with a redox core show no significant inhibition 2 but also shielding (by the branches) 3 and orientation effects (in asymmetric dendrimers) upon the rate of heterogeneous electron transfer. 4 Dendrimers with redox centers in the branches are also well-known.…”

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Redox-Active Star Molecules Incorporating the 4-Benzoylpyridinium Cation: Implications for the Charge Transfer Efficiency along Branches vs Across the Perimeter in Dendrimers

et al. 2004

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Dendrimers are self-repeating globular branched star molecules, whose fractal structure continues to fascinate, challenge, and inspire. 1 Functional dendrimers may incorporate redox centers, and potential applications include antennae molecules for light harvesting, sensors, mediators, and artificial biomolecules. Dendrimers with a redox core show no significant inhibition 2 but also shielding (by the branches) 3 and orientation effects (in asymmetric dendrimers) upon the rate of heterogeneous electron transfer. 4 Dendrimers with redox centers in the branches are also well-known. Using thinlayer-cell electrochemistry, all 21 tetrathiafulvalenes embedded in the branches of a third-generation dendrimer are electrochemically accessible leading to a 42+ cation. 5 Using pulse radiolysis, Fox reported fast electron transfer (e-transfer) between peripheral biphenyls (donors) and a core acceptor (a Ru(II)-complex). 6 On the other hand, Crooks has reported incomplete electrolysis of amido amine dendrimers with a viologen functionalized perimeter, 7 while Amatore and Abruña using ultrafast voltammetry have reported fast e-transfer, despite the 2-nm separation from one another, among the 64 Ru-complexes in the perimeter of a fourth-generation dendrimer adsorbed on a microelectrode; 8 the fast charge propagation was attributed to the branch flexibility.On the basis of those reports, e-transfer across the perimeter of dendrimers should depend on their rigidity, but it is unclear whether it would be more or less efficient than e-transfer along the branches. As these questions have important implications for molecular design, they were investigated with star systems 1-4, serving as models of first-and second-generation redox dendrimers. Cations 1-4 incorporate 4-benzoyl-N-alkylpyridinium (BP), 9 whose redox potential (a) varies along the branches and (b) remains constant at fixed radius. Our strategy was to measure the number of electrons, n 1 , exchanged between 1 and the electrode at different time-scales, and infer how easily charge randomizes across the perimeter of a relatively small, rigid redox star-system. Thus, n 1 was assessed both at a semi-infinite time scale (by bulk electrolysis) and at the cyclic voltammetric (CV) time scale of 0.02-10 V s -1 . Next, the voltammetry of 2-4 was used to assess whether within the same time scale redox centers within the branches are as accessible as redox centers across the perimeter. Figure 1 shows the redox processes of 1 versus decamethylferrocene (dMeFc: internal standard). 10 One-electron-like waves indicate that redox units behave independently of one another. 11 Bulk electrolysis of 1 at -0.85 V vs Ag/AgCl affords n 1 ) 3.01 ( 0.03. The linearity of the Randles-Sevcik plot in inset A shows that the number of redox centers reduced remains unchanged in the time scale of 0.02-10 V s -1 . Within this time-scale, n 1 was determined first by comparing the ratio of the slopes of the Randles-Sevcik plots of 1 and dMeFc with the limiting current ratio obtained in the same solution wi...

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“…The fluorescence of the 1,3-dimethyleneoxybenzene units is completely quenched in the dendrimers. [15] In a solution of 9:1 dichloromethane/acetonitrile, tweezer T shows an irreversible oxidative process at + 1.6 V, whereas no reduction process could be observed in the potential window of the solvent used (up to À2.0 V vs. SCE). The…”

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confidence: 98%

“…2+ dendrimers [15,19] show two one-electron-transfer processes that correspond to the successive reductions of the 4,4'-bipyridinium core: bpy 2+ is shown in Figure 3.…”

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Tweezering the Core of a Dendrimer: A Photophysical and Electrochemical Study

et al. 2005

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Dendrimers with a 4,4′-bipyridinium core and electron-donor branches. Electrochemical and spectroscopic properties

Cited by 53 publications

References 23 publications

Complete Charge Pooling is Prevented in Viologen‐Based Dendrimers by Self‐Protection

Complete Charge Pooling is Prevented in Viologen‐Based Dendrimers by Self‐Protection

Redox-Active Star Molecules Incorporating the 4-Benzoylpyridinium Cation: Implications for the Charge Transfer Efficiency along Branches vs Across the Perimeter in Dendrimers

Tweezering the Core of a Dendrimer: A Photophysical and Electrochemical Study

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