Organic solvents effect electron-donor solvent

Polymerization of butane-1,4-diol dimethacrylate, sensitized by benzophenone in the presence of three different sulfides, has been described by Andrzejewska et al. [190]. The measurements show that in the absence and in the presence of propyl sulfide and 2,2 -thiobisethanol no polymer was formed. This can be explained by the effective back electron transfer process that occurs in the radical-ion pair in organic solvents. Effective polymerization was observed only in the presence of TMT. Laser flash photolysis studies performed for the benzophenone-TMT pair allow one to construct a scheme (Scheme 23) explaining characteristic features of the mechanism of polymerization initiated by the system. The results prompted the authors to study other symmetrically substituted 1,3,5-trithianes as electron donors for benzophenone-sensitized free-radical polymerization (Figure 38 Table 12) [191]. 

Separation of D and A centers by non-conducting media resulted in the strong dependence of the ET rate on distance between D and A and the marked effect of the chemical nature of saturated molecules and bonds between the pair. This dependence can be quantitatively characterized be the decay factor, (3, (Eq. 2.27). The following values of P (in A 1) were found 3-4 (vacuum), 1.6 - 1.75 (water), 1.2 (organic solvents) and 1.08 -1.2 (synthetic D-bridge-A molecules). The effects of distance and the number of intermediate saturated groups (n) on photoinduced electron transfer between a donor and acceptor are discussed in (Verhoeven, 1999). 

In the initial description of the cationic dye-borate system [24, 76], it was postulated that electron transfer was possible because, in nonpolar solvents, dye/borate salts exist predominantly as ion pairs. Since the lifetime of the cyanine singlet excited state is quite short [24, 25], this prerequisite is crucial for eflfective photo-induced electron transfer. Recently initiator systems in which neutral dyes are paired with triarylalkylborate anions have appeared in the literature [77]. In the latter case, the borate ion acts as the electron donor while neutral merocyanine, coumarin, xanthene, and thioxanthene dyes act as the electron acceptors. It is obvious that these initiating systems are not organized for effective electron transfer processes. The formation of an encounter complex (EC) between excited dye and electron donor is required. 

The ethylene spacer is necessary as a shield from the strong electron-withdrawing effect of the perfluoroalkyl chain, which would decrease the donor properties of the phosphane. This phosphorous-ligand is extremely soluble in per-fluorinated solvents such as perfluoromethylcyclohexane (CFgCsFn) and only trace amounts of it can be extracted with organic solvents. The in situ prepared rhodium(l) complex 14 is a useful catalyst for the hydroformylation of terminal alkenes under FBS-conditions. The aldehydes 16 and 17 were formed in 85% yield by hydroformylation of 1-octene (15) with an linear to iso ratio of nearly 3 1 Eq. (8). 

The electron donor-acceptor molecular complexes between iodine and thiazole, benzothiazole, and some derivatives have been studied in several organic solvents by UV spectroscopy <87CJC468>. In all cases, the presence of the thiazole ring produces a displacement of the Amax iodine band at 512 nm towards shorter wavelengths and a decrease of its absorbance. Moreover, a sharp isosbestic point near 470 nm was observed for all iodine-thiazole complexes. 2-Aryl and 2-hetarylbenzothiazoles showed fluorescence, the maxima of emission being between 350 nm and 395 nm. Both substituent and solvent effects on the spectra were observed <93MI 306-02>. The photophysical properties of bis(benzothiazolylidene)squaraine dyes have also been studied <93JPC13625>. 

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