Photochemistry of tetrapyrrole complexes

Šíma, Jozef

doi:10.1007/bfb0111332

Cited by 13 publications

(9 citation statements)

References 231 publications

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“…Besides these examples in nature, metalloporphyrins proved to be important complexes in artificial systems, due to their special photophysical, photochemical and redox behaviour. [3][4][5][6][7] Excited state properties of metalloporphyrins are exploited, for example, in optical sensors, 8,9 photodynamic therapy, 10-12 photocatalysis, 13-17 and artificial photosynthesis. 18 Most metalloporphyrins contain a metal ion in the center of the planar tetrapyrrolic ring system.…”

Section: Introductionmentioning

confidence: 99%

Photophysics and photochemistry of water-soluble, sitting-atop bis-thallium(I) 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin

Valicsek¹,

Horváth²,

Stevenson³

2004

Photochem Photobiol Sci

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In aqueous solutions, thallium(I) ions and 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin form a kinetically labile metalloporphyrin of 2 : 1 composition (Tl(2)P(4-)). The formation constant of this sitting-atop (SAT) complex is relatively low (beta2/[H+]2= 3.55 x 10(3) M(-2) at pH = 7), due to the large size and rather small charge of Tl+. As a consequence of the considerably weak metal-ligand interaction in this system, the 1 : 1 species does not appear in detectable concentration. Both the absorption and the emission properties of the Tl(2)P(4-) complex are characteristic for the typical SAT metalloporphyrins. Compared to the corresponding values of the free-base porphyrin, the diminished fluorescence quantum efficiency (Qfl= 0.0131 vs. 0.056) of Tl(2)P(4-) can be accounted for by the heavy-atom effect, while the larger Stokes shift (442 vs. 282 cm(-1)) indicates a stronger distortion of the ligand plane. Both Soret- and Q-band irradiations of the Tl(2)P(4-) complex lead to the degradation of the porphyrin with quantum yields of magnitude 3 x 10(-4). The primary photochemical step in this process is ligand-to-metal charge transfer reaction, which is unusual for normal (coplanar) metalloporphyrins. In the case of SAT complexes, the kinetic lability facilitates the separation of the primary redox products, followed by an irreversible ring-opening of the oxidized porphyrin. Photoinduced electron ejection as a considerable step in the degradation mechanism could be ruled out.

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Section: Introductionmentioning

confidence: 99%

Photophysics and photochemistry of water-soluble, sitting-atop bis-thallium(I) 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin

Valicsek¹,

Horváth²,

Stevenson³

2004

Photochem Photobiol Sci

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“…The roles of natural metalloporphyrins are very important in various biological systems such as electron transfer catalysts of heme-containing enzymes, active sites in heme proteins which reversibly bind dioxygen and carbon monoxide, and the light-harvesting pigments in photosynthetic processes. The photochemistry of synthetic metalloporphyrins has been extensively investigated to elucidate the biological functions of natural metalloporphyrins . Photochemical processes such as photoinduced ligand dissociation are strongly linked with various photophysical processes of the excited-state molecules as luminescence, internal conversion, intersystem crossing, and intramolecular energy dissipation processes.…”

Section: Introductionmentioning

confidence: 99%

Laser Photolysis Studies of the Photochemical Reactions of Chromium(III) Octaethylporphyrin and Tetramesitylporphyrin Complexes in Toluene Solution

et al. 2003

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A nanosecond laser photolysis study was carried out for the Cr(III) porphyrin complexes of 2,3,7,8,12,13,17,18-octaethylporphyrin, [Cr(OEP)(Cl)(L)], and of 5,10,15,20-tetramesitylporphyrin, [Cr(TMP)(Cl)(L)], in toluene containing water and an excess amount of L (L = axial ligand). The laser photolysis generates the triplet excited state of the parent complex as well as a five-coordinate complex, [Cr(porphyrin)(Cl)], produced by the photodissociation of the axial ligand L. The yields for the formation of the triplet state and the photodissociation of L are found to markedly depend on the nature of both L and porphyrin ligand. The five-coordinate [Cr(porphyrin)(Cl)] readily reacts with both H(2)O and L in the bulk solution to give [Cr(porphyrin)(Cl)(H(2)O)] and [Cr(porphyrin)(Cl)(L)], respectively. The axial H(2)O ligand in [Cr(porphyrin)(Cl)(H(2)O)] is then substituted by the ligand L to regenerate the original complex [Cr(porphyrin)(Cl)(L)]. In principle, the substitution reaction takes place by the dissociative mechanism: the first step is the dissociation of H(2)O from [Cr(porphyrin)(Cl)(H(2)O)], followed by the reaction of the five-coordinate [Cr(porphyrin)(Cl)] with the ligand L to regenerate [Cr(porphyrin)(Cl)(L)]. The rate constants for this ligand substitution reaction are found to exhibit bell-shaped ligand concentration dependence. The detailed kinetic analysis revealed that both ligands L and H(2)O in toluene make a hydrogen bond with the axial H(2)O ligand in [Cr(porphyrin)(Cl)(H(2)O)] to yield dead-end complexes for the substitution reaction. The reaction mechanisms are discussed on the basis of the substituent effects of the porphyrin peripheral groups and the kinetic parameters determined from the temperature dependence of the rate constants.

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“…(8) They are related to the origin of sediments (9) and to poisoning of catalysts used in oil processing. Porphyrins with specific structures can also be prepared in the laboratory for use as catalytic agents, (10,11) photosensitive and optical materials, (12)(13)(14) molecular switches, (15) and in medical treatment and mimetic studies. (16,17) Even though such molecules are very important in so many chemical processes, insufficient thermochemical studies on porphyrins have been performed.…”

Section: Introductionmentioning

confidence: 99%

The standard molar enthalpies of formation of 5,10,15,20-tetraphenylporphine and 5,10,15,20-tetrakis(4-methoxyphenyl)porphine by oxygen bomb combustion calorimetry

Patiño

Torres

Norzagaray-Campos

1999

The Journal of Chemical Thermodynamics

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Photochemistry of tetrapyrrole complexes

Cited by 13 publications

References 231 publications

Photophysics and photochemistry of water-soluble, sitting-atop bis-thallium(I) 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin

Photophysics and photochemistry of water-soluble, sitting-atop bis-thallium(I) 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin

Laser Photolysis Studies of the Photochemical Reactions of Chromium(III) Octaethylporphyrin and Tetramesitylporphyrin Complexes in Toluene Solution

The standard molar enthalpies of formation of 5,10,15,20-tetraphenylporphine and 5,10,15,20-tetrakis(4-methoxyphenyl)porphine by oxygen bomb combustion calorimetry

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