Octaethylporphyrin spectroscopy

A range of neutral, singly and doubly oxidized heteroleptic double-decker complexes of the type [M(IV)(P)(Pc)](n), where n = 0, +1, or +2, M=Zr or Hf, P = the dianion of octaethylporphyrin (OEP) or tetraphenylporphyrin (TPP), and Pc = the dianion of phthalocyanine, has been reported. Each oxidized or reduced compound was characterized by UV-visible and/or EPR spectroscopy. The neutral compounds all undergo two reversible ring-centered oxidations and two reversible ring-centered reductions. The redox potentials were found to depend upon the type of macrocycle. They also vary with the size of metal ion in the case of oxidation but not in reduction, where E° values are relatively unaffected and shift by only 20-40 mV upon going from Hf(P)(Pc) to Th(P)(Pc), as compared to a much larger 220-280 mV shift between E° for the first oxidation of the same compounds [27]. 

Platinum porphyrin complexes can be prepared by reaction with PtCl2(PhCN)2. Purification of the final complex is by medium pressure liquid chromatography on alumina. The strongly phosphorescent platinum(II) porphyrin complexes are efficient sensitizers for stilbene isomerization. The quantum yields for the cis to trans process are greater than unity because of a quantum chain process in which the metalloporphyrin serves both as an energy donor and an acceptor.1110 Picosecond laser spectroscopy has been used to obtain time-resolved excited-state spectra of platinum octaethylporphyrin complexes, and to probe the excited-state energy levels.1111 Tetrabenzoporphyrin complexes have been prepared for platinum in both the divalent and tetravalent oxidation states. The divalent complex shows strong phosphorescence at 745 nm.1112... 

Studies on silver(II) porphyrins have largely been centred on synthetic porphyrins, such as H2TPP and octaethylporphyrin, H2OEP. However, a range of complexes based on heme derivatives have also been described.552 Some of these latter complexes have been characterized by IR spectroscopy.553... 

Triplet exclplexes formed from the triplet excited states of zinc and magnesium etioporphyrin I (ZnEtio I and MgEtlo I) and zinc octaethylporphyrin (ZnOEP) with acceptors such as nitro-aromatics and organochloro compounds were directly observed by conventional flash spectroscopy (250-252). The nature and decay properties of the exclplexes are sensitive to quencher concentration and medium composition. For example, as the concentration of para-nitrotoluene (PNT) was Increased in benzene solutions of ZnEtioI, the lifetime of the transient observed after flash excitation of the metal complex proportionately Increased up to a maximum and then decreased (250). The first effect was attributed to the formation of long-lived exclplexes involving two PNT molecules as shown in the scheme below, where D = metallopor-phyrin and A = PNT ... 

APD = avalanche photodiode detector APS = advanced photon source DFT = density functional theory ESRF = European synchrotron radiation facility HOPE = high-density polyethylene IR = infrared INS = inelastic neutron scattering KED = kinetic energy distribution Mb = myoglobin NIS = nuclear inelastic scattering NRVS = nuclear resonance vibrational spectroscopy NRIXS = nuclear resonant inelastic X-ray scattering OEP = octaethylporphyrin sGC = soluble guanylate cyclase VDOS = vibrational density of states. 

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