Porphyrinic groups linked

Fullerenes such as C60 are excellent electron acceptors. In a fullerene-porphyrin-based dyad, the photoexcited state of the Qo accepts an electron from the linked zinc porphyrin group to give a charge-separated state. 

As a complement, Shiga et al. reported on porphyrins that link to the Ti02 nanoparticles by using a fullerene bearing carboxylic acid groups (Fig. 18.7) [116]. Although the authors measured very low efficiencies of around 0.53 %, the success of their approach was demonstrated by the incident photo-to-current efficiency spectra, in which the porphyrin features, that is, the Soret band, are discernible. In addition, they reported extraordinary stabilities with values up to 3000 hours. 

Photochromism has also been observed when two porphyrinic groups are linked to a dithienylethene scaffold. The closed form showed an absorption band at 560 nm (01JA1784). The same behavior was observed in the system 318-319 (02AM918). Dithienylethene photochromic systems have also been described to be linked to single-walled nanotubes (07JA12590). 

The conductivity of a generic semiconductor film is likely to be modulated by absorption of a polar species on the film surface. For example, a group at the Weiz-mann Institute has examined GaAs surfaces and found that porphyrin receptors linked to it will attract nitrogen oxide NO, and the binding of NO caused a change in resistance [5]. Other embodiments of GaAs sensors were found to be sensitive to ions in solution [25]. 

Five years later, Gust s group [34] developed another triad incorporating a porphyrin (P) linked to a dithienylethene (DTE) and a fulgimide (FG) (Scheme 6). The main synthetic approach was still the Sonogashira coupling of dithienylethene and fulgimide-appended zinc porphyrin (FG-PZn-DTE). Trifluoroacetic acid-induced demetalation of FG-PZn-DTE produced FG-P-DTE in 57% yield. 

Figure 7. Supramolecular cage-like compound 6 formed through 12 H bonds between two porphyrins covalently linked to 5-alkyluracil recognition groups, and two alkyltriaminopyrimidine units.

Porphyrin ligands are dianionic ligands containing four nitrogen donors. The core of the porphyrin ring, shown in Figure 4.7, consists of four pyrrole groups linked by methene... 

A light-harvesting array was attempted in a five-porphyrins system linked by a diphenylethyne group [638,639] (23). The center-to-center distance was around 20 A. Excitation of the surrounding four Zn porphyrins induced singlet energy transfer with 90% efficiency to emit fluorescence m the central free-base poiphyrin. 

Chlorophylls and pheophytins. Chlorophyll pigments are widely spread in the natural environment, chlorophylls a and b being the most abundant. Chlorophylls are included in the porphyrin group. They have a basic common stmcture, the porphin, with four units of pyrrole linked at the alpha positions by methylene bridges in a planar aromatic system, which is highly stable and amenable to the formation of chelates with metal ions. For the chlorophylls, the metal ion that forms the complex is Mg (Shahidi, 1997). 

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