Axial Coordinated Manganese(III) 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, ESR 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.

Field induced slow magnetic relaxation in a linear homotrinuclear manganese heterospin coordination compound with S = 7/2 ground state and intriguing spin density distribution.

We report a first example of field-induced (HDC = 2500 Oe) slow magnetization relaxation in the homotrinuclear linear heterospin manganese coordination compound with S = 7/2 ground state, based on the bidentate 3,5-di-tert-butyl-1,2-benzoquinone-1-monooxime (HL) ligand with composition {[MnL3]Mn[MnL3]}.

A novel hybrid protein composed of superoxide-dismutase-active Cu(II) complex and lysozyme.

A novel hybrid protein composed of a superoxide dismutase-active Cu(II) complex (CuST) and lysozyme (CuST@lysozyme) was prepared. The results of the spectroscopic and electrochemical analyses confirmed that CuST binds to lysozyme. We determined the crystal structure of CuST@lysozyme at 0.92 Å resolution, which revealed that the His15 imidazole group of lysozyme binds to the Cu(II) center of CuST in the equatorial position. In addition, CuST was fixed in position by the weak axial coordination of the Thr89 hydroxyl group and the hydrogen bond between the guanidinium group of the Arg14 residue and the hydroxyl group of CuST. Furthermore, the combination of CuST with lysozyme did not decrease the superoxide dismutase activity of CuST. Based on the spectral, electrochemical, structural studies, and quantum chemical calculations, an O2- disproportionation mechanism catalyzed by CuST@lysozyme is proposed.

Quinoid-Thiophene-Based Covalent Organic Polymers for High Iodine Uptake: When Rational Chemical Design Counterbalances the Low Surface Area and Pore Volume.

A novel 2D covalent organic polymer (COP), based on conjugated quinoid-oligothiophene (QOT) and tris(aminophenyl) benzene (TAPB) moieties, is designed and synthesized (TAPB-QOT COP). Some DFT calculations are made to clarify the equilibrium between different QOT isomers and how they could affect the COP formation. Once synthetized, the polymer has been thoroughly characterized by spectroscopic (i.e., Raman, UV-vis), SSNMR and surface (e.g., SEM, BET) techniques, showing a modest surface area (113 m2 g-1) and micropore volume (0.014 cm3 g-1 with an averaged pore size of 5.6-8 Å). Notwithstanding this, TAPB-QOT COP shows a remarkably high iodine (I2) uptake capacity (464 %wt) comparable to or even higher than state-of-the-art porous organic polymers (POPs). These auspicious values are due to the thoughtful design of the polymer with embedded sulfur sites and a conjugated scaffold with the ability to counterbalance the relatively low pore volumes. Indeed, both morphological and Raman data, supported by computational analyses, prove the very high affinity between the S atom in our COP and the I2. As a result, TAPB-QOT COP shows the highest volumetric I2 uptake (i.e., the amount of I2 uptaken per volume unit) up to 331 g cm-3 coupled with a remarkably high reversibility (>80% after five cycles).

Donor-acceptor interactions of gold(III) porphyrins with cobalt(II) phthalocyanine: chemical structure of products, their spectral characterization and DFT study.

In the context of the development of coordination energy-harvesting systems, the axial bonding of cobalt(II) octakis(3,5-di-tert-butylphenoxy)phthalocyanine (1) with gold(III) 2,3,7,8,12,18-hexamethyl,13,17-diethyl,5-(pyridin-4-yl)- and (2,3,7,8,12,18-hexamethyl,13,17-diethyl,5-(pyridin-3-yl)porphin (2 and 3), the structure, the spectral/electrochemical properties of the resulting donor-acceptor complexes and photoinduced electron transfer in them are studied. The process of the dyad formation passing as self-assembly in the donor-acceptor phthalocyanine-porphyrin systems was explored using UV-Visible, IR, and 1H NMR spectroscopy and mass spectrometry. The geometric and electronic structures of the dyads were identified using density functional theory (DFT) and time-dependent DFT calculations. The electron transfer in the coordination complexes studied was confirmed by recording the radical ion pairs namely 1˙+ : 2˙-/1˙+ : 3˙- and measuring the kinetics of the photoinduction and decay of these states by a femtosecond laser photolysis technique. The effect of the gold(III) porphyrin macrocycle nature in the lifetime of radical ion pairs was shown. The redox potential values for the coordination dyads and the photoelectrochemical parameters defining their perspective in design and understanding of PET systems were observed using the cyclic voltammetry/amperometry methods and the short-circuited electrochemical cell Ti|a dyad film|0.5 M Na2SO4|Pt, respectively.

Ultrafast bandgap narrowing and cohesion loss of photoexcited fused silica.

Coupling and spatial localization of energy on ultrafast timescales and particularly on the timescale of the excitation pulse in ultrashort laser irradiated dielectric materials are key elements for enabling processing precision beyond the optical limit. Transforming matter on mesoscopic scales facilitates the definition of nanoscale photonic functions in optical glasses. On these timescales, quantum interactions induced by charge non-equilibrium become the main channel for energy uptake and transfer as well as for the material structural change. We apply a first-principles model to determine dynamic distortions of energy bands following the rapid increase in the free-carrier population in an amorphous dielectric excited by an ultrashort laser pulse. Fused silica glass is reproduced using a system of (SiO4)4- tetrahedra, where density functional theory extended to finite-temperature fractional occupation reproduces ground and photoexcited states. Triggered by electronic charge redistribution, a bandgap narrowing of more than 2 eV is shown to occur in fused silica under geometry relaxation. Calculations reveal that the bandgap decrease results from the rearrangement of atoms altering the bonding strength. Despite an atomic movement impacting strongly the structural stability, the observed change of geometry remains limited to 7% of the interatomic distance and occurs on the femtosecond timescale. This structural relaxation is thus expected to take place quasi-instantly following the photon energy flux. Moreover, under intense laser pulse excitation, fused silica loses its stability when an electron temperature of around 2.8 eV is reached. A further increase in the excitation energy leads to the collapse of both the structure and bandgap.

Topological Quasi-2D Semimetal Co3Sn2S2: Insights into Electronic Structure from NEXAFS and Resonant Photoelectron Spectroscopy.

The electronic structure of the natural topological semimetal Co3Sn2S2 crystals was studied by using near-edge X-ray absorption spectroscopy (NEXAFS) and resonant photoelectron spectroscopy (ResPES). Although, the significant increase of the Co 3d valence band emission is observed at the Co 2p absorption edge in the ResPES experiments, the spectral weight at these photon energies is dominated by the normal Auger contribution. This observation indicates the delocalized character of photoexcited Co 3d electrons and is supported by the first-principle calculations. Our results on the investigations of the element- and orbital-specific electronic states near the Fermi level of Co3Sn2S2 are of importance for the comprehensive description of the electronic structure of this material, which is significant for its future applications in different areas of science and technology, including catalysis and water splitting.

N Basicity of Substituted Fullero[60]/[70]pyrrolidines According to DFT/TD-DFT Calculations and Chemical Thermodynamics.

The basicity thermodynamic parameters of pyridyl/imidazole-substituted fullero[60]/[70]pyrrolidines with respect to N heteroatoms in dichloromethane, which are necessary both to deepen insight into aromaticity "neque levia" and to create supramolecular chemical structures for application, are obtained and discussed in this work. Because of the presence of a chromophore in the molecules, the acid-base reactions of three C60 derivatives functionalized in different ways and one C70 derivative are studied using spectrophotometric titration with trifluoroacetic acid. The dependence of the pK values determined using the data on Hammett's acidity functions, H0, for a binary nonaqueous solvent on the molecule's chemical structure is shown. Density functional theory (DFT) and time-dependent DFT (TD-DFT) at the B3LYP/6-311G(d,p) level were used for the optimization of the fullerene derivative structures and modeling of their UV-vis spectra. The pKBH+ values of substituted fullero[60]/[70]pyrrolidines are predicted by quantum-chemical calculations.

Correlations in the Electronic Structure of van der Waals NiPS3 Crystals: An X-ray Absorption and Resonant Photoelectron Spectroscopy Study.

The electronic structure of high-quality van der Waals NiPS3 crystals was studied using near-edge X-ray absorption spectroscopy (NEXAFS) and resonant photoelectron spectroscopy (ResPES) in combination with density functional theory (DFT) approach. The experimental spectroscopic methods, being element specific, allow one to discriminate between atomic contributions in the valence and conduction band density of states and give direct comparison with the results of DFT calculations. Analysis of the NEXAFS and ResPES data allows one to identify the NiPS3 material as a charge-transfer insulator. Obtained spectroscopic and theoretical data are very important for the consideration of possible correlated-electron phenomena in such transition-metal layered materials, where the interplay between different degrees of freedom for electrons defines their electronic properties, allowing one to understand their optical and transport properties and to propose further possible applications in electronics, spintronics, and catalysis.

A trinuclear nickel(II) Schiff base complex with phenoxido- and acetato-bridges: combined experimental and theoretical magneto-structural correlation.

We describe the synthesis and characterization of a new trinuclear Ni(ii) Schiff base complex of formula [Ni3(L)2(NCS)2(OAc)2(CH3OH)2] (1) where HL is the 1 : 1 condensation product of 2-picolylamine and o-vanillin. The crystal structure of complex 1 shows that the two terminal Ni(ii) ions are connected to the central one through a phenoxido- and a syn-syn acetato bridge, giving rise to a very bent configuration in the Ni3-core. Magnetic susceptibility measurements show the presence of a weak antiferromagnetic coupling with J = -3.22(2) cm-1. We also report a magneto-structural correlation, performed with all the magnetically characterized Ni(ii) trimers with similar bridges, showing a linear dependence between the J value and the dihedral angle (θ) between the planes containing the Ni-O-Ni and the carboxylate bridges. The super-exchange interaction is investigated by extensive density functional calculations within the broken symmetry approximation which show good agreement with the experimental data. The analysis of the spin density distribution and the shape of the magnetically active single occupied molecular orbitals (SOMO) provide a mechanism of exchange coupling through the bridging groups.

DFT Study of the CNS Ligand Effect on the Geometry, Spin-State, and Absorption Spectrum in Ruthenium, Iron, and Cobalt Quaterpyridine Complexes.

Geometry parameters, total energy of the system in different spin states, harmonic vibrational frequencies, and absorption spectra were computed for a range of mononuclear quaterpyridine Ru(II), Fe(III/II), and Co(III/II) complexes with two axial ambidentate CNS ligands by using density functional theory (DFT) and time-dependent DFT calculations. Both structural and electronic properties were found to be correlating with the type of the binding atom in the CNS ligand (isomerization differs by 4-13 kcal·mol-1). The N-bonding of CNS ligands is energetically favored. It was also found that the low spin (LS) state is the ground state for both Ru(II) and Co(III) complexes regardless of the CNS arrangement. The other complexes are the high-spin (HS) ground-state ones with the only exception of the S-bonded CNS isomer of the Fe(III) complex. The dependencies of energy differences between the HS and LS states versus C demonstrated stabilization of the HS state with an increasing amount of the exact exchange admixture (C) for iron and cobalt complexes. An opposite behavior was observed for ruthenium complexes. The best match in harmonic vibrational frequencies between the experimental and calculated values has been reached at C = 0.15 for all the complexes. The absorption profile of the Fe(II) complex with the alternatively bonded CNS ligands strongly depends on the angle between them. The light-harvesting efficiency of the Fe(II) complexes is very similar (∼0.4) and sufficiently close to that of the Ru(II) complexes. The iron-based coordination compounds are considered as a prospective dye for dye-sensitized solar cells. The results of calculations were completed with experimental reference data, thus providing a systematic compendium for practical use.