Porphyrin/pyrene

The assembly of molecular components for light harvesting and charge separation in artificial photosynthetic systems is of current interest. To mimic the multistep electron transfer in natural systems, Imahori et al. prepared a mixed SAM that combines an artificial antenna system (pyrene) with an artificial reaction centre (porphyrin), to examine the possibihty of photoin-duced energy transfer in two-dimensional assemblies (Fig. 29, 20) [27,147]. The ratio of porphyrin pyrene in the mixed SAM estimated from the absorption spectra on the gold surface is significantly lower than that of the solution from which the SAM was prepared. The strong tz-tz interaction of... 

Although the supramolecules of SWNTs wrapped with porphyrin-containing polymers mentioned above were prepared by mixing SWNTs and the polymer in solution, a very stable complex of porphyrin-pyrene copolymer 49/SWNT was also synthesized by copolymerization of porphyrin and pyrene in the presence of soluble SWNTs as shown in Scheme 4 [132]. 

Scheme 4 Preparation of porphyrin/pyrene polymer 49 in the presence of soluble SWNTs [132]...

Scheme 22 Oxidation of pyrene with Fe-porphyrin catalysts...

Maehashi et al. (2007) used pyrene adsorption to make carbon nanotubes labeled with DNA aptamers and incorporated them into a field effect transistor constructed to produce a label-free biosensor. The biosensor could measure the concentration of IgE in samples down to 250 pM, as the antibody molecules bound to the aptamers on the nanotubes. Felekis and Tagmatarchis (2005) used a positively charged pyrene compound to prepare water-soluble SWNTs and then electrostatically adsorb porphyrin rings to study electron transfer interactions. Pyrene derivatives also have been used successfully to add a chromophore to carbon nanotubes using covalent coupling to an oxidized SWNT (Alvaro et al., 2004). In this case, the pyrene ring structure was not used to adsorb directly to the nanotube surface, but a side-chain functional group was used to link it covalently to modified SWNTs. 

Pyrenes appear to be once again amongst the most useful linkers, and the attachment of metal-complexed porphyrins has already been discussed in the section on small aromatic molecules. Porphyrin rings bearing a metal center can also be directly adsorbed on the CNTs sidewalls, and they have been shown to exhibit an increased charge transfer from the metal to the tubes, presumably mediated by the aromatic moieties [100]. A similar behavior is exhibited by the phthalocyanine-based complexes [101]. Other aromatic molecules can be used for appendages, including triphenylphos-... 

Another approach is based on n-n stacking, which utilizes the moderately strong interactions between delocalized n-electrons of nanocarbons and those in aromatic organic compounds, such as derivatives of pyrene [54,55], porphyrins [56,57], phthalo-cyanines [58] or combinations thereof [59], as well as peptides [60], DNA [61], benzyl alcohol [62] or triphenylphosphine [63]. These molecules are often modified with long... 

Fig. 5.5 Scheme of n-n stacking on nanocarbons (CNT shown in example) showing (a) pyrene, (b) porphyrin, (c) phthalocyanine, (d) benzyl and (e) triphenylphosphinederivatives. M, Rand Y groups vary and can be used for further hybridization. 

The overall oxygen sensitivity exhibited by an optical sensor is basically predefined by the Stern-Volmer constant Ksv. The sensitivity of the final optical oxygen sensor increases with Ksv [65]. Generally, high Ksv values are provided by the Pd- and Pt-porphyrin complexes, by Ru(dpp)3, and by pyrene. Fluorescence quenching by oxygen not only affects the fluorescence intensity of the dye, but also has an influence on its lifetime r (Fig. 6) ... 

Abstract Pressure-sensitive paint (PSP) is applied to the areodynamics measurement. PSP is optical sensor based on the luminescence of dye probe molecules quenching by oxygen gas. Many PSPs are composed of probe dye molecules, such as polycyclic aromatic hydrocarbons (pyrene, pyrene derivative etc.), transition metal complexes (ruthenium(II), osumium(II), iridium(III) etc.), and metalloporphyrins (platinum (II), palladium(II), etc.) immobilized in oxygen permeable polymer (silicone, polystyrene, fluorinated polymer, cellulose derivative, etc.) film. Dye probe molecules adsorbed layer based PSPs such as pyrene derivative and porphyrins directly adsorbed onto anodic oxidised aluminium plat substrate also developed. In this section the properties of various oxygen permeable polymer for matrix and various dye probes for PSP are described. 

Figure 5.33 Structures of disulfide-terminated (a) pyrene (Pyr) and (b) porphyrin (Por), and thiol-terminated (c) boron-dipyrin (BoDy), (d) porphyrin (ThPor), and (e) the ferrocene-porphyrin-fullerene triad (Fc-P-C60)...

Imahori et al. reported on the energy transfer in mixed self-assembled monolayers of pyrene and porphyrin [83]. The molecular structures of the disulfide-terminated chromophores are illustrated in Figure 5.53. Porphyrin and pyrene dimers were coadsorbed onto Au(lll) mica substrates in different ratios. The ratios of pyrene to porphyrin were experimentally determined from absorption spectroscopy and the pyrene dimer was observed to adsorb preferentially, possibly due to its strong... 

Figure 5.53 Molecular structures of the (a) pyrene and (b) porphyrin monolayer components in the mixed self-assembled monolayers reported by Imahori et al. [83]...

Photophysical and photochemical studies recently reported describe the properties of rhodamine 6G in alcoholic and aqueous environment SDS micelles , psoralins dispersed in micelles , fluorescence enhancement of tetrakis (sulphonatophenyl) porphyrin in homogeneous and micellar solutionis quenching of pyrene by dibutylaniline in interaction with double chained surfactantsiS2, and a... 

Measurement of the influence of different micellar environments on proton transfer from excited states of 3-hydroxyflavone allows estimates to be made of micelle concentrations from measurement of the tautomer emission yield. Proton transfer reactions of benzimidazole excited singlet states have also been studied in ionic micelles. Magnetic fields are found to affect the behaviour of radicals generated by the photodissociation of benzil in micellar media. The starburst dendrites which are formed by anionic macromolecules in interaction with both anionic and cationic surfactants have been examined by pyrene fluorescence. Benzo[k]fluoranthrene fluorescence has served as a probe of the effects of metal salts on bile salt aggregation. The incorporation and distribution of benzoquinone into liposomes containing amphilic Zn(II) porphyrin has been followed by its effect on the quenching of the excited state °. A comparison of the photochromism of spirobenzpyran derivatives in unilamellar surfactant vesicles and solvent cast surfactant films has also been reported. ... 

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