Resonance condition porphyrin

Of special Interest as O2 reduction electrocatalysts are the transition metal macrocycles In the form of layers adsorptlvely attached, chemically bonded or simply physically deposited on an electrode substrate Some of these complexes catalyze the 4-electron reduction of O2 to H2O or 0H while others catalyze principally the 2-electron reduction to the peroxide and/or the peroxide elimination reactions. Various situ spectroscopic techniques have been used to examine the state of these transition metal macrocycle layers on carbon, graphite and metal substrates under various electrochemical conditions. These techniques have Included (a) visible reflectance spectroscopy (b) laser Raman spectroscopy, utilizing surface enhanced Raman scattering and resonant Raman and (c) Mossbauer spectroscopy. This paper will focus on principally the cobalt and Iron phthalocyanlnes and porphyrins. 

TPP)MnOAc (18) is an excellent initiator of the polymerization of the ringopening polymerization of PO. An example is illustrated in Fig. 52, where 400 equiv of PO was consumed completely in about 20 h at 30 °C. The NMR spectrum of the polymer shows a simple resonance pattern due to the CH3 group (6 17.4 ppm), indicating that the polymer consists exclusively of head-to-tail linkages. The NMR spectrum was also informative concerning the stereoregularity of the polyether, where the obtained polyether was almost atactic (i/s= 0.54 0.46,1/H/S=0.28/0.50/0.22). This is in contrast to the case with the aluminum porphyrin as initiator, which produces a polymer rich in isotactic triad sequences under similar conditions. 

A more quantitative estimate of the pseudocontact shifts in DeutCN was obtained from comparison of the methylester resonances in DeutCN and deuteroporphyrin IX zinc(II) (114). Under identical conditions these resonances were both at —3.72 ppm from DSS in the diamagnetic complex, and at —3.78 and —3.82 ppm in DeutCN. The observed shift of ca. —0.08 ppm has to come almost entirely from pseudocontact coupling, since delocalization of unpaired spin density to these positions must be negligibly small, and a small change of the porphyrin ring current field, which might result from the zinc(II) vs. iron(III) substitution, would hardly be noticeable at the methylester positions either. With the assumption of an axially symmetrical g-tensor, and rj -values for the different protons of 10.0, 6.4, 5.7, and 4.5 A (Hoard (41)), one then estimates from the fj 3-dependence (Eq. 10) that the corresponding... 

To date very little is known about the coordination chemistry of the sapphyrin macrocycle, and no complexes have been reported for the dioxosapphyrin or the thiosapphyrin. In the free-base form, sapphyrin is a potential trianionic ligand and thus, on paper at least, seems perfectly suited for complexing the normally trivalent cations of the lanthanide series. Presumably, lanthanide(III) complexes of sapphyrin, which would be neutral (and potentially useful for magnetic resonance imaging applications see Sect. 12.2), would be expected to form easily under typical porphyrin metalation conditions. However, in spite of the apparent correspondence in the sapphyrin core size and the ionic radii of the lanthanides, to date no lanthanide cation has been inserted into the core of the sapphyrin macrocycle using a variety of standard metal insertion techniques [156]. Nor, have any other pentaligated complexes of any other metal cations been reported to... 

In order to elucidate the role of the resonance energy transfer (RET) in NC LQ quenching, titration curves have been recorded for CdSe/ZnS NCs of a given diameter (dCdse=2.5 nm and dCdse=2.6 nm, 2 ZnS monolayers) and porphyrins having various absorption spectra (Fig. 1) but same passivation conditions. 

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