Spectral peculiarities of NH-tautomerism in isocycle-containing porphyrins and their covalently linked dimers

Zenkevich, É. I.; Шульга, А. М.; Chernook, A. V.; Gurinovich, G. P.

doi:10.1016/0009-2614(84)85740-1

Cited by 24 publications

(12 citation statements)

References 3 publications

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“…A value of ∼104 s -1 was found for the β-substituted porphyrins in the ground state at 292 K, and most likely a value of the same order applies to the tautomeric exchange rate constant for the S 1 state of β-substituted porphyrins. To some extent, this is supported by literature data, − where different fluorescence spectra were found for two NH tautomers at room temperature for a series of asymmetrically substituted free base porphyrins, including the β-tetra-substituted compound 2,3,12,13-tetraethylporphyrin. The observed biexponential fluorescence decay in all the solvents used (except DMF) may be also considered as evidence for the coexistence of two tautomers of H 2 TPP−NO 2 that are not in equilibrium on the time scale of the fluorescence lifetimes (see below).…”

Section: Discussionsupporting

confidence: 82%

On the Nature of the Fluorescent State in β-Nitrotetraarylporphyrins

et al. 1998

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2-NO 2 -5,10,15,20-tetraphenylporphyrin (H 2 TPP-NO 2 ) is shown to exist in solution as an equilibrium mixture of two NH tautomers with different spectral and photophysical properties. At 77 K in a rigid glass solution the fluorescence spectra of the tautomers contain two well-resolved narrow bands that are slightly (∼300 cm -1 ) Stokes-shifted with respect to the corresponding Q X00 absorption bands, with the spectrum of the more stable tautomer being ∼500 cm -1 red-shifted as compared to the spectrum of the less stable tautomer. At room temperature, the tautomers show almost identical broad and structureless fluorescence spectra, markedly red-shifted relative to the longest wavelength absorption band. The Stokes shift increases with an increase of solvent polarity, being as large as ∼2000 cm -1 in N,N-dimethylformamide. Fluorescence lifetimes of the tautomers are found to be markedly (about a factor of 2) different, with both decreasing with an increase of solvent polarity. The reasons for these peculiar fluorescence properties can be understood on the basis of semiempirical quantum chemical calculations. Charge-transfer (CT) states are found to be located between the porphyrinic Q and B states for both tautomers, and a different energy of the CT states gives rise to different fluorescence lifetimes of the tautomers. The calculations also predict a lowering of the Q X state energy and an increase of its dipole moment µ with a decrease of the angle θ between the plane of the NO 2 group and the porphyrin plane (relative to the ground-state equilibrium geometry with θ ) 80°). We suggest that, in solution, such an increase in the µ value should result in an increase of the stabilization interaction between the polar porphyrin and solvent molecules and, consequently, in flattening of the Q X state energy curve as a function of θ and a shift of the minimum of this curve to θ values less than 80°. Both quantum chemical calculations and picosecond transient absorption measurements of the S 1 f S n absorption show that the fluorescent Q X state of H 2 TPP-NO 2 has mainly 1 (π,π*) character with a relatively small charge-transfer admixture.

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Section: Discussionsupporting

confidence: 82%

On the Nature of the Fluorescent State in β-Nitrotetraarylporphyrins

et al. 1998

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“…The theoretical and experimental investigations of inner proton migration in porphyrins in their electronic ground state have shown that this process is strongly temperature dependent. 21,[46][47][48] This is easy to understand, if one takes into account the existence of a potential barrier between two configurations of the inner N-bound hydrogen atoms. As result, the equilibrium tautomer concentration changes with changing the solution temperature: the equilibrium shifts to the tautomer with lower energy of the ground state when temperature is lowered.…”

Section: Resultsmentioning

confidence: 98%

“…NH-tautomerism of symmetrical porphyrins can be studied at very low temperatures in Shpol'ski or rare gas matrices under spectrally selective laser excitation only. 19,20 In the case of porphyrins with nonsymmetrical substitutions, it has been shown, 21,22 that the spectral separation between absorption bands of lowest energy for two NH-tautomers has a value of about 300 cm -1 . At the same time, the fluorescence spectrum of each tautomer were possible to resolve only at 77 K. Moreover, there is a gap in knowledge about the influence of NH-tautomerism of nonsymmetrical porphyrins on probabilities of radiative and nonradiative deactivation pathways of the excited states.…”

Section: Introductionmentioning

confidence: 98%

Novel cycloketo tetraphenylporphyrins: spectroscopic study of structure-properties relationships

Ermilov

Jasinski

Jux

et al. 2008

Linear and Nonlinear Optics of Organic Materials VIII

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The developments in porphyrin chemistry over the last decades give great advantages for the practical use of porphyrin-based compounds. The properties of these compounds can be systematically tuned by rational utilization of substituents on meso-and/or β-positions as well as by using different metal atoms in the center of the tetrapyrrole macrocycle.Recently we prepared novel mono-and bis-functionalized cycloketo-porphyrins (CKPors). In this work the results of detailed spectroscopic investigations of these compounds are presented. It was found that a seven-membered ketone exocycle remarkably influences the photophysical properties of the CKPor systems. For mono-functionalized CKPors it results in strongly enhanced probability of intersystem crossing S 1 → T 1 with an ISC quantum yield up to 90 %. Moreover, the absorption of all CKPors undergoes a bathochromic shift and the Q-bands extinction is above two times higher compared to that of H 2 TPP, what makes these compounds promising candidates for use as photosensitizers in photodynamic therapy of tumors.For the first time two NH-tautomers of nonsymmetrical CKPors were experimentally resolved at room temperature using optical spectroscopic methods. It was found that the concentration of tautomer A with a lower frequency of the S 0,0 → S 1,0 transition is higher than that one of tautomer B at room temperature, and becomes dominant with cooling down. In contrast -and as it is expected -only one optical active species was observed for nonsymmetrical CKPor with a central Zn(II) atom as well as for symmetrical bis-CKPor.

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“…Stepanov Institute of Physics, National Academy of Sciences of Belarus (Minsk) and described in details together with their optical properties in our earlier publications. In this paper, the subject of the discussion will be the dimers in which tetrapyrrolic subunits are covalently linked via spacers of various nature: i) ethane-bisporphyrins with a single -CH 2 -CH 2 -via meso-positions, [34,[61][62][63][64][65][66][67] ii) cyclodimers where cyclopentaneporphyrin molecules are coupled via isocycles, [68][69][70][71][72][73] and iii) chemical dimers of octaethylporphyrins with the phenyl bridge via meso-positions. [17,18,27,[74][75][76] It should be noted that in order to clarify spectral-kinetic properties that are characteristic for the dimers namely, we have especially prepared and characterized the precursor monomeric species with side substituents of the same nature and in the same positions like the corresponding spacers.…”

Section: Methodsmentioning

confidence: 99%

“…Heterodimers containing a Cu ion in the center of one subunit have some general features. [62][63][64][65][66][67][68][69][70] In the case of the heterodimers (H 2 P+Cu)(OEP) 2 and (Zn+Cu)(OPP) 2 the emission belongs to the H 2 -or Zn-subunit, but is drastically quenched (j/ j 0 ≈40, Table 1). The singlet-singlet ET from Cu-subunit to H 2 -or Zn-subunit having a S 0 -S 1 transitions is not detected, and, additionally, the lifetime of the T 1 state (t T ) of H 2 -or Zn-subunits is decreased in these heterodimers compared to the corresponding homodimers without Cu-porphyrins.…”

Section: Deactivation Of Excited States In Nanostructures Containing mentioning

confidence: 99%

Deactivation of Excited States in Nanostructures Containing Cu-Porphyrin Subunit

Zenkevich¹

2016

MHC

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Here, we present a semi-review of mutual Belarussian-German collaboration Ключевые слова: Порфирины, химические димеры порфиринов, самоорганизованные мультипорфириновые комплексы, полимерные упорядоченные хлорофилловые агрегаты, наноансамбли на основе полупроводни-ковых квантовых точек, дезактивация синглетных и триплетных возбужденных состояний, перенос энергии/ электрона.

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Spectral peculiarities of NH-tautomerism in isocycle-containing porphyrins and their covalently linked dimers

Cited by 24 publications

References 3 publications

On the Nature of the Fluorescent State in β-Nitrotetraarylporphyrins

On the Nature of the Fluorescent State in β-Nitrotetraarylporphyrins

Novel cycloketo tetraphenylporphyrins: spectroscopic study of structure-properties relationships

Deactivation of Excited States in Nanostructures Containing Cu-Porphyrin Subunit

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