Search

Acid-base properties of Al(III), Ga(III), and In(III) complexes with tert-butyl-substituted thianaphthene-annulated porphyrazine and tetra(2,3-pyrazino)porphyrazine in proton-donor medium (CHCl-CFCOOH) were studied by spectrophotometric titration. The concentration stability constants of the singly protonated complexes were determined. The effects of the metal nature and aromatic heterocyclic fragment on the basicity of meso-nitrogen atoms were analyzed. Negative inductive effect of the sulfur atom in the thianaphthene fragment reduces the basicity of the meso-nitrogen atoms as compared to analogous porphyrazine and phthalocyanine complexes. Acid-base transformations of the thianaphthene-annulated tetra(2,3-pyrazino)porphyrazine involve both meso-nitrogen atoms and those in the pyrazine rings. [ABSTRACT FROM AUTHOR]

We have performed complex experimental and theoretical investigations of the spectral-luminescent properties and electronic structure of new phthalocyanine analogs, Mg octaphenylporphyrazine and its derivatives with an annulated thiadiazole or selenadiazole ring instead of two phenyl groups. Fluorescence characteristics have been determined at 293 and 77 K: emission, excitation, and fluorescence polarization spectra; fluorescence quantum yield φ, and lifetime τ. Annulation of a five-membered chalcogen-containing heterocycle leads to splitting of the long-wavelength absorption band Q(0-0) and to the bathochromic shift of its longest wavelength component Q(0-0), which increase upon passage from S to Se. At the same time, the fluorescence quantum yield φ and lifetime τ decrease, which is related to the intramolecular heavy-atom effect. The geometric structure of the ground state of the Mg porphyrazine molecules has been determined based on the density functional theory (DFT), and excited electronic states have been calculated with modified parametrization of the INDO/S method, INDO/Sm. Semiquantitatively, the calculated level positions of the lowest Q states and spectral shifts of Mg octaphenylporphyrazine and S-derivative agree with experimental data. For the range of the Soret band, calculated transition energies and their intensity distributions substantially depend on the dihedral angle γ between a phenyl ring and porphyrazine macrocycle. We show that, based on calculations at the angle γ = 60°, bands in the observed absorption spectra can be assigned with an accuracy of ∼2000 cm. [ABSTRACT FROM AUTHOR]

Quantum-chemical calculations for series of porphin (H2P) and porphyrazine (H2PA) derivatives whose molecules contain a 3,4-annulated five-membered heteroaromatic ring of pyrrole, furan, and thiophene as well as 1,2,5-triazole, 1,2,5-oxadiazole, and 1,2,5-thiadiazole have been carried out by the AM1 and INDO/Sm methods (m means “modified parametrization”). As follows from the unrestricted Hartree-Fock AM1 calculations, the ground state energy of the a isomer is lower than that of the b isomers for all compounds, the a and b isomers being NH isomers with the additional five-membered ring fused to a pyrrolenine or pyrrole ring, respectively. Condensation of the five-membered ring for the b isomers of the H2P derivatives is shown to extend the main conjugation path from 18-membered to 21-membered cyclopolyene. However, the 18-membered cyclopolyene for the a isomers of the H2P derivatives and 16-membered cyclopolyene for both isomers of the H2PA derivatives prove to be isolated from the five-membered ring carrying six π-electrons. Based on INDO/Sm computations of electronic absorption spectra of the H2P and H2PA derivatives, it is shown that the Qx level of the a isomers is sensitive to the nature of the annulated ring whereas the Qy level is practically not shifted. On the contrary, the Qx level of the b isomers is relatively insensitive to the nature of the annulated ring while the Qy level decreases monotonously in the H2P and H2PA series, being the first excited state level for the majority of the derivatives (X is along the NH-HN axis; Y, perpendicular to it). The electronic absorption spectra at the border of the visible and near-UV regions are determined mainly by two high-intensity G → Bx and G → By transitions for the H2P derivatives. However, four intense G → Bx, G → By, G → Nx, and G → Ny transitions are characteristic of the spectra of the H2PA derivatives. [ABSTRACT FROM AUTHOR]