Electron 1,1 -dicyano vinyl

Figure 2 shows the structures of the bifunctional model systems l(n), (n=4,6,8,10,12), investigatedThe synthesis of these systems and a discussion of their electrochemical properties as well as of their electronic absorption and emission spectra have been given elsewhere (Oevering et al., 1987). These molecules contain a 1, 4-dimethoxynaphthalene unit as the photoexcitable electron donor (E./2 =+1.1 V vs. see in acetonitrile) and a 1,1-dicyano-vinyl moiety as a moderately powerful electron acceptor (Ev=-. l V) separated by an array of at least n C-C sigma-bonds. The centre-to-centre separation (Rc) and the edge-to-... 

Now, the crucial question is, how is the electron transition So Si of such a push-pull system changed, when the chromophores in 52 are extended ( = 1, 2, 3,...) Figure 11.15 reveals the expected red-shift in the simply donor-substituted series 52a n = 1-5). This effect is preserved for 52b with CN groups as weak acceptors. In the formyl series 52c, the absorption maidma are almost independent of the size of the conjugated chromophore and the nitro series 52d shows a distinct hypsochromic effect. The latter effect is even more pronounced for the dicyano-vinyl series [210, 211, 213). How can this unexpected behavior be explained We found that the blue-shift in the DAOPV series is restricted to measurements in normal organic solvents like CHCI3. As soon as a protonation occurs, the hypsochromic effect is reversed to a bathochromic effect (Fig. 11.16). 

Meisel etal. [18-20] were the first to investigate how the addition of a polyelectrolyte affects photoinduced ET reactions. They found that charge separation was enhanced as a result of the retardation of the back ET when poly(vinyl sulfate) was added to an aqueous reaction system consisting of tris(2,2 -bipyridine)ruthenium(II) chloride (cationic photoactive chromophore) and neutral electron acceptors [21]. More recently, Sassoon and Rabani [22] observed that the addition of polybrene (a polycation) had a significant effect on separating the photoinduced ET products in an aqueous solution containing cir-dicyano-bis(2,2 -bipyridine)ruthenium(II) (photoactive donor) and potassium hexacyano-ferrate(III) (acceptor). These findings are ascribable to the electrostatic potential of the added polyelectrolytes. 

Electron-transfer Initiation. Highly electron-rich monomers like A-vinylcarbazole can be polymerized readily by powerful electron acceptors such as chloranil, tetracyanoethylene, and 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ). Recently the killing of polymerizations at low conversion by addition of methanol has shown that the ion radicals initially formed combine to give a zwitterion in the case of DDQ with methyl vinyl ether (Scheme 6), although to what extent this structure is maintained throughout polymerization is not certain. 

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