For V [TCNE] y (solvent)(TCNE= tetracyanoethylene), the first room‐temperature molecular magnet, ... more For V [TCNE] y (solvent)(TCNE= tetracyanoethylene), the first room‐temperature molecular magnet, the mechanism for the strong exchange coupling in the family M [TCNE] y (solvent) has remained an open question. In an attempt to understand the magnetic ordering in ...
Hybrid organic/inorganic nanocomposite magnets are novel materials in which electrons in molecula... more Hybrid organic/inorganic nanocomposite magnets are novel materials in which electrons in molecular orbitals, consisting of superpositions of p and even s atomic orbitals, play a crucial role in the magnetic ordering. The interest in molecular magnets is twofold. The flexibility in synthesis brings the possibility of creating new materials that are experimental realizations for 'exotic' theoretical models. It is, therefore,
We report on the use of natural dyes, betalains, as pigments for Dye-Sensitized Solar Cells (DSSC... more We report on the use of natural dyes, betalains, as pigments for Dye-Sensitized Solar Cells (DSSC). Time-Dependent Density Functional Theory calculations provide the electronic spectra of the various types of betalain dyes and allow a discussion of their matching to the solar spectrum. Experimentally, we vary parameters such as the nature of the extracting solvent, the pH and the composition of the extract, to optimize the fabrication of DSSCs using betalains. Based on UV-Vis spectra correlated with electro-optic measurements providing the photovolatic conversion efficiency under standard AM1.5 conditions we find that the decrease of the pH of the dye solution leads to an increase of the DSSC performance, likely due to the increasing ratios of betacyanins with respect to betaxanthins in the extracts as well as the possible hydrolysis of betanin to betanidin. In order to fabricate better DSSCs using betalain natural dyes, we propose to use water as extracting solvent, to increase the...
ABSTRACT Harvesting energy directly from sunlight using photovoltaic technology is an essential c... more ABSTRACT Harvesting energy directly from sunlight using photovoltaic technology is an essential component of the future global energy production programs [1]. Photovoltaic devices, or solar cells, are based on the photoelectric effect, in which the incoming solar photons are absorbed in a sensitized semiconductor material freeing electric charges that are used to energize an external circuit [2]. The solar cells on the bases of nanocrystalline TiO(2) are usually sensitized by metal-organic dyes such as Ru-complexes with phenylpyridine and bipyridine ligands. The incident photon to current conversion efficiency (IPCCE) in the wavelength region 400-600 nm can be rather high [1, 2]. In order to improve the IPCCE value the heavier metal ions could be tested. Such sensitizers as coumarin, porphyrins, chlorophyll derivatives, antenna-sentsitizer polynuclear complexes and eosin have been studied and reported to be less efficient than the most effective Ru-based sensitizing dyes, called the black dye (BD) and N3 dye [2-4], used for the nanocrystalline TiO(2) solar cell. In this paper we are planning to understand the IPCE of a new dye-sensitizer in order to predict the higher absorption efficiency to solar spectrum and higher electron transfer rate from redox systems to oxidized dye. Some simple Ru(II)(bpy)(2)(CN)(2) complex is studied by DFT method with optimized structure and vibrational analysis in order to predict the role of vibronic perturbations in spectra and interface electron transfer rate.
We report on dye sensitized solar cells with PEDOT-PSS coated directly on flexible polyester subs... more We report on dye sensitized solar cells with PEDOT-PSS coated directly on flexible polyester substrate as counter electrode. The behavior of such plastic counter electrode in the presence of I - /I3 redox electrolyte has been investigated with X-ray photoelectron spectroscopy. We have found that some of iodine species are "trapped" within the PEDOT-PSS layer. The presence of I3 -
The molecular structure and the electronic densities of neutral and anionic hexacyanobutadiene (H... more The molecular structure and the electronic densities of neutral and anionic hexacyanobutadiene (HCBD), trans-C4(CN)6, as well as the electron affinity (EA) of HCBD have been studied using density functional theory (DFT) and perturbation theory (MP2) procedures. The optimized geometries showed that the HCBD molecule is not planar, with a 140° torsion angle about the central C–C bond. While the optimized
We report the first band structure calculations of the quasi-one-dimensional [MnTPP][TCNE] compou... more We report the first band structure calculations of the quasi-one-dimensional [MnTPP][TCNE] compounds (TPP = meso-tetraphenylporphyrinato, TCNE = tetracyanoethylene), based on Density Functional Theory (DFT) methods, in order to interpret the magnetic ordering in these prototypic systems. We compare and contrast the results of broken-symmetry DFT calculations for extended systems, with periodic boundary conditions, and for finite systems, magnetic dimers modeling the actual molecular magnets.
Quantum-chemical method of the density functional theory was employed to calculate, with the use ... more Quantum-chemical method of the density functional theory was employed to calculate, with the use of a B3LYP hybrid exchange-correlation functional, the IR absorption and Raman spectra of [Ru(bpy)2(CN)2] and [Ir(bpy)2(CN)2]+ complexes. All the normal vibrational frequencies were analyzed and new assignments of a number of bands in the IR absorption and Raman spectra were made. The role of vibrational motions
We report results of combined experimental and theoretical studies of dye‐sensitized solar cells ... more We report results of combined experimental and theoretical studies of dye‐sensitized solar cells (DSSCs) using 5‐(4‐sulfophenylazo)salicylic acid disodium salt, known as Mordant Yellow 10 (MY‐10), as TiO2 sensitizer. We focus on a single dye but vary the solvent and the pH of the solution as well as the photoelectrode preparation conditions to determine the conditions for best photovoltaic conversion efficiency. We found experimentally that the efficiency, measured under standard air mass 1.5 global (AM 1.5G) conditions, was higher in solutions of ethanol than of water, but still small (up to 0.174%), although the fill factor (FF) was large (up to 0.73). Of the dyes in ethanol, MY‐10 in alkaline solution showed the best matching of the solar spectrum but displayed the lowest efficiency. Density functional theory (DFT) calculations provided the optimized geometry, electronic structure, and electronic spectrum of the dye in fully protonated as well as partially and totally deprotonate...
In this work we perform a detailed analysis of the non-covalent effects that build the lattice of... more In this work we perform a detailed analysis of the non-covalent effects that build the lattice of the [Fe(bpca)2][Er(NO3)3(H2O)4]NO3 compound, made of cationic d units [Fe(bpca)2]+,(where Hbpca is bis(2-pyridilcarbonyl)amine), neutral f complexes [Er(NO3)3(H2O)4], and the NO3- counter-ion. All these units are interlinked by hydrogen bonds, their assembling benefiting also from electrostatic effects. A particularly interesting sub-ensemble of the crystal is the linear chain formed by the lanthanide units. Going beyond the usual qualitative description of the supramolecular assembling, we performed electron structure calculations on appropriate models related to the experimental structures. The formation energies of d and f coordination bonds are estimated in semi-quantitative manner, being compared with the intermolecular ones, due to hydrogen bonding and dipolar interactions.
A detailed study of the magnetic behavior of the molecule-based magnet, [MnOEP][HCBD], (OEP=meso-... more A detailed study of the magnetic behavior of the molecule-based magnet, [MnOEP][HCBD], (OEP=meso-octaethylporphyrinato, HCBD=hexacyanobutadiene) from 1.7 to 20 K was performed. The earlier reported magnetic transition at 19.6 K, ascribed to a crossover from a one-dimensional Heisenberg-like ferrimagnet to a two-dimensional Ising-like antiferromagnet, is further probed via ac-dc magnetic studies consisting of dc magnetization as a function of field at various temperatures, and magnetization as a function of temperature with both field cooling and zero-field cooling. In addition, the ac susceptibility was measured as a function of temperature and applied dc field. The appearance of a nonzero out-of-phase component of the ac susceptibility in zero dc field at 8 K accompanied by a shoulder in the in-phase component indicates the presence of a magnetic transition near that temperature. Irreversibilities and a spontaneous moment observed below 4.2 K indicate an additional lower temperature transition. The ac and dc data allow a determination of the temperature-field phase boundaries around these transitions. Evidence of a tricritical point at 2 kOe and 19.6 K and a multicritical point at 9.5 kOe and 8 K is presented. The nature of the ordered states, along with the possible mechanisms responsible for the transitions, including dipole-dipole interactions, are analyzed.
Reentrance in the Mn(tetracyanoethylene) x ⋅y(CH 2 Cl 2 ) high-T c molecule-based ferrimagnet. Ch... more Reentrance in the Mn(tetracyanoethylene) x ⋅y(CH 2 Cl 2 ) high-T c molecule-based ferrimagnet. Charles M. Wynn and Mihai A. Gîrţu Department of Physics, The Ohio State University, Columbus, Ohio 43210-1106. Jie Zhang ...
Magnetic properties and critical behavior of Fe(tetracyanoethylene) 2 ⋅x(CH 2 Cl 2 ): A high-T c ... more Magnetic properties and critical behavior of Fe(tetracyanoethylene) 2 ⋅x(CH 2 Cl 2 ): A high-T c molecule-based magnet. Mihai A. Gîrţu * and Charles M. Wynn Department of Physics, The Ohio State University, Columbus, Ohio 43210-1106. ...
For V [TCNE] y (solvent)(TCNE= tetracyanoethylene), the first room‐temperature molecular magnet, ... more For V [TCNE] y (solvent)(TCNE= tetracyanoethylene), the first room‐temperature molecular magnet, the mechanism for the strong exchange coupling in the family M [TCNE] y (solvent) has remained an open question. In an attempt to understand the magnetic ordering in ...
Hybrid organic/inorganic nanocomposite magnets are novel materials in which electrons in molecula... more Hybrid organic/inorganic nanocomposite magnets are novel materials in which electrons in molecular orbitals, consisting of superpositions of p and even s atomic orbitals, play a crucial role in the magnetic ordering. The interest in molecular magnets is twofold. The flexibility in synthesis brings the possibility of creating new materials that are experimental realizations for 'exotic' theoretical models. It is, therefore,
We report on the use of natural dyes, betalains, as pigments for Dye-Sensitized Solar Cells (DSSC... more We report on the use of natural dyes, betalains, as pigments for Dye-Sensitized Solar Cells (DSSC). Time-Dependent Density Functional Theory calculations provide the electronic spectra of the various types of betalain dyes and allow a discussion of their matching to the solar spectrum. Experimentally, we vary parameters such as the nature of the extracting solvent, the pH and the composition of the extract, to optimize the fabrication of DSSCs using betalains. Based on UV-Vis spectra correlated with electro-optic measurements providing the photovolatic conversion efficiency under standard AM1.5 conditions we find that the decrease of the pH of the dye solution leads to an increase of the DSSC performance, likely due to the increasing ratios of betacyanins with respect to betaxanthins in the extracts as well as the possible hydrolysis of betanin to betanidin. In order to fabricate better DSSCs using betalain natural dyes, we propose to use water as extracting solvent, to increase the...
ABSTRACT Harvesting energy directly from sunlight using photovoltaic technology is an essential c... more ABSTRACT Harvesting energy directly from sunlight using photovoltaic technology is an essential component of the future global energy production programs [1]. Photovoltaic devices, or solar cells, are based on the photoelectric effect, in which the incoming solar photons are absorbed in a sensitized semiconductor material freeing electric charges that are used to energize an external circuit [2]. The solar cells on the bases of nanocrystalline TiO(2) are usually sensitized by metal-organic dyes such as Ru-complexes with phenylpyridine and bipyridine ligands. The incident photon to current conversion efficiency (IPCCE) in the wavelength region 400-600 nm can be rather high [1, 2]. In order to improve the IPCCE value the heavier metal ions could be tested. Such sensitizers as coumarin, porphyrins, chlorophyll derivatives, antenna-sentsitizer polynuclear complexes and eosin have been studied and reported to be less efficient than the most effective Ru-based sensitizing dyes, called the black dye (BD) and N3 dye [2-4], used for the nanocrystalline TiO(2) solar cell. In this paper we are planning to understand the IPCE of a new dye-sensitizer in order to predict the higher absorption efficiency to solar spectrum and higher electron transfer rate from redox systems to oxidized dye. Some simple Ru(II)(bpy)(2)(CN)(2) complex is studied by DFT method with optimized structure and vibrational analysis in order to predict the role of vibronic perturbations in spectra and interface electron transfer rate.
We report on dye sensitized solar cells with PEDOT-PSS coated directly on flexible polyester subs... more We report on dye sensitized solar cells with PEDOT-PSS coated directly on flexible polyester substrate as counter electrode. The behavior of such plastic counter electrode in the presence of I - /I3 redox electrolyte has been investigated with X-ray photoelectron spectroscopy. We have found that some of iodine species are "trapped" within the PEDOT-PSS layer. The presence of I3 -
The molecular structure and the electronic densities of neutral and anionic hexacyanobutadiene (H... more The molecular structure and the electronic densities of neutral and anionic hexacyanobutadiene (HCBD), trans-C4(CN)6, as well as the electron affinity (EA) of HCBD have been studied using density functional theory (DFT) and perturbation theory (MP2) procedures. The optimized geometries showed that the HCBD molecule is not planar, with a 140° torsion angle about the central C–C bond. While the optimized
We report the first band structure calculations of the quasi-one-dimensional [MnTPP][TCNE] compou... more We report the first band structure calculations of the quasi-one-dimensional [MnTPP][TCNE] compounds (TPP = meso-tetraphenylporphyrinato, TCNE = tetracyanoethylene), based on Density Functional Theory (DFT) methods, in order to interpret the magnetic ordering in these prototypic systems. We compare and contrast the results of broken-symmetry DFT calculations for extended systems, with periodic boundary conditions, and for finite systems, magnetic dimers modeling the actual molecular magnets.
Quantum-chemical method of the density functional theory was employed to calculate, with the use ... more Quantum-chemical method of the density functional theory was employed to calculate, with the use of a B3LYP hybrid exchange-correlation functional, the IR absorption and Raman spectra of [Ru(bpy)2(CN)2] and [Ir(bpy)2(CN)2]+ complexes. All the normal vibrational frequencies were analyzed and new assignments of a number of bands in the IR absorption and Raman spectra were made. The role of vibrational motions
We report results of combined experimental and theoretical studies of dye‐sensitized solar cells ... more We report results of combined experimental and theoretical studies of dye‐sensitized solar cells (DSSCs) using 5‐(4‐sulfophenylazo)salicylic acid disodium salt, known as Mordant Yellow 10 (MY‐10), as TiO2 sensitizer. We focus on a single dye but vary the solvent and the pH of the solution as well as the photoelectrode preparation conditions to determine the conditions for best photovoltaic conversion efficiency. We found experimentally that the efficiency, measured under standard air mass 1.5 global (AM 1.5G) conditions, was higher in solutions of ethanol than of water, but still small (up to 0.174%), although the fill factor (FF) was large (up to 0.73). Of the dyes in ethanol, MY‐10 in alkaline solution showed the best matching of the solar spectrum but displayed the lowest efficiency. Density functional theory (DFT) calculations provided the optimized geometry, electronic structure, and electronic spectrum of the dye in fully protonated as well as partially and totally deprotonate...
In this work we perform a detailed analysis of the non-covalent effects that build the lattice of... more In this work we perform a detailed analysis of the non-covalent effects that build the lattice of the [Fe(bpca)2][Er(NO3)3(H2O)4]NO3 compound, made of cationic d units [Fe(bpca)2]+,(where Hbpca is bis(2-pyridilcarbonyl)amine), neutral f complexes [Er(NO3)3(H2O)4], and the NO3- counter-ion. All these units are interlinked by hydrogen bonds, their assembling benefiting also from electrostatic effects. A particularly interesting sub-ensemble of the crystal is the linear chain formed by the lanthanide units. Going beyond the usual qualitative description of the supramolecular assembling, we performed electron structure calculations on appropriate models related to the experimental structures. The formation energies of d and f coordination bonds are estimated in semi-quantitative manner, being compared with the intermolecular ones, due to hydrogen bonding and dipolar interactions.
A detailed study of the magnetic behavior of the molecule-based magnet, [MnOEP][HCBD], (OEP=meso-... more A detailed study of the magnetic behavior of the molecule-based magnet, [MnOEP][HCBD], (OEP=meso-octaethylporphyrinato, HCBD=hexacyanobutadiene) from 1.7 to 20 K was performed. The earlier reported magnetic transition at 19.6 K, ascribed to a crossover from a one-dimensional Heisenberg-like ferrimagnet to a two-dimensional Ising-like antiferromagnet, is further probed via ac-dc magnetic studies consisting of dc magnetization as a function of field at various temperatures, and magnetization as a function of temperature with both field cooling and zero-field cooling. In addition, the ac susceptibility was measured as a function of temperature and applied dc field. The appearance of a nonzero out-of-phase component of the ac susceptibility in zero dc field at 8 K accompanied by a shoulder in the in-phase component indicates the presence of a magnetic transition near that temperature. Irreversibilities and a spontaneous moment observed below 4.2 K indicate an additional lower temperature transition. The ac and dc data allow a determination of the temperature-field phase boundaries around these transitions. Evidence of a tricritical point at 2 kOe and 19.6 K and a multicritical point at 9.5 kOe and 8 K is presented. The nature of the ordered states, along with the possible mechanisms responsible for the transitions, including dipole-dipole interactions, are analyzed.
Reentrance in the Mn(tetracyanoethylene) x ⋅y(CH 2 Cl 2 ) high-T c molecule-based ferrimagnet. Ch... more Reentrance in the Mn(tetracyanoethylene) x ⋅y(CH 2 Cl 2 ) high-T c molecule-based ferrimagnet. Charles M. Wynn and Mihai A. Gîrţu Department of Physics, The Ohio State University, Columbus, Ohio 43210-1106. Jie Zhang ...
Magnetic properties and critical behavior of Fe(tetracyanoethylene) 2 ⋅x(CH 2 Cl 2 ): A high-T c ... more Magnetic properties and critical behavior of Fe(tetracyanoethylene) 2 ⋅x(CH 2 Cl 2 ): A high-T c molecule-based magnet. Mihai A. Gîrţu * and Charles M. Wynn Department of Physics, The Ohio State University, Columbus, Ohio 43210-1106. ...
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