Octaethylporphyrin electron transfer

Transfer of an electron from a photoexcited donor to an acceptor has also been studied. Ballard and Mauzerall [219] photoexcited zinc octaethylporphyrin and found both the triplet—triplet rate coefficient and ion yields indicate a reaction radius of 2.0 0.1 nm, some 0.6 nm larger than twice the radius of this metal ligand. However, electron transfer from pyridine—ruthenium complexes does not appear to be facilitated by electron tunnelling (see Chap. 3, Sect. 2.1). 

According to the data from Smalley [234] the quenching of the fluorescence of magnesium octaethylporphyrin proceeds via electron tunneling in statistical pairs. The distances between the reactants and the characteristic time of electron transfer in the pairs are 10-18 A and 5 ns, respectively. 

Photoinduced intramolecular electron transfer in porphyrin triads of 4he type [zinc octaethylporphyrin-4,4 -bipyridinium-tetraphenylporphyrin] occurs either from the singlet state of the zinc porphyrin ( A) or from the corresponding free base ( B) with formation of or An... 

Self-assembly principles of the formation of multiporphyrin arrays are extended to anchor the porphyrin triads on semiconductor CdSe/ZnS quantum dot (QD) surface. Comparing with individual counterparts (QD, pyridylsubstituted porphyrin H2P(p-Pyr)4, and Zn-octaethylporphyrin chemical dimer (ZnOEP Ph), the formation of heterocomposites QD-porphyrin triad results in the specific quenching of QD photoluminescence, accompanied by the dimer fluorescence strong quenching (Tsd 1-7 ps due to energy and/or electron transfer) and the noticeable decease of the extra-ligand H2P(p-Pyr)4 fluorescence efficiency by 1.5-2 times via hole transfer H2P—>dimer. 

The electron self-exchange rate constants for several Fe(II)/Fe(III) porphyrin couples have been measured by H NMR line-broadening techniques in 5 1 acetone/water at -20 The relative rate constants for the [Fe(P)(l-MeIm)2] couples, P = octaethylporphyrin chlorin < isobacteriochlorin, have been attributed to differences in outer-sphere reorganization, related to the steric bulk. The rate-determining step in the metallopophyrin-catalyzed reductions of dioxygen by substituted ferrocenes is the electron transfer between the ferrocene and the metalloporphyrin (M = Fe, Co, and The Marcus relationship provides a... 

Aoyama et al. [76] have described a more direct approach in which 5,15-cis-bis(2-hydroxy-l-naphthyl)octaethylporphyrin is used to bind p-quinones in chloroform solution (13). This strategy positions the quinone in a face-to-face orientation immediately on top of the porphyrin plane. The quinone quenches porphyrin fluorescence, presumably due to photoinduced electron transfer, but time-resolved fluorescence or transient absorption studies have not been reported, to date. The close proximity of the reactants, however, is expected to favor rapid electron transfer. 

It is noteworthy that siroheme is present in the enzymes responsible for catalyzing two out of only three known six-electron processes, and accordingly it is of great interest to try and identify any feature in siroheme that makes it particularly suitable for the mediation of multielectron transfer. A comparison of octaethylporphyrin, octaethylchlorin and octaethylisobacteriochlorin complexes of iron shows that redox potentials and vco of Fe(P)L(CO) and Fe(P)L(CO)2 were nearly independent of the porphyrin. The property that was most dependent upon the macrocycle structure was the potential for ring-based oxidation which increased in the order OEiBC < OEC < OEP.734... 

Hexylthiophene coimected to octaethylporphyrin through a diacetylene linkage has been synthesized and the effect of substituents (like H, Br, CN, CHO, NO2) on the electronic properties were studied <03TL5423>. It was reported that the absorption maxima were greatly influenced by the substitution as they increase the intramolecular charge transfer through the diacetylene linkage. This effect was reported to be more pronounced in the thienyl linked porphyrin in comparison to the phenyl linked ones. 

The kinetically best characterized system for which a bimolecular reductive elimination has been proposed is a neutral hydrido porphyrin derivative of Ru(III) [4]. Cyclic voltammetry and double potential step chronoamperometry afford data that are more consistent with a second order than with a first order decay for the 17-electron RuH(OEP)(L) (OEP = octaethylporphyrin L = THE, 1 -tert-bytyl-S-phenylimidazole) complexes in THF as solvent. The second order dependence of the rate constant and the independence on the parent 18-electron anion concentration exclude the proton transfer mechanism. The possibility of a disproportionation mechanism (which would afford the same second order dependence, see section 6.5.2), however, has not been considered, nor were studies in solvents other than THF carried out. In the light of the gathered information, the mechanism shown in Scheme 17 was proposed. 

Zr(IV), and Ce(IV) as the central metal ion. Copper(II) porphyrins are among the most studied of the paramagnetic metalloporphyrins. The Cu(II) complexes show a low-temperature luminescence that arises from the and states that exist in thermal equilibrium. These two states are derived from the lowest excited triplet state on the porphyrin ring, which is split because of the presence of a unpaired electron on the Cu(II) center. Transient absorption measurements show that the ambient temperature excited-state decay times are lowered when a ligand is associated with the axial coordination positions of the tetracoordinate Cu(Il) porphyrin complex. The excited state lifetimes of Cu(II) porphyrin complexes in solution can be either dependent or independent of the temperature and solvent. For the octaethylporphyrin complex Cu(OEP) the excited state lifetime increases as the temperature is lowered, and also as the solvent polarity is increased. By contrast, the excited state lifetime of the tetraphenylporphyrin Cu(TPP) is insensitive to both the temperature and the polarity of the solvent. This difference in their photophysical behavior is likely due to a difference in the energy gap between the charge transfer state and the T/ T states in the pair of complexes. 

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