Viologen, electronic spectrum

The two species approach in solution to form a sandwichlike 71-complex, and electron transfer takes place with formation of the dimer, whose dissociation leads to radical 2+. Electrochemical results as well as the EPR spectrum observed by reduction of the multicharged viologen Af-ethyl-AAtrimethylaminopentyl-4,4 -bipyridine (C5V3+, 19) indicated that dimerization proceeds through a radical-... 

Fig. 2. (A) K-band ESP-EPR spectra of the CPI complex (top) and Rb sphaeroides R26 reaction-center complex (bottom) in the charge-separated states [P700 -A,4 and [P870 Q4, respectively (B) X-band ESP-EPR spectra of spinach PS-I particles extracted with a hexane-MeOH mixture (a), reconstituted with protonated (b) and deuterated (c) vitamin Ki (C) ESP-EPR spectra of spinach PS-I particle in glycine buffer at pH 10.8 and untreated (a), reduced with 50 mM dithionite and 0,5 mM methyl viologen and dark-incubated (b), and the reduced sample dialyzed overnight against glycine buffer and reconcentrated (c). Figure source (A) Petersen, Stehlik, Gast and Thurnauer (1987) Comparison of the electron spin polarized spectrum found in plant photosystem I and in iron-depleted bacterial reaction centers with time-resolved K-band EPR evidence that the photosystem I acceptor is a quinone. Photosynthesis Res 14 22 (B) and (C) Snyder and Thurnauer (1993) Electron spin polarization in photosynthetic reaction centers. In J Deisenhofer and JR Norris (eds) The Photosynthetic Reaction Center, Vol 11 313,315.

The matrix molecules of the mixed dye and acceptor monolayers have been omitted for clarity. Absorption spectrum of the viologen radical formed by the photoinduced electron transfer under nitrogen atmosphere, measured with an assembly of 5 dye-acceptor units with molar ratios of dye arachidate = 1 20 and acceptor to arachidate = 1 10. 

Figure 5. Observed photosensitized absorption in dye aggregate-viologen monolayer system compared with literature spectrum of the radical produced from one-electron reduction of dimethylviologen (36).

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