Abstract
The electronic and molecular structures of metal-free tetrabenzoporphyrin (H2TBP) and its complexes with zinc, cadmium, aluminum, gallium and indium were investigated by density functional theory (DFT) calculations with a def2-TZVP basis set. A geometrical structure of ZnTBP and CdTBP was found to possess D4h symmetry; AlClTBP, GaClTBP and InClTBP were non-planar complexes with C4v symmetry. The molecular structure of H2TBP belonged to the point symmetry group of D2h. According to the results of the natural bond orbital (NBO) analysis, the M-N bonds had a substantial ionic character in the cases of the Zn(II) and Cd(II) complexes, with a noticeably increased covalent contribution for Al(III), Ga(III) and In(III) complexes with an axial –Cl ligand. The lowest excited states were computed with the use of time-dependent density functional theory (TDDFT) calculations. The model electronic absorption spectra indicated a weak influence of the nature of the metal on the Q-band position.
Highlights
Tetrapyrrole macroheterocycles, such as porphyrines, phthalocyanines and their analogies and metal complexes, have found a number of applications [1,2,3,4]
We describe the influence of the molecular and electronic structures on the properties of the series of tetrabenzoporphyrin complexes
All calculated metal complexes had a fourth order symmetry axis: planar (D4h ) zinc (ZnTBP) and cadmium (CdTBP) complexes, whereas non-planar with doming-distorted porphyrin skeleton (C4v ) complexes of aluminum, gallium and indium comprised a chlorine as an axial ligand (AlClTBP, GaClTBP и InClTBP)
Summary
Tetrapyrrole macroheterocycles, such as porphyrines, phthalocyanines and their analogies and metal complexes, have found a number of applications [1,2,3,4]. The central metal in porphyrins often determines the ratio of the competing fluorescence processes, and internal conversion processes, i.e., efficiency of the singlet oxygen generation. In this regard, along with Zn(II), complex macrocycles containing other heavy metal ions, such as Ga(III) and In(III), are very perspective as photosensitizers. The properties of Ca(II), Zn(II) Y, La, Lu, metal-free tetra(1,2,5thiadiazole)porphyrazine [26,27,28], and other analogies of porphyrins, were investigated by quantum chemical calculations. The lowest excited states were calculated in order to explain the peculiarities and tendencies observed in the experimental electronic absorption spectra available for the Zn, Cd and metal-free tetrabenzoporphyrins
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