Porphyrins monomers

Secondly, Fig. 5 shows that the polymeric rate constants parallel values of heterogeneous rate constants that have been observed for the electrochemical reactions of solutions of the corresponding dissolved porphyrin monomers. (The slope of the line is 0.5). This re-emphasizes what was said above, that measurements of electron hopping in polymers can give rate constants that are meaningful in the context of the metalloporphyrin s intrinsic electron transfer chemistry. 

Campidelli et al. have synthesized interesting linear and hyperbranched porphyrin polymers from CNTs via copper-catalyzed alkyne-azide cycloaddition (CuAAC) [122], Zinc porphyrin monomers containing an azide group and one or three alkyne groups were synthesized and chemically bound to alkyne functionalized SWCNTs via CuAAC. Depending upon the number of alkyne functionalities either linear (single alkyne) or dendrimer-like (triple alkyne) porphyrin polymers were produced (Fig. 5.9) [122],... 

Table II. Zero-field Splitting parameters (in 10 cm ) and average triplet lifetimes of porphyrin monomers and dimers ...

The use of porphyrins as sensitizers for the nano-crystalline electrode in DSSC is particularly attractive given their important role in photosynthesis and the relative ease modification on molecular structure. Not only the porphyrin monomers, but also the large porphyirn arrays have been tested extensively as sensitizers of wide-band-gap semiconductors like NiO, ZnO and Ti02 in the past several decades. The focus of this section is the various molecular structure modification of porphyrins for the purpose of applying as sensitizer in DSSCs. 

Another interesting work conducted by Wamser and co-workers in the field of porphyrin monomer sensitizers is the functionalization of tetraphenylporphyrin at the para positions of -phenyl with one amino group and three carboxylic acid groups. The resulted asymmetrical porphyrin (45) can be successfully fabricated into a modified solid Gratzel type cell with polyaniline as the solid electrolyte. The overall energy conversion efficiency of this cell is about 2% with a number of opportunities to optimize the efficiency remaining [81]. 

In a later research, Sereno and co-workers found efficient energy transfer from zinc porphyrin to metal-free porphyrin in the dyad (90) even in the adsorbed states. The fact that the dimer is less effective in comparison with metal free porphyrin monomer in the generation of photocurrent is explained as that the metallized porphyrin enhances the back electron-transfer process [96],... 

Controversial results have been deduced from the researches of different groups on the sensitization behavior of porphyrin arrays as mentioned above. Some of them revealed that porphyrin arrays have advantages over porphyrin monomers in the sensitization of wide band gap semiconductor while the rest showed the opposite results. The porphyrin dimer composed of a metal free porphyrin and a zinc porphyrin seems the most successful porphyrin array sensitizer so far. Programing the photoinduced energy and electron-transfer sequence in a porphyrin array is the key step toward a good porphyrin array sensitizer. 

Under short-circuit conditions the cathodic photocurrent was observed for the photoelectrochemical cell the quantum yield was ca 0.5 % [309, 318, 332]. The photocurrent intensity in the free-base porphyrin-Ceo system was enhanced fivefold compared with that in the corresponding free-base porphyrin monomer system. Such enhancement of the photocurrent demonstrates that C6o acts an effective mediator in a sequential electron-transfer process. The photocurrent intensity in the free-base porphyrin-Ceo cell was ca one order of magnitude larger than that in the zinc porphyrin-Cfio cell [309, 318, 332]. Two different electron-transport mecha-... 

The three side-on views of the molecular structures for 5-7, shown in Fig. 4, confirm the ability of the xanthene bridge to hold two porphyrin rings in a cofacial arrangement, akin to what is observed for the analogous anthracene and biphe-nylene systems. Pertinent geometrical parameters are summarized in Table I. Scheldt and Lee s semiquantitative scheme for the pairwise overlap of the n systems of spatially oriented porphyrin monomers within the crystalline lattice... 

More recently, a diastereoselective molecularly imprinted fluorescent polymer for (-)-cinchonidine was prepared by the combined use of methacrylic acid and vinyl-substituted zinc(II) porphyrin monomer as functional monomers [24], Compared to the reference imprinted polymers using either MAA or zinc(II) porphyrin as a functional monomer, the imprinted polymer prepared with both MAA and the porphyrin... 

Porphyrin monomers and organized monolayers on conducting or semiconducting surfaces provide the unique possibility to convert the energy of the excited state directly into photocurrents. Furthermore, the large porphyrin surface allows... 

Tetracationic me o-tetramethylpyridinium porphyrin and the anionic lipid L—dimyristoylphosphatidic acid mixed in a ratio of 1 4 form a monolayer on glass. It shows the spectrum of porphyrin monomers, again lying flat on the surface, whereas on water surfaces they appear as stacked dimers. Only those molecules that had been directly attached to the anionic lipid layer on water were transferred to the glass plate (Fig. 6.8.1). The tendency of porphyrin monomers... 

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