Axial coordinated manganese porphyrin/tetraazaporphyrin-4-(10-phenylanthracen-9-yl)pyridine dyads: self-assembly, structure and spectral properties in ground and excited states.

Self-assembly of new donor-acceptor systems based on (5,10,15,20-tetraphenylporphinato)manganese(III)/(5,10,15,20-tetra-4-tert-butylphenylporphinato)manganese(III)/(octakis(4-tert-butylphenyl)tetraazaporphinato)manganese(III) acetate ((AcO)MnTPP/(AcO)MnTBPP/(AcO)MnTAP) and 4-(10-phenylanthracen-9-yl)pyridine (PyAn) was studied using fluorescence spectroscopy and mass spectrometry. It was found that the coordination complexes of 1:1 composition (dyads) are formed in toluene. The spectral properties, the chemical structures and redox behavior of the dyads were described using 1H NMR, IR, EPR spectroscopy and cyclic voltammetry, respectively. The dynamic processes and the characteristics in the excited state of the dyads were obtained using the femtosecond transient absorption spectroscopy method. Density functional theory (DFT), time-dependent DFT methods were used to elucidate the dyad electronic structures and to establish the differences in their frontier molecular orbitals. The analysis of the lambda parameter and the distance of hole-pair interaction was indicated more favorable charge transfer between the macrocycle and the axial PyAn fragment in (AcO)(PyAn)MnTAP. The calculated values of the zero-field splitting parameters D and E/D, together with the g tensors of the lowest spin-orbit state for (AcO)MnTPP and (AcO)(PyAn)MnTPP were obtained using the combination of DFT and Multireference Perturbation Theory (CASSCF/NEVPT2) simulations. The data obtained develop the fundamental basis in the field of photovoltaics and show the prospects for the study of molecular systems of this class.

Facile approach to N,O,S-heteropentacycles via condensation of sterically crowded 3H-phenoxazin-3-one with ortho-substituted anilines.

A convenient method for the synthesis of a series of 2-(arylamino)-3H-phenoxazin-3-ones based on the nucleophilic substitution reaction between sterically crowded 3H-phenoxazin-3-one and arylamines performed by short-term heating of the melted reactants at 220-250 °C is described, and the compounds were characterized by means of single-crystal X-ray crystallography, NMR, UV-vis, and IR spectroscopy, as well as cyclic voltammetry. The reaction with o-amino-, o-hydroxy-, and o-mercapto-substituted arylamines widened the scope and provided an access to derivatives of N,O- and N,S-heteropentacyclic quinoxalinophenoxazine, triphenodioxazine and oxazinophenothiazine systems.

Copper(II) coordination compounds based on bis-hydrazones of 2,6-diacetylpyridine: synthesis, structure, and cytotoxic activity.

By reacting a series of 2,6-diacetylpyridine bis-hydrazones containing pyrimidine (H2L1), benzimidazole (H2L2) and phthalazine (H2L3) heterocyclic fragments with copper(II) chloride and bromide, a variety of pentacoordinated complexes of the composition [Cu(H2L1)X]X, [Cu(HL2)X] and [Cu(HL3)X], where X = Cl-, Br-, are formed. The properties and structure of the compounds were studied by means of NMR, IR, UV-vis, ESR, and X-ray absorption spectroscopy, cyclic voltammetry and X-Ray single crystal diffraction methods. It was shown that complexes of the cationic type [Cu(H2L1)X]X have an asymmetric structure with a distorted square-pyramidal geometry of the coordination unit. The coordination polyhedron of metal chelates [Cu(HL2)X] and [Cu(HL3)X] is an almost ideal square pyramid. Investigations of the cytotoxic activity of the obtained compounds in vitro on human hepatocellular carcinoma (HepG2) and non-tumor human lung fibroblast (MRC-5) cell lines demonstrated that complexes show higher activity compared with the well-known anticancer agent cisplatin. In addition, metal chelates [Cu(H2L1)Cl]Cl, [Cu(HL2)Cl], [Cu(HL2)Br] and [Cu(HL3)Cl] were less toxic to non-tumor cells MRC-5. A study of the binding of complexes to bovine serum albumin (BSA) protein using fluorescence spectroscopy showed that copper complexes are strongly bound to BSA. To study the mechanism of interaction of the complexes with the DNA of cancer cells, molecular dynamics simulation of the compound [Cu(HL3)Cl] was carried out. It was shown that the complex enters into π-stacking interactions predominantly with adenine and thymine bases.

A new heteropentacyclic system via coupling sterically crowded o-benzoquinone with o-phenylenediamines.

The reaction between 3,5-di(tert-butyl)-o-benzoquinone 1 and o-phenylenediamine performed under oxidative conditions that is highly sensitive to the reaction conditions (type of solvent, ratio of reactants, and duration of the reaction) gives rise to various derivatives of a new condensed 10H-quinoxalino[3,2,1-kl]phenoxazin-10-one heteropentacyclic system. The reaction of 1 with N-phenyl-o-phenylenediamine results in the formation of three phenazine-like compounds and, unexpectedly, a derivative of a new spiro[1,3]dioxole-2,2'-furanyl-1H-benzo[d]imidazole system. The molecular structures of the prepared compounds were authenticated by NMR, mass spectra and X-ray crystallography data.

Charge Transfer Complexes Formed by Heterocyclic Thioamides and Tetracyanoethylene: Experimental and Theoretical Study.

Tetracyanoethylene (TCNE) as one of the most versatile organic compounds is involved in various chemical reactions with electron transfer. Charge transfer complexes (CTCs) of a few antioxidants, nitrogen containing thioamides [pyrrolidine-2-thione (I), 1,3-H-imidazolidine-2-thione (II), 1,3-H-Imidazoline-2-thione (III), pyridine-2-thione (IV), 5-trifluoromethylpyridine-2-thione (V), 4-trifluoromethylpyrimidine-2-thione (VI), quinoline-2-thione (VII), 3,4,5,6-tetrahydropyrimidine-2-thione (VIII)] as π-donors and TCNE as π-acceptor were studied. The DFT PCM/UB3LYP/6-31++G(d,p) and SA-CASSCF quantum chemical calculations were used to study the structures and relative stabilities of these complexes in the ground and lowest excited electronic states. The formation of a weak molecular associates in the chloroform and acetonitrile solutions was confirmed by UV/vis and IR absorption spectroscopy. The stability constants and molar extinction coefficients were estimated by UV/vis spectroscopy. The highest stability in acetonitrile is found for associates formed by quinoline-2-thione and pyridine-2-thione with TCNE, the lowest one is found for CTC formed by imidazolidine-2-thione. Molecular associate formed by pyridine-2-thione and TCNE has the greatest stability in the chloroform solution. 5-Trifluoromethylpyridine-2-thione and 4-trifluoromethylpyrimidine-2-thione do not form CTC in CH3CN due to the presence of an electron acceptor group in the molecules. The molar extinction values of CTC vary within the range of 0.4 × 103 to 1.0 × 104 M-1 cm-1. An analytical strategy of thioamides identification based on wavelength and intensity of CTCs absorption band has been suggested.

Synthesis, molecular and electronic structures of six-coordinate transition metal (Mn, Fe, Co, Ni, Cu, and Zn) complexes with redox-active 9-hydroxyphenoxazin-1-one ligands.

A series of pseudo-octahedral metal (M = Mn, Fe, Co, Ni, Cu, Zn) complexes 4 of a new redox-active ligand, 2,4,6,8-tetra(tert-butyl)-9-hydroxyphenoxazin-1-one 3, have been synthesized, and their molecular structures determined with help of X-ray crystallography. The effective magnetic moments of complexes 4 (M = Mn, Fe, Co, and Ni) measured in the solid state and toluene solution point to the stabilization of their high-spin electronic ground states. Detailed information on the electronic structure of the complexes and their redox-isomeric forms has been obtained using density functional theory (DFT) B3LYP*/6-311++G(d,p) calculations. The energy disfavored low-spin structures of manganese, iron, and cobalt complexes have been located, and based on the computed geometries and distribution of spin densities identified as Mn(IV)[(Cat-N-SQ)](2), Fe(II)[Cat-N-BQ)](2), and Co(II)[Cat-N-BQ)](2) compounds, respectively. It has been shown that stabilization of the high-spin structures of complexes 4 (M = Mn, Fe, Co) is caused by the rigidity of the molecular framework of ligands 3 that sterically inhibits interconversions between the redox-isomeric forms of the complexes. The calculations performed on complex 4 (M = Co) predict that a suitable structural modification that might provide for stabilization of the low-spin electromeric forms and create conditions for the valence tautomeric rearrangement via stabilization of the low-spin electromer and narrowing energy gap between the low-spin ground state tautomer and the minimal energy crossing point on the intersection of the potential energy surfaces of the interconverting structures consists in the replacement of an oxygen in the oxazine ring by a bulkier sulfur atom.