S-D dyad

Okayama, Japan. The synthetic procedures for S-D dyads and their reference compounds shown in Fig. 6 are illustrated in Fig. 7, where a naphthalene and a ferrocene moiety are used as an S and a D moiety, respectively. For comparison of photoinduced electron transfer rates between a single alkyl chain and a triple alkyl chain as the spacers of the S-D dyads with the same length of four-carbons, S-D dyads with a rigid spacer with a bicyclo[2.2.2]octane were synthesized [39]. The synthetic procedure for the S-D dyads with the rigid spacer is also shown in Fig. 8 [39], Other amphiphilic compounds and chemicals were commercially available. 

Figure 7. Synthetic routes for S-D dyads with a single alkyl chain. 

As described above, the arrangement of the various functional moieties was controlled spatially across the films at molecular dimensions in the form of LB films. In a series of folded type of sensitizer (S) and electron-donor (D) dyads in a previous work, however, the dyad molecules in the LB films can take many conformations due to flexibility of the longer alkyl chain of the dyads so that clear dependence of the photoinduced electron transfer rate on the alkyl chain length, i.e. S-D distance, was not observed [2], By this reason, we are studying the chain length dependence by using a series of linear type S-D dyads, in which the S and D moieties were linked by a single alkyl chain. In the closely packed LB films, the alkyl chain was considered to be extended and the distance between S and D to be... 

The absorption spectra of the mixed S-D dyads (1 1) and the reference compound (2-S) in cyclohexane are shown in Fig. 21 together with the absorption... 

Figure 21. Absorption spectra of (a) S-D dyads (3a 3b = 1 1), (b) 1-methyl-4-(2-naphthyl)bicyclo[2.2.2]octane (2-S), and (c) butylferrocene (Bu-Fc) in cyclohexane.

The transfer of the stable monolayers onto substrate plates and the comparison of the photoinduced electron transfer rates between S-D dyads with a rigid and a single alkyl chain spacer is now under investigation. 

Amphiphilic compounds and other chemicals used are shown in Figs. 5 [3,4] and 6 [36] together with their abbreviations. The synthetic procedures for A-S-D triad, A-S dyad, and H light harvesting antenna molecules in Fig. 5 were described previously [3,37,38]. A cationic cyanine dye with two long alkyl chains (CD) in Fig. 5 was purchased from Japanese Research Institute for Photosensitizing Dyes,... 

In Fig. 15 are shown UV-visible absorption spectra of type a and type b of 15 bilayers consisting of an alternate A-S-D triad-CaT (1 5) and a pure CaT mono-layer and type a of 15 bilayers containing A-S dyads in place of the triads. Hie LB films of type a were deposited on quartz plates, but the LB film of type b on a chemically modified quartz plate by octadecyltrichlorosilane. An absorption peak around 450 nm can be assigned to the acylated perylene moieties for the dyad and... 

Kuciauskas D, Lin S, Seely G R, Moore A L, Moore T A, Gust D, Drovetskaya T, Reed C A and Boyd P D W 1996 Energy and photoinduced electron transfer in porphyrin-fullerene dyads J. Phys. Chem. 100 15 926-32... 

Two simple supramolecular dyad systems, containing a chromophoric component called sensitizer (S) and a covalently linked acceptor (A) or donor (D) component,... 

Structural formulas of the ZP and ZP-I dyads are shown in Fig. 1. The absorption spectra of ZP-I dyads indicate that the excitation energies of the ZP S2 and S, states are practically the same throughout the ZP-I series. The peak position of the Soret absorption band of the ZP-I dyads are only slightly red shifted from that of free ZP, and are practically the same as that of ZnAr3P. These results indicate a rather weak D-A electronic interaction in the ground state of ZP-I systems despite of their directly linked structure, which can be ascribed to the nearly perpendicular conformation between ZP and I molecular planes [2],... 

Polymerization of propylene oxide-a-d was carried out by the EtZnNBu ZnEt catalyst in benzene solution in the presence of varying amounts of added water at 70° C, and was terminated after 7 days. The microstructure of the crude polymer was determined by the 1H-NMR method and the yields of amorphous and crystalline polymers were determined by a fractionation method (Fig. 16). When the amount of added water was increased up to 0.3 mole per mole of catalyst, the yield of crystalline polymer increased remarkably, whereas that of amorphous one remained nearly constant, and the isotactic dyad content (I) increased remarkably while syndiotactic one (S) remained almost constant. Thus, the striking parallel was observed between the yield of crystalline polymer and the isotactic dyad content, and between the yield of amorphous polymer and the syndiotactic dyad content. It is therefore concluded that water contributes more remarkably to the formation... 

Hviid and co-workers have recently found a way around this limitation by using the method of intermolecular triplet sensitisation to generate the locally excited triplet state of the donor chromophore in a D-A dyad.222 The sensitiser scheme is described by equations (35)-(38) and is also illustrated graphically in Fig. 36 for the case of triplet sensitisation of a donor chromophore (S is the sensitiser molecule). The principal advantage of this method is that the locally excited triplet state of one of the chromophores (in this case, the donor) is populated without invoking its... 

Khersonsky, O., Tawfik, D.S. (2006). The histidine 115-histidine 134 dyad mediates the lactonase activity of mammalian serum paraoxonases. J. Biol. Chem. 281 7649-56. 

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