Absorption spectra of solutions of tetraphenylporphin and its derivatives in concentrated sulfuric acid

Gnedin, B. G.; Shchukina, M. V.; Morozov, V. V.; Berezin, B. D.; Semeikin, А. S.

doi:10.1007/bf00659717

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“…An alternative explanation would be protonation in the β-positions of the pyrrole ring. However, TSPP 4- , as well as several other FB TPP compounds bearing electron withdrawing substituents in the phenyl ring para -position, do not show any evidences of formation of proton adducts in the β-positions of the pyrrole ring . Bathochromic shifts up to 70 nm are characteristic for the latter type of adducts, and this large shift was not found upon pH decrease in H 2 TSPC 2- solutions.…”

Section: Resultsmentioning

confidence: 80%

Acid−Base Equilibria in 5,10,15,20-Tetrakis(4-sulfonatophenyl)chlorin: Role of Conformational Flexibility

Kruk¹,

Braslavsky²

2006

J. Phys. Chem. A

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The acid−base equilibria in 5,10,15,20-tetrakis(4-sulfonatophenyl)chlorin were studied in aqueous solution and compared with the respective data for the corresponding porphyrin. The reduction of the pyrrole ring in the tetrapyrrolic macrocycle noticeably influences both free base/monoprotonated and mono-/diprotonated species equilibria. In strong acidic solutions protonation of 4-sulfonatophenyl groups takes place in addition to protonation of the macrocycle core. The photophysical properties of all ionic forms are influenced by an enhanced rate of internal S1 → S0 conversion, leading to about 50% and 90% deactivation through this channel for the free base and diprotonated species, respectively. The enhancement of the rate of the radiationless transitions is explained by an increased conformational flexibility of the chlorin macrocycle with respect to that of a porphyrin. Structural volume change measurements with laser-induced optoacoustic spectroscopy support this explanation. The contraction upon triplet state formation of the free base is about one-half of that measured for the corresponding porphyrin. This contraction should be due to intramolecular structural rearrangements of the macrocycle to adopt a minimum energy conformation in case of the chlorin. On the contrary, for the more rigid porphyrin macrocycle the interactions of the molecule with the solvent environment play a more important role. The diprotonated forms of both porphyrin and chlorin show a high radiationless S1 → S0 conversion rate and seem to have a similar conformational flexibility. In agreement with previous calculations, the conformational flexibility of the diprotonated forms appears to be higher than that of the free base molecule.

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Section: Resultsmentioning

confidence: 80%