Electron spin polarization in the photoexcited triplet state of porphyrins

Levanon, Haim; Wolberg, Alexander

doi:10.1016/0009-2614(74)80223-x

Cited by 21 publications

(6 citation statements)

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“…The graphical representations of molecular orbitals and iso spindensity surfaces were achieved using the Molden program package. 49 13,19,21 The absolute signs of D and E are not directly determinable from the spectra, so the modulus is given. The values for D and E from this work together with the literature values are collected in Table 1.…”

Section: 1mentioning

confidence: 99%

“…Hence, in the present contribution, we have performed time-resolved ENDOR on both 3 H 2 TPP and 3 H 2 P. Thus, we have been able to resolve the hfcs of the α protons (3) in 3 H 2 P and can compare the proton hfcs of both molecules. This is interesting as it has been known for many years that the zfs parameters of H 2 TPP are much smaller than those of H 2 P. , It was considered possible that the LUMO and LUMO+1 might be reversed between the two molecules or that some electron density might be delocalized onto the phenyl rings. A more quantitative interpretation has until the present time not be attempted as the calculation of zfs parameters using either semiempirical or ab initio methods yields only mediocre agreement with experimentally determined values. ,− …”

Section: Introductionmentioning

confidence: 99%

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The Electronic Structure of the Photoexcited Triplet State of Free-Base (Tetraphenyl)porphyrin by Time-Resolved Electron−Nuclear Double Resonance and Density Functional Theory

Kay

2003

J. Am. Chem. Soc.

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The photoexcited triplet states of free-base porphyrin (H(2)P) and free-base tetraphenylporphyrin (H(2)TPP) have been investigated by time-resolved electron paramagnetic resonance and electron-nuclear double resonance in a toluene glass at 80 K. Both the zero-field splitting parameters, D and E, and the proton A(zz) hyperfine coupling tensor components could be determined. D is about 13% larger in H(2)P than in H(2)TPP. In contrast, however, the A(zz) hyperfine coupling tensor components showed differences of less than 2%. To aid the understanding of these results, the electronic structures of H(2)P and H(2)TPP have been modeled using density functional theory. The geometrical structures of both molecules in their lowest triplet states were calculated using the Becke3 Lee-Yang-Parr composite exchange correlation functional and the 6-31G* basis set. Hyperfine couplings for these structures were calculated using the same functional but with the extended EPR-II basis set. These allow unambiguous assignment of the experimentally determined couplings. The theoretical values for H(2)P and H(2)TPP agree with the experimental values in that the presence of the phenyl groups has only a small effect on the unpaired electron spin-density distribution. The difference in sensitivity of the zero-field splitting parameters and the hyperfine couplings to mesophenyl substitution is discussed in terms of the wave functions of the four frontier orbitals of porphyrins introduced by Gouterman.

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Section: 1mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The Electronic Structure of the Photoexcited Triplet State of Free-Base (Tetraphenyl)porphyrin by Time-Resolved Electron−Nuclear Double Resonance and Density Functional Theory

Kay

2003

J. Am. Chem. Soc.

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“…That environmental constraints may considerably change the energies of the porphyrin excited states has been demonstrated for zinc tetraphenyl porphyrin in a hydrophobically modified polysulfonate matrix (Morishima et al, 1995). In Zn4Hb and Mg4Hb the conformation of the porphyrin molecule in its triplet state is reflected by the symmetry properties of the zero field splitting (ZFS) tensor, as follows from the Am = ±+ I triplet EPR spectra (Gouter- (in units (10-4 cm-1) and fwhm linewidth (ml) of the EPR (Z)-transitions man, 1973; Levanon and Wolberg, 1974). At low temperature (typically <100 K) the orbitally doubly degenerate lowest triplet state of metalloporphyrins exhibits a Jahn-Teller instability, which results in a symmetry-breaking distortion of the fourfold symmetric D4h molecule into two dynamically interconverting, equivalent vibronic states, both with D2h symmetry (Gouterman, 1973;Van Dorp et al, 1974;Hoffman, 1975Hoffman, , 1978Bersuker and Stavrov, 1981; Angiolillo and Vanderkooi, 1995).…”

Section: Discussionmentioning

confidence: 99%

Triplet state magnetic resonance and fluorescence spectroscopy of metal-substituted hemoglobins

Polm¹,

Schaafsma²

1997

Biophysical Journal

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Fluorescence detected magnetic resonance (FDMR) spectra detected at 596 nm of zinc-substituted hemoglobins at 4.2 K show a split D-E transition, which is not observed for zinc protoporphyrins ligated by methylimidazole in glasses. Incorporation of the zinc heme into the globin pocket is also accompanied by a blue shift of the fluorescence of 20 nm at 4.2 K. FDMR spectra recorded at 576 nm do not show the D-E splitting. The D-E splitting and the huge blue shift are not observed for the magnesium-substituted hemoglobins. Fluorescence measurements at 4.2 K and 77 K, and EPR measurements at 110 K, were carried out to obtain information about the ligation states of the zinc and magnesium protoporphyrins in glasses and in hemoglobin. The results are explained by considering ligation effects and distortion of the porphyrin plane.

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“…Extensive work has been done on the magnetic and optical parameters of the photoexcited triplet state of porphyrin molecules and related biological compounds [1,2,3,4]. Much less has been published on the kinetics of population and depopulation of the photoexcited triplet manifold, in particular at relatively high temperatures [5,6,7]. Moreover, free base porphyrins are of particular interest, since their photoexcited triplet state is apparently non-radiative.…”

Section: Introductionmentioning

confidence: 99%

“…The samples were irradiated by an electronically modulated Xenon arc (Eimac ISOwatt). The averaging technique of the photoexcited EPR signal, in the single pulse experiment, and its phase detection with reference to the light modulation frequency, in the CWexperiment, were described in detail previously [6,11].…”

Section: Introductionmentioning

confidence: 99%

Kinetic Study of the Photoexcited Triplet State of Free Base Porphyrins by EPR

Scherz

Orbach

Levanon

1974

Israel Journal of Chemistry

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An electron paramagnetic resonance (EPR) study of the photoexcited triplet state of four free base porphyrins is presented. The zero field splitting parameters (ZFS) |D| and |E| were calculated from the EPR spectra of the porphyrins dissolved in n‐octane matrices at 80°K. |D| = 0.0359 cm−1, |E| = 0.0079 cm−1 for tetra phenyl porphyrin (H2 TPP), |D| = 0.0432 cm−1, |E| = 0.0037 cm−1 for tetra (per‐fluoro) phenyl porphyrin H2T (per‐F) PP, |D| = 0.0366 cm−1, |E| = 0.0078 cm−1 for tetra (para‐chloro) phenyl porphyrin H2T(P‐Cl)PP, |D| = 0.0369 cm−1, |E| = 0.0076 cm−1 for tetra (para‐methyl) phenyl porphyrin H2T(P‐Me)PP. The transient behavior of the EPR signal intensities in the last two porphyrins is discussed. The depopulation rate constants of the triplet sublevels kp, the ratio between the population rate constants Ap (at zero field, p = x,y,z), and the spin lattice relaxation rate W within the triplet manifold, were calculated. kx = (12 ± 2) × 102 sec−1, ky = (0.5 ± 0.1) × 102 sec−1, kz = (1.2 ± 0.4) × 102 sec−1, Ax:Ay:Az ≃ 0.63:0.01:0.33, W = (0.4 ± 0.1) × 104 sec−1 for H2T(P‐Cl)PP, kx = (7 ± 2) × 102 sec−1, ky = (4 ± 1) × 102 sec−1, kz = (1.5 ± 0.5) × 102 sec−1, Ax:Ay:Az ≃ 0.56:0.31:0.13, W = (1.7 ± 0.4) × 103 sec−1 for H2T(P‐Me)PP.

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Electron spin polarization in the photoexcited triplet state of porphyrins

Cited by 21 publications

References 10 publications

The Electronic Structure of the Photoexcited Triplet State of Free-Base (Tetraphenyl)porphyrin by Time-Resolved Electron−Nuclear Double Resonance and Density Functional Theory

The Electronic Structure of the Photoexcited Triplet State of Free-Base (Tetraphenyl)porphyrin by Time-Resolved Electron−Nuclear Double Resonance and Density Functional Theory

Triplet state magnetic resonance and fluorescence spectroscopy of metal-substituted hemoglobins

Kinetic Study of the Photoexcited Triplet State of Free Base Porphyrins by EPR

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