Preparation, optical and electrochemical properties, and molecular orbital calculations of tetraazaporphyrinato ruthenium (II) bis(4-methylpyridine) fused with one to four diphenylthiophene units

• Low-symmetrical tetraazaporphyrins were prepared by the reaction of Diphenyldicyanothiophene, phthalonitrile, RuCl3, and methylpyridine.
• Optical and electrochemical properties of the products were examined by UV–vis and MCD spectroscopy, together with cyclic voltammetry.
• Increasing the number of fused thiophene rings affected the 1H NMR spectra, the Q band in the UV–vis spectra, and the first oxidation potentials.
• The optimized structures were utilized to calculate the NMR shielding constants, the HOMO and LUMO orbital energies, and the absorption spectra.

2,5-Diphenyl-3,4-dicyanothiophene (1) and phthalonitrile (2) were mixed and treated with ruthenium (III) trichloride, 4-methylpyridine, and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in 2-ethoxyethanol at 135 °C, to produce low-symmetrical tetraazaporphyrins (TAPs) (3), (4), (5), and (6) with one to three thiophene rings. Two thiophene-annelated tetraazaporphyrins were isolated as opposite and adjacent isomers 4 and 5. The structure of 3 was determined by X-ray crystallography, showing that the thiophene ring linked at the 3,4-positions on the tetraazaporphyrin scaffold deviates from the mean plane of the four central pyrrole nitrogen atoms (N1–N3–N5–N7). Optical and electrochemical properties of the products were examined by UV–vis and magnetic circular dichroism (MCD) spectroscopy, together with cyclic voltammetry. In the 1H NMR spectra, the signals of 4-methylpyridine coordinating to the central ruthenium atom appeared at a higher magnetic field than those of uncoordinated 4-methylpyridine itself due to the shielding effect of the TAP ring. Increasing the number of fused thiophene rings resulted in 1) lower magnetic field shifts of the signals of axially coordinated 4-methylpyridine in the 1H NMR spectra, 2) lower energy shifts of the Q band absorption in the UV–vis spectra, and 3) decreasing (cathodic shift) of the first oxidation potentials. The structures of simplified model compounds were optimized using the DFT method with the Gaussian 09 program at the B3LYP/LANL2DZ level for the Ru atom and the B3LYP/6-31G (d, p) level for the C, H, N, and S atoms. The optimized structures were utilized to calculate the NMR shielding constants, the HOMO and LUMO orbital energies, and the electronic absorption spectra.

Ruthenium complexes of diphenylthiophene-fused low-symmetrical phthalocyanine analogues have been synthesized and characterized and their optical and electrochemical properties examined by electronic absorption, magnetic circular dichroism spectroscopy, and redox potential measurements. These properties were interpreted by the help of molecular orbital (MO) calculations.Figure optionsDownload as PowerPoint slide