Bipyridinium dication

Derivatives of 4,4 -bipyridinium dication in electrochromic techniques 96CLY135. 

Conclusion. Our major conclusion is that surfactant bipyridinium dications do not remain at a fixed location within a mercaptan monolayer. In order to control the spacing and orientation of the bipyridiniums in the monolayer, it will be necessary to anchor them within the monolayer or to the electrode. We are currently pursuing that goal by synthesizing a bipyridinium with a terminal mercaptan. 

Figure B. Pictorial representation of the self-assembly of pseudorotaxa-nes based on (a) charge-transfer and C-H—O hydrogen-bonding interactions between 1,1 -diben-zyl-4,4 -bipyridinium dication and 1,5-dinaphtho[38] crown-10 (1/5DN38C10), and (b) hydrogen-bonding interactions between dibenzyl ammonium ion and dibenzo[24]crown-8 (DB24C8). A possible route towards the synthesis of rotaxanes and catenanes is also schematized.

The high affinity of ammonium cations for tetra-bridged phosphorus(IV) P=0 cavitands was used to complex bis-ammonium guests. The highly insoluble NjAT-dimethyl-bipyridinium dication [paraquat " ] was readily dissolved in chloroform solution in presence of 12b in a 2 1 host-guest ratio. 

Although the high resolution X-ray crystal analysis of 4,4 -bipyridine has not been reported, the crystal structure of 4,4 -bipyridinium chlorocuprate (22) has been discussed. Whereas the dimensions of the 4,4 -bipyridinium dication may have been distorted because of the influence of the bulky metal cation, it is interesting to note that the 4,4 -bipyridinium dication is planar with both pyridine rings lying in the same plane. In metal complexes of the parent 4,4 -bipyridine, however, the pyridine rings may be coplanar or rotated up to 40° with respect to one other. 

Figure 7.4 Electroactive compounds incorporating 4,4 -bipyridinium dications and either one (6) or two (7) thiol groups.

On the basis of these considerations, we designed the bipyridinium derivatives 6 and 7 (Fig. 7.4).27b,c Both incorporate two 4,4 -bipyridinium dications separated by a... 

The immersion of a polycrystalline gold electrode into a chloroform/methanol (2 1, v/v) solution of the tetrachloride salt of 6 (Fig. 7.4) results in the adsorption of this electroactive thiol on the metal surface.270 Consistently, the cyclic voltammogram (Fig. 7.5a), recorded after an immersion time of 24 h and extensive rinsing of the electrode surface, shows the reversible reduction of the bipyridinium dications to the corresponding radical cations. In addition, zp increases linearly with v (Fig. 7.6a),... 

Figure 7.9 Electrons travel from the electrode to the ruthenium centers through the bipyridinium dications (a), when the gold voltage (V versus Ag/AgCl) matches the reduction potential of the bipyridinium dications, but cannot return from the ruthenium centers to the electrode (b), even when the voltage is lowered below the oxidation potential of the ruthenium centers.

Bipyridinium dications do not absorb in the visible region of the electromagnetic spectrum.28 After their electrochemical reduction to the corresponding radical cations, however, a broad and intense absorption appears across the visible region. The process is fully reversible and the colorless state is regenerated, after the oxidation of the radical cations back to the original dications. In fact, bipyridinium dications are convenient building blocks for the realization of electrochromic materials, as a result of their spectroscopic response to electrochemical inputs. 

To assess the electrochromic response of the bipyridinium dications embedded into multilayers of 7, we envisaged the possibility of assembling these films on optically transparent platinum electrodes.27d f Specifically, we deposited an ultrathin platinum him on an indium-tin oxide substrate and then immersed the resulting assembly into a chloroform/methanol (2 1, v/v) solution of 7. As observed with the gold electrodes (Fig. 7.5), the corresponding cyclic voltammograms show waves for the reversible reduction of the bipyridinium dications with a significant increase in 2p with the immersion time. In fact, is 0.8,1.5, and 3.1 nmol/cm2 after immersion times of 1, 6, and 72 h, respectively. Furthermore, the correlation between ip and v is linear after 1 h and deviates from linearity after 6 and 72 h. Thus, the bisthiol 7 can indeed form multiple electroactive layers also on platinum substrates. 

Photochemical hydrogen production via oxidative quenching of [Rufbipy) ]2 by methylviologen (l,l -dimetkyl-4,4 -bipyridinium dication)... 

The simplest complexes of this group are those that involve a pyridinium guest included in a host containing electron-rich aromatics. An example of this mode of complexation is the complex 66, formed by complexation of a tweezer-like aromatic host 67 and a dendritically appended bipyridinium dication 68 <2005AGE477, 2006JA637>. 

Benesi-Hildebrandt plots were linear in a low concentration range however, the linear relationship did not exist between the transition energies and the difference in the half-redox potential of 2V. The solvation of 2,2 -bipyridinium dication is relatively small compared with that of the 4,4 -isomer possessing a symmetrical molecular structure. This decreases the electrostatic interaction to lead to a low transition energy. The CT bands for Bu-V2+ and Bzl-V2+ with [Fe(CN)6]4 ions almost linearly increase in an absorbance upon near-UV irradiation, and the absorbance decreases progressively in the dark and even more rapidly upon heating. 

The hydroxybenzyl radical formed is a good electron donor radical and can be oxidized by suitable oxidants. The effectiveness of such a redox process was evidenced by a series of flash photolysis experiments in which the biradical was trapped by paraquat (l,r-dimethyl-4,4 -bipyridinium) dications, PQ2+, according to the following reaction ... 

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