Excited porphyrine

Table II presents the vadues of v, the rate constant for the electron transfer reaction with the donor and acceptor in contact, calculated by deconvolution of the fluorescence decay curves for a number of excited porphyrin-cOkyl halide systems. It appears that the rate parauneter depends strongly on the calculated exothermicity for these reactions. Parauneter i/ contadns information about the Framck-Condon factor of the electron-tramsfer reaction, which is in itself dependent on the reaction exothermicity and reorgauiization energy (22.23). Whether the rate constauit for the electron-transfer reactions depends on the exothermicity in the manner predicted by theory, that is with a simple Gaussian dependence (22), cannot be ainswered at present because of the uncertainties in the energetics of the particular reactions studied here.

Investigations of the photoinduced electron transfer between fullerenes and porphyrines show that electron transfer occur from the porphyrin to 3C o/3C o-Additionally, due to the absorption of the porphyrines at the excitation wavelength, electron transfer from triplet-excited porphyrine to fullerene may occur. Both pathways lead to the radical ion pair, the ratio depends on the ratio of con-... 

The fluorescence lifetime measurements of 25 and 26 in solution suggest that the quenching of the singlet excited porphyrin by the attached Ceo is a major deactiva-... 

Addition of an inorganic sheet and a PVT-MV + layer results in efficient quenching of the porphyrin phosphorescence at 720 nm, due to electron transfer from excited porphyrin to MV +. Electron-transfer quantum yields were calculated as 0.58 and 0.76 for a-ZrP and HTiNbOs spacers, respectively. Figure 38 shows the steady-state emission spectrum of such a multilayer system. 

Another example of self-assembly of porphyrin-containing polymer was illustrated by Li et al.73 Polyacetylene functionalized with fullerene and zinc porphyrin pendant groups were synthesized by polymerizing the corresponding fullerene/porphyrin substituted alkyne monomers with rhodium(I) norbomadiene catalyst (Scheme 5.5).74 Polymers with different ratio of C60 and porphyrin were synthesized. The polymers showed photocurrent response when the thin films were irradiated with white light, which was due to the electron transfer from the photo-excited porphyrin to the C60 units. In addition, the copolymers aggregated into ellipse-shaped nanorod structures with a diameter of approximately 100 nm and a length of... 

Whitten and co-workers [230] have amply investigated stilbene isomerization induced by excited porphyrins. Electron-deficient nitrostilbenes quench excited Zn or Mg etioporphyrins through exciplex formation. Light absorbed by the porphyrin affects isomerization of 4-nitro- or 4,4 -dinitro-stilbene with low quantum yields ((%trans)sens = 99.5), possibly via a stilbene exchange chain mechanism [230]. Azastilbenes coordinate to me-talloporphyrins in both the ground and the excited state (but do not quench it), and isomerize efficiently upon selective excitation of the porphyrin [231]. Complexed 1,4 -NPE gives d , = 6.6, = 0.2, and (%trans)sens = 96,... 

What is the role of energy or electron transfer in the quenching of tetrapyrrole fluorescence by carotenoids In other model studies the redox levels of a porphyrin-carotenoid dyad have been shown to influence the quenching mechanism to the extent that electron transfer from the carotenoid to the excited porphyrin was shown to occur (Hermant et al., 1993). However, in a series of carotenoid-porphyrin dyads in which the number of conjugated carbon-carbon double bonds in the carotenoid moiety was systematically increased from 7 to 11, quenching... 

This biological membrane system is ideal for porphyrin-based energy conversion systems. For energy storage by photoinduced vectorial charge separation, the elecfron must be removed faster from the excited porphyrin than about IG ps in order to avoid deactivation. Thereafter, the electron should be kept at a... 

Dyads of free base and Zn-complexed porphyrins and Cgo (8) were prepared by Gust and coworkers [109], When the porphyrin moiety in the dyads is photoexcited, there is intramolecular energy transfer from the excited porphyrin to the fullerene moiety, generating the excited singlet state of C. For the dyad consisting of Zn-complexed porphyrin, the Cjq excited singlet accepts an electron from the porphyrin, resulting in the formation of C q radical anion and porphyrin radical cation [109]. 

Rodriguez, J. Kirmaier, C. Holten, D., Time-resolved and static optical properties of vibrationally excited porphyrins. J. Chem. Phys. 1991, 94, 6020-6029. 

Hasobe T, Fukuzumi S, Kamat PV (2006) Organized assemblies of single wall carbon nanotubes and porphyrin for photochemical solar cells charge injection from excited porphyrin into single-walled carbon nanoubes. J Phys Chem B 110 25477-25484... 

---