Electronic structure and photophysics of the aza-analogues of hydroporphyrins

Kuzmitsky, V. A.; Макарова, Е. А.; Першукевич, П. П.; Shushkevich, I. K.; Solovyov, K. N.; Tusov, V.B.

doi:10.1016/j.chemphys.2003.10.039

Cited by 31 publications

(60 citation statements)

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“…reproduced correctly in the calculations by the CNDO/S method [11][12][13][14][15] as well as in the earlier calculations by the PPP method [16][17][18]. One of the reasons for this disagreement is the absence of x-ray structural data on H 2 Ch.…”

mentioning

confidence: 75%

“…The CNDO/S data and the data of earlier works [11][12][13][14][15] point to the fact that, in all cases, the Soret band of H 2 Ch is mainly due to two ππ * -transitions: G → B y and G → B x . Unlike this, the Soret band of the H 2 P molecule calculated by the CNDO/S and ab initio methods can be due to two or three ππ * -transitions (see [9]).…”

Section: Rhfmentioning

confidence: 87%

“…It is interesting that free molecules of H 2 Ch are formed as a result of thermal decomposition of H 2 P in vapors at a temperature T = 390 o C [34] and in a supersonic jet flowing out of a nozzle at a temperature T = 370 o C [35]. The data of investigations of H 2 Ch in other media and of some derivatives of H 2 Ch close to it in structure are presented in [7,10,15,17,18,38,[41][42][43][44][45]. As is seen from Table 3, for all the media considered the Q x level of H 2 Ch is shifted relative to the Q x level of H 2 P toward longer waves by δE Q x . -400 to -500 cm -1 .…”

Section: Rhfmentioning

confidence: 99%

“…It should be noted that such restrictions were imposed on the symmetry of the molecule in the RHF ab initio calculations of its ground state [23; 29]; the geometry obtained was then used in the calculations of excited states of H 2 Ch [23,26]. The same restrictions were imposed on the symmetry of the H 2 Ch molecule when its geometry was constructed by the data of x-ray structural analysis [19] and excited states of H 2 Ch were calculated by the CNDO/S semiempirical method [11][12][13][14][15]. It is seen from Fig.…”

Section: Rhfmentioning

confidence: 99%

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Dependence of the Electronic Spectra of the Chlorin Molecule on the Degree of Alternation of the Macrocycle Bond Lengths

Kuz'mitskii

2005

J Appl Spectrosc

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539.19The geometric structure of the chlorin molecule (H 2 Ch) has been calculated by the restricted and unrestricted Hartree-Fock (RHF and UHF) methods with an AM1 Hamiltonian. Transformations of this molecule into excited electronic states have been calculated by the CNDO/S method. The RHF method without symmetry restrictions gives a plane structure for the chlorin macrocycle with an alternation of the lengths of the bonds along the 18-member azacyclopolyene and a C 1h symmetry for the molecule as a whole. The level of the first excited state Q 1 of this structure is substantially shifted (δE Q 1 . +4000 cm -1 ) relative to the Q x level of porphin (H 2 P) toward shorter waves, which is in contradiction with the experimental data, according to which this shift is long-wave and is equal to δE Q x = -400 to -550 cm -1 . The optimization of the geometry of H 2 Ch by the UHF method has shown that it has a structure with an 18-member azacyclopolyene with bonds of equal lengths and a D 2h symmetry. For this geometry of H 2 Ch the calculated shift of the Q x level, equal to δE Q x = -70 cm -1 , is bathochromic and the position of the Q y level is practically exactly coincident with the experimental one. For the geometry calculated by the RHF method with restrictions on the D 2h symmetry of the 18-member azacyclopolyene δE Q x = +180 cm -1 , and for the geometry calculated with restrictions on the highest C 2v symmetry of the H 2 Ch molecule δE Q x = +620 cm -1 . The latter result shows that the "natural" requirement for the C 2v symmetry of the H 2 Ch macrocycle, which is frequently used in various calculations, is inadequate to achieve a quantitative agreement between the calculation and experimental data and, in this case, the lengths of the bonds along the 18-member azacyclopolyene are not equal. Keywords: chlorin, quantum-chemical calculation, restricted and unrestricted Hartree-Fock methods, AM1 CNDO/S methods.Introduction. It has been established in the calculations of monobenzoporphyrin molecules (H 2 MBP) carried out in [1] that their geometric and chemical structures significantly influence the energy of the Q and B states, the transitions to which determine the positions of the absorption bands in the visible and near-UV regions of the spectrum. The geometric structure of the molecules considered was optimized by the restricted and unrestricted HartreeFock (RHF and UHF) methods with a semiempirical AM1 Hamiltonian [2]. The results obtained have an important peculiarity. The RHF method without symmetry restrictions gives a structure of H 2 MBP with an alternation of the lengths of the bonds along the 18-member azacyclopolyene and large (,0.5 eV) shifts of its Q levels relative to the Q levels of porphin (H 2 P) toward shorter waves. In contrast to this, the UHF method gives an H 2 MBP structure with equal lengths of the bonds along the 18-member azacyclopolyene and long-wave shifts of the Q levels that are consistent in value with the experimental shifts [3].It should be noted that the data of calculations o...

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mentioning

confidence: 75%

Section: Rhfmentioning

confidence: 87%

Section: Rhfmentioning

confidence: 99%

Section: Rhfmentioning

confidence: 99%

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Dependence of the Electronic Spectra of the Chlorin Molecule on the Degree of Alternation of the Macrocycle Bond Lengths

Kuz'mitskii

2005

J Appl Spectrosc

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“…Taking into account configurational interaction (CI) in the relative molecule, i.e., free-base porphyrazine, at the CNDO/S 53 and TDDFT 54 levels of theory also predicts that the lowest gg transition with non-vanishing 2PA strength is of the A g → A g type. The authors 53,54 also found that the one-electron approximation works quantitatively for this particular transition in porphyrazine. Therefore, we assume the A g → A g symmetry for the lowest energy 2PA-allowed transition in both H 2 TtBuPc and H 2 TBTAC.…”

Section: Few Essential States Modelmentioning

confidence: 98%

Alternative selection rules for one- and two-photon transitions in tribenzotetraazachlorin: Quasi-centrosymmetrical π-conjugation pathway of formally non-centrosymmetrical molecule

Makarov

Drobizhev

Wicks

et al. 2013

The Journal of Chemical Physics

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We compare the two-photon absorption (2PA) spectra of non-centrosymmetrical metal-free tribenzotetraazachlorin (H 2 TBTAC) and analogous symmetrical tetra-tert-butyl-phthalocyanine (H 2 TtBuPc). Surprisingly, despite formal lack of center of inversion, the 2PA spectrum of H 2 TBTAC displays a two-photon allowed transition at 935 nm, similar to gerade-gerade (g-g) transitions observed in H 2 TtBuPc and in other symmetrical phthalocyanines. This transition is even better resolved in the singlet-singlet excited-state absorption spectrum. We tentatively explain the survival of the g-g transition in H 2 TBTAC by assuming that the main π -electron conjugation pathway in the tetraazasubstituted tetrapyrrole macrocycle bypasses the outer parts of the two oppositely located isoindole rings and thus renders the optically responsive core of the chromophore quasi-centrosymmetrical. By using the independently measured ground-and excited-state absorption extinction coefficients, we also show that the two-photon absorptivity can be quantitatively explained by a simple threelevel model with the lowest energy Q 1 state serving as an intermediate level.

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Influence of a Solvent on the Quantum Yield and Duration of the Fluorescence of Tetraazoporphin

et al. 2005

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ev UDC 535.37In view of the discrepancies between the values available in the literature for the photophysical parameters of tetraazaporphin in solutions, we measured its quantum yield and duration of fluorescence in a number of solvents. It has been found that alcohols (isobutanol and isopropanol) quench the fluorescence appreciably. For a solution in toluene -a stable chemically inactive and low-polar solvent -the measured quantum yield of the fluorescence of tetraazaporphin is equal to 0.180 ± 0.015 and its duration is 3.4 ± 0.1 nsec.Keywords: tetraazaporphin, quantum yield of fluorescence, fluorescence duration.Introduction. The tetraazaporphin (H 2 TAP) molecule, or porphyrazine, is one of the fundamental structures in the porphin series, which is an intermediate between the biologically important class of porphyrins and classical dyes of the type of phthalocyanine, which are finding wide application in various fields of science and technology.In investigating the effect of hydrogenation of pyrrolic rings in porphyrazine macrocycles on the photophysical properties, in [1, 2] the quantum yield of fluorescence (ϕ F ) of H 2 TAP was measured as a basis for comparison with the data on dihydroderivatives. By comparing our results with the data of earlier investigations [3-6], we found that there were noticeable discrepancies between the values of ϕ F measured by various authors and also between the data on durations of fluorescence τ F . In [3,4], it was found that ϕ F = 0.12 and τ F = 3.7 nsec (see also the review [7]), in [5], ϕ F = 0.16 and τ F = 6.4 nsec; in [6], ϕ F = 0.12. Recently,in [8], the value ϕ F = 0.29 was obtained for H 2 TAP, whereas in [1, 2] ϕ F = 0.19 and τ F = 3.3 nsec.Since different solvents were used in the works cited, the idea arose that the quantity ϕ F of H 2 TAP can substantially depend on the nature of the solvent. The aim of the present work is to elucidate this influence and to arrange in an ordered fashion the data on the values of ϕ F and τ F for H 2 TAP.Experimental. Measurements of the quantum yield of fluorescence were performed by a relative method from the ratio between the areas of the fluorescence spectra of an object and a standard determined in terms of "quantum" intensities (I λ /hν) on an SDL-2 automated spectrofluorimeter (USSR) consisting of an MDR-12 light-transmission excitation monochromator and an MDR-23 registration monochromator. The excitation and registration axes were arranged at an angle of 90 o . A DKsSh-120 xenon lamp was used as the source of excitation. The light signal separated by the monochromator was registered with the aid of an FÉU-100 cooled photomultiplier (spectral range 200-800 nm) operating in the regime of photon counting. The spectral sensitivity of the recording monochromator-FÉU system was corrected with the aid of a TRSh 2850 standard ribbon tungsten lamp. The spectral width of the excitation monochromator slit did not exceed 4.8 nm in the entire spectral range studied, and that of the registration monochromator -2.6 nm in the 400-800-nm ...

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Electronic structure and photophysics of the aza-analogues of hydroporphyrins

Cited by 31 publications

References 43 publications

Dependence of the Electronic Spectra of the Chlorin Molecule on the Degree of Alternation of the Macrocycle Bond Lengths

Dependence of the Electronic Spectra of the Chlorin Molecule on the Degree of Alternation of the Macrocycle Bond Lengths

Alternative selection rules for one- and two-photon transitions in tribenzotetraazachlorin: Quasi-centrosymmetrical π-conjugation pathway of formally non-centrosymmetrical molecule

Influence of a Solvent on the Quantum Yield and Duration of the Fluorescence of Tetraazoporphin

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