Narrow Results

We carry out a computational investigation of the alkaline-earth (Ba)-based silicon and carbon oxide perovskites (BaSiO₃ and ${\text{BaCO}}_3)$ with the aim of their potential in wide-ranged applications. Exploiting the density functional theory (DFT) coded within Wien2K, we study the structural, electronic, and optical properties of these compounds. Modified Becke–Johnson (mBJ) potential, the established approach for obtaining accurate results, is employed to carry out the electronic investigation. With a simple cubic structure, we find that these materials exhibit metallic properties, as revealed by their mutually consistent band structure profiles and density of states. The valence band minima and conduction band maxima overlap at the $\mathrm{\Gamma }$ point in the band structure. We analyze the total and partial density of states to determine the proportional contributions of each atom, both in total and within individual subshells, such as the $p$- and $d$-subshells in the case of the partial density of states. In our investigation of the optical properties of these materials over the energy range of 0–14eV, we find that they effectively absorb ultraviolet and visible (UV–Vis) light. This shows that the studied compounds have potential applications in luminescence and devices requiring absorption in the UV range. BaCO₃ demonstrates more absorption spectra than the BaSiO₃ versus photon energy ranging from 1.7 to 3.1eV (visible range), suggesting that the BaCO₃ is more suitable than BaSiO₃ for applications that require UV absorption such as sunscreen, UV-blocking films, photodetectors and UV sensors and medical applications. We also find that BaCO₃ with a higher refractive index (11) compared to BaSiO₃ (4.2), is denser than BaSiO₃, resulting in a lower speed of light within the material. This suggests that BaCO₃ is more promising than BaSiO₃ for applications in eyewear. We infer that this study will guide and stimulate experimental investigations into these materials, given their potential for various applications.

Heme-type porphyrins can become distorted depending on their environment, altering their chemical and electronic properties. While trends have been established for several ruffle-distorted porphyrins, their research on synthetic models of heme-type porphyrins is limited. We identified a dynamic process on the ruffled porphyrin bis(2-methylpyridinato)iron(III)-Protoporphyrin-IX (2) that does not exist in bis(pyridinato)iron(III)-Protoporphyrin-IX (1). We modeled these molecules as {OMP(2-CH₃Py)₂Fe}${}^{+}$ and {[OMP](Py)₂Fe}${}^{+}$ respectively. Geometry optimization using density functional theory (DFT) suggests the ruffled conformation of 2 (angle x̄ of $-29.7^{\circ }$) and the planar conformation of 1. The calculated electron affinity and ionization potential vary depending upon ruffling. The calculated 0.253 eV difference in electron affinity and the 0.223 eV in ionization potential indicate that the reduction of the planar structure has a higher energy requirement than the ruffled-distorted structure but has a lower energy requirement for its oxidation. We found that these energy differences are not solely attributed to the distortion of the macrocycle. The difference is linked to the interaction between the d${}_{\text{x}\text{y}}$ orbital and the HOMO-1 3a${}_{2\text{u}}$, allowed by symmetry when a porphyrin ring has a ruffled conformation stabilizing the frontier orbitals, thus making the oxidation process have a higher energy barrier. On the other hand, the reduction process is facilitated by the interaction of metal d_π orbitals with the porphyrin 4e. These highlight the distinct differences between the ruffled and the planar conformations.

The advancement of science and technology is essential for the progress of nanotechnology, which plays a pivotal role in the development of miniaturized and energy-efficient devices. This investigation delves into the As-doped structures within one-dimensional germanene nanoribbons. Utilizing Density Functional Theory (DFT) in conjunction with the Vienna Ab initio Simulation Package (VASP), the study explores the electro-optical properties of the material influenced by As doping, examining both the doping position and density’s effects. Results indicate As significantly alters the electro-optical characteristics, with the semiconductor structure transitioning to metals in top and valley configurations, while meta and para configurations retain semiconductor properties with an indirect band gap. Analysis of bond length, bond angle, magnetism, formation energy and charge density difference elucidates As’ impact on hexagonal structure stability and electromagnetism properties of the system. Furthermore, a comprehensive investigation of optical properties not only offers insights into material systems but also highlights potential applications in optical communications and sensing technologies.

In this paper, we investigated the structural, elastic, topological-electronic properties as well as optical properties of two half-Heusler (HH) heavy fermions-based compounds: HoPtBi and HoPdBi. We accomplished our calculations in the framework of density functional theory (DFT), based on the full potential linearized augmented plane wave (FP-LAPW). Both compounds are antiferromagnetic (AFM) type-II as reported by experimental data so we carried out our study in the AFM type-II configuration. Considering the spin-orbit coupling, we found that the hydrostatic pressure leads to a phase transition from the trivial semimetal to the topological semimetal (TSM) because of band inversion for HoPdBi with no apparent effect of hydrostatic pressure on the topological phase for HoPtBi. We also studied their optical properties, without and with hydrostatic pressure. The first peak in reflectivity, absorption, optical conductivity spectra and energy loss factor are strongly influenced by the hydrostatic pressure. Both compounds exhibit a considerable first absorption peak in the visible and ultraviolet ranges and they are best candidates for solar cells considered essential in renewable energy.

The development of theoretical models that describe the electronic structures of the porphyrins and phthalocyanines using ZINDO and DFT techniques is rapidly approaching the point where the major spectral bands over a wide energy range, for both symmetric and non–symmetric molecules can be fully accounted for. However, although there has been much recent progress, theoretical models should always be tested accuracy by reference to the most recent electronic absorption and magnetic circular dichroism spectra available. This must be carried out by calculating absorption spectra to determine whether the major spectral features determined are accurately described. Spectroscopists need to provide fully analyzed data for this purpose as well as data recorded at low temperatures to enhance resolution. Since the porphyrin and phthalocyanine rings readily undergo oxidation and reduction, and well-characterized spectral data are available for many different redox states, new theoretical studies should also include the bands observed in the anion and cation radical species, as well as those of the neutral complex. This symposium addresses these goals by bringing together theoreticians and experimentalists to discuss their results.

The non-bonded interactions between a porphyrin molecule and a C₆₀ molecule, in the gas-phase, has been systematically investigated using various theoretical models. These are: (1) wavefunction-based methods, Hartree-Fock SCF (HF), second-order Møller-Plesset (MP2) theory, and the localized MP2 (LMP2) theory using the diatomics in molecules (DIM-LMP2) and triatomics in molecules (TRIM-LMP2) methods; (2) density functional theory (DFT), using non-local (BLYP, PW91), hybrid (B3LYP), and local (SVWN) functionals. Of the HF and DFT methods examined, corrected for BSSE using the counterpoise (CP) method, only the SVWN method predicts a close separation (2.5 Å) between the porphyrin and the C₆₀ molecules, in line with close contacts observed in crystal structures of cocrystallates of porphyrins and fullerenes (2.7-3.0 Å). The MP2 and LMP2 methods also predict a close contact between the two molecules although the MP2 and TRIM-LMP2 methods overestimate the interaction giving a separation < 2.5 Å while the DIM-LMP2 method gives a satisfactory separation of 2.9 Å. The SVWN and DIM-LMP2 methods also predict a reasonable complexation energy of ca. −13 kcal/mol (SVWN and DIM-LMP2 CP-uncorrected) and −7.9 kcal/mol (SVWN CP-corrected), whereas the MP2 and TRIM-LMP2 methods probably strongly overestimate the complexation energy. The remaining methods underestimate the complexation energy. The CP-uncorrected DIM-LMP2/6-31G(d) method gave the best estimate of the porphyrin-C₆₀ separation (2.9 Å) with a complexation energy of −13.3 kcal/mol; however, the more cost-effective SVWN functional gives satisfactory values for these quantities with the SVWN/6-311+G(d) level providing the best estimate for the complexation energy (−16.5 kcal/mol). The porphyrin-C₆₀ interaction was investigated in the giant triad 1 in which a zinc porphyrin, a dimethoxynaphthalene and a C₆₀ fullerene are separated by two norbornylogous bridge sections of six and five bond lengths, respectively. All methods predict the existence of a compact form of the molecule in which the porphyrin and C₆₀ moieties are only 2.9-4.3 Å apart (contact distance). This finding is consistent with certain photophysical properties of 1.

The synthesis of a new self-assembled porphyrin macrostructure based on disulfide bonds, is presented. This constitutes a new way to directly connect porphyrins in macromolecular arrays, to complement the usual methods of intermolecular hydrogen bonds and metal coordination bonding.

Catalases employ a tyrosinate-ligated ferric heme in order to catalyze the dismutation of hydrogen peroxide to O₂ and water. In the first half of the catalytic cycle, H₂O₂ oxidizes Fe(III) to the formally Fe(V) state commonly referred to as Compound I. The second half of the cycle entails oxidation of a second hydrogen peroxide molecule by Compound I to dioxygen. The present study employs density functional (DFT) calculations to examine the nature of this second step of the catalatic reaction. In order to account for the unusual choice of tyrosinate as an axial ligand in catalases, oxidation of hydrogen peroxide by an imidazole-ligated Compound I is also examined, bearing in mind that imidazole-ligated hemoproteins such as myoglobin or horseradish peroxidase tend to display little, if any, catalatic activity. Furthermore, in order to gauge the importance of the cation radical of Compound I in peroxide activation, the performance of Compound II (the one-electron reduced version of Compound I, formally Fe(IV)), is also examined. It is found that hydrogen peroxide oxidation occurs in a quasi-concerted manner, with two hydrogen-atom transfer reactions, and that the tyrosinate ligand is in no way required at this stage. We propose that the role of the tyrosinate is purely thermodynamic, in avoiding accumulation of the much less peroxide-reactive ferrous form in vivo – all in line with the predominantly thermodynamic role of the cysteinate ligands in enzymes such as cytochromes P450.

The Soret maxima of a number of metallotriarylcorroles shift sensitively in response to varying substituents on the meso-aryl groups. The effect is most pronounced for copper corroles but is not seen for silver and gold corroles. In the copper case, the effect has been attributed to a small HOMO–LUMO gap. Chromium-oxo corroles share a small HOMO–LUMO gap with copper corroles, as well as a substantially metal-based LUMO, yet the Soret maxima of chromium-oxo triarylcorroles do not shift in response to substitution on the meso-aryl groups. Molybdenum-oxo corroles are substituent-insensitive in the same sense. TDDFT calculations, focusing on chromium-oxo and molybednum-oxo triarylcorroles, are reported here in an attempt to explain the divergent spectroscopic behavior of different metallocorrole families.

Bis(tert-butyl isocyanide) iron(II) phthalocyanine complex in the crystalline form was obtained by a direct reaction of β-FePc with tert-butyl isocyanide. This complex crystallizes in the centrosymmetric space group P 2₁/c of the monoclinic system. The Fe(II) cation is equatorially ligated by the four N-isoindole atoms of Pc^2- macrocycle and axially by the C atom of tert-butyl isocyanide on both sides of a planar FePc molecule. Gas-phase conformation of the bis(tert-butyl isocyanide) iron(II) phthalocyanine molecule obtained by molecular orbital calculations shows a similar conformation as in the crystal. In both phases (solid and gas) a similar correlation between the equatorial Fe–N and axial Fe–C bonds are observed. Steric hindrance of the tert-butyl isocyanide molecules ligated to Fe in axial positions of planar FePc leads to the lowering of the π–π interaction between the π-clouds of Pc macrorings and makes the crystals of the bis(tert-butyl isocyanide) iron(II) phthalocyanine complex better soluble in the most organic solvents than the parent FePc compound. EPR and magnetic susceptibility measurements clearly show that ligation of the intermediate spin FePc by tert-butyl isocyanide leads to the change of the ground state from S = 1 (for FePc, e_g³b_2g²a_1g¹) to S = 0 yielding the low-spin complex ((CH₃)₃C-N≡C)₂FePc, e_g⁴b_2g²). The calculated three-dimensional MESP maps are helpful for understanding of the interaction between the FePc and tert-butyl isocyanide molecules forming bis(tert-butyl isocyanide) iron(II) phthalocyanine complex.

We have applied the density functional theory (DFT) to find stable dimeric structures on the potential energy surfaces (PESs) of slippage, tilting and rotation of the macrocycles of monohydroxy magnesium phthalocyanine complex. Gradual changing of a distance between Mg²⁺ ions and oxygen atoms of the OH-groups, as well as the dihedral angles between the planes passing through the isoindoline nitrogen atoms of different macrocycles has allowed finding of six stable dimeric structures that differ from each other by the spatial arrangement of the macrocycles. The most stable structure was found for the dimer in which two equivalent low-symmetry phthalocyanine macrocycles are double fixed by the coordination bonds between the complexing metal ions and oxygen of the OH-groups. This result is in agreement with our earlier experimental data.

The (nitro)($N$,$N^{\prime }$-dimethyl-4-aminopyridine) complex of perfluorinated cobalt(III) phthalocyanine Co(III)F₁₆Pc(Me₂Npy)(NO${}_2)$ catalyzes the electrochemical oxygen reduction reaction (ORR) in pH 4.0, 7.0, and 10.0 buffer and 0.05 M sulfuric acid solution when deposited on a glassy carbon electrode. Cyclic voltammetry (CV), rotating disk electrode voltammetry (RDE), and rotating ring-disk electrode voltammetry (RRDE) have been used to determine the reduction product as hydrogen peroxide although in concentrations too small to observe by qualitative methods such as oxidation of NaI in solution. The dependence of the values of the peak potentials for the reduction on the pH of the solution and the -log[Me₂Npy] are consistent with protonation up to pH 7.6 and pyridine ligand loss during the reduction. The addition of nitrite at 0.1 and 1 M to pH 7.0 solutions in contact with films of CoF₁₆Pc on the glassy carbon electrode decreases the ORR current and shifts the peak potential of the ORR from -0.21 V vs. NHE to -0.19 V vs. NHE. The addition of nitrite at 0.1 and 1 M to films of Co(III)F₁₆Pc(Me₂Npy)(NO${}_2)$ on glassy carbon, however, has no effect on either the current or the potential. While the electrochemical evidence for this proposal is not definitive, modeling has been used to examine the center of reduction in the alternative mechanisms by evaluation of the LUMOs of the hypothetical intermediates in both closed and open shell cases. The formation of five-coordinate Co(II)F₁₆Pc(NO) is proposed to occur initially in the reduction mechanism. It is also possible that O₂ reduction takes place at the NO ligand center by way of a nitrogen-bound peroxynitrite intermediate. The $\text{NO/NO}{}_2{}^{\mathrm{-}}$ ligand appears to remain bound during the ORR. Direct coordination of O₂ to the metal center requiring a six-coordinate species, Co(III)F₁₆Pc(O${}_2)$(NO${}_2)$, Co(II)F₁₆Pc(O${}_2)$(NO) or [Co(II)F₁₆Pc(O${}_2)$(NO${}_2)$]${}^{-}$ and has been considered in DFT modeling studies. The instability of the two-electron reduced, protonation species, [Co(I)F₁₆Pc(NO₂OH)]${}^{-}$ in its loss of peroxynitrous acid suggests that the reduction of O₂ may occur by two one-electron reduction steps rather than a two-electron step.

Porphyrin macrocycles play an important role in designing of fluorophores with superior light harvesting properties similar to that of antennas in biological systems. In this paper, new Zn(II)porphyrin dyes were investigated to improve the performance of the YD2-o-C8 using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations. Effects of various substituted and anchoring groups on basic porphine and Zn(II)porphyrin derivatives were systematically studied at the B3LYP/LanL2DZ level. The absorption spectra of Zn(II)porphyrin derivatives bearing one, two and four anchoring groups in the meso-positions were also studied. The calculations showed that a molecule [5, 10, 15, 20-(4-carboxyphenylethynyl)porphyrinato]Zn(II) have large absorption cross-section than available in the existing porphyrin dyes. The results of these calculations would open up enormous possibilities to develop porphyrin dyes characterized by high absorption cross-section for various light harvesting applications.

In this contribution, different porphyrin derivatives were experimentally synthesized and theoretically analyzed using several electronic structure methods to study the geometrical and electronic properties of A₄, trans-A₂B${}_2$and A₃B porphyrins bearing several functional groups (–OH, –COOH, -3,5-di-$t$Bu, –OCH₂CH₂CH₂COOEt and –OMe) suitable to be employed as dyes in Dye Sensitized Solar Cells (DSSC). A₄ (R $=$ -H, -OMe, -OH, -3,5-di-tert-butyl, –OCH₂CH₂CH₂COOEt) and A₃B (R${}_1=$R${}_2=$R${}_3=$–H; R${}_4=$–OH and R${}_4=$-3,5-di-$t$Bu) porphyrins were synthesized and characterized by UV-vis and ¹H NMR spectroscopies for comparison. The geometrical parameters were analyzed in the ground state and gas phase using the semiempirical method PM6 and the DFT functionals M06-2X and B3LYP, in combination with the 6-31G(d), DZVP and TZVP basis set. For calculations of the electronic and excited state properties, CAM-B3LYP, M06-2X and HSE06, using SMD as solvation model, were applied. This study revealed that HSE06/DZVP protocol is the best methodology to simulate electronic spectra in these porphyrin derivatives. Indeed, whereas substituent groups did not significantly affect the geometrical structure of the porphyrin derivatives studied, they do influence their electronic structures, mainly in the LUMO (lowest unoccupied molecular orbital) energy levels.

A novel clamshell-type binuclear zinc(II) phthalocyanine (2) was synthesized by cross condensation of the bisphthalonitrile (1) with 4-tert-butylphthalonitrile and zinc acetate in 1:10:4 ratio. The structure of the novel compound was characterized by elemental analysis, UV-vis, FT-IR (ATR), HR MALDI-TOF mass, ${}^{\mathrm{\text{1}}}$H NMR, ${}^{\mathrm{\text{13}}}$C DEPT NMR and ${}^{\mathrm{\text{1}}}$H–${}^{\mathrm{\text{1}}}$H COSY NMR methods. Applying electronic absorption spectroscopy and density functional theory (DFT) revealed that in THF the geometry of 2 is twisted to adopt an intermediate clamshell conformation in which the spacing between the Zn centers is about 8.1Å, providing a very good account of the observed spectrum exhibiting the characteristic B (Soret) band at 347 nm and the Q band at 673 nm. In solution, 2 was found to exist in non-aggregated form. The calculated fluorescence quantum yields (${\mathrm{\Phi }}_{\mathrm{\text{F}}}=$ 0.23 in THF and 0.10 in DMF) were relatively reduced in comparison to that of std ZnPc. In particular, understanding of leakage current conduction mechanisms in gate dielectrics is crucial for the development of field effect transistors with improved device performance. Analysis of the reverse bias current–voltage data indicated that the origin of leakage current conduction mechanisms in clamshell-type zinc(II) phthalocyanine is Poole-Frenkel emission. The capacitance density of 12.7 nF cm${}^{\mathrm{\text{-2}}}$ at 5 Hz. and 12.1 nF cm${}^{\mathrm{\text{-2}}}$ at 13 MHz was obtained with the FTO/Pc/Au sandwich structure.

This work describes the synthesis, spectral, aggregation and fluorescence properties of bis 4-[(4-tert-butylbenzyl)oxy substituted metal free (2), magnesium (3), zinc (4) and nickel (5) phthalocyanines. The syntheses of the novel compounds were confirmed by FT-IR, UV-vis, mass and NMR spectroscopy techniques, as well as elemental analysis. The effects of the nature of the central metal on the photophysical parameters of the phthalocyanine complexes are reported in this study. The photochemical properties (singlet oxygen quantum yields and photodegradation quantum yields) and photophysical properties (fluorescence behavior and fluorescence quantum yield) of the complexes were reported in different solutions (dimethyl sulfoxide (DMSO) and dimethyl formamide (DMF) and tetrahydrofuran (THF)). However, energy minimized structure, vibrational frequency, molecular orbital levels and electronic absorption spectra were obtained by DFT calculations which supported the experimental results.

The Density Functional Theory (DFT) method was employed to study the properties of the C${}_{\mathrm{\text{20}}}$ complex with tetraphenylporphyrin (TPP). Calculations were performed in vacuum and in the presence of different solvents. Strong interaction between the C${}_{\mathrm{\text{20}}}$ cluster and TPP molecule was observed. To understand the effect of C${}_{\mathrm{\text{20}}}$ on electrochemical properties of TPP, electron transfers from and toward the porphyrin and C${}_{\mathrm{\text{20}}}$-TPP complex were studied. It was shown that the presence of C${}_{\mathrm{\text{20}}}$ influences the electron transfer reaction toward the porphyrin molecule and causes transfer of one and two electrons to C${}_{\mathrm{\text{20}}}$-porphyrin, which is more favorable compared with porphyrin alone. However, C${}_{\mathrm{\text{20}}}$ has slight effect on electron transfer from porphyrin and on positive ion formation. The effect of solvent type on electron transfer energy was studied for these reactions, and it was shown that solvents with higher permittivity have lower electron transfer reaction energy, which may be predicted from ionic character of the products.

Three water-soluble quaternized metal-free tetra-(3-pyridyl)bacteriochlorins were synthesized and characterized by UV-vis, MCD, and NMR spectroscopy as well as elemental analysis. DFT calculations are indicative of the $\mathrm{\Delta }$HOMO $<$$\mathrm{\Delta }$LUMO relationship, which correlates well with the experimentally observed by MCD spectroscopy for all bacteriochlorins “reversed” sign sequence in the Vis-NIR region. TDDFT calculations also correctly predict large splitting between the $Q_x$ and $Q_y$ bands as well as splitting of the Soret band observed experimentally in all bacteriochlorins.

Visible and infrared spectroelectrochemistry of Fe(OEPone)(NO) (H₂OEPone = octaethylporphinone) were examined in methylene chloride and THF. The visible spectra of Fe(OEPone)(NO) were similar in both solvents. Unlike other ferrous porphyrin nitrosyls, a six-coordinate complex was formed with THF as a ligand. This led to two nitrosyl bands in the infrared spectrum. The absorbance of these bands depended on the concentration of THF in the solution. Solvation and coordination effects on the carbonyl and nitrosyl bands were observed for both the nitrosyl and reduced-nitrosyl complexes. DFT calculations were carried out to interpret the spectral changes.

Marquette University, Raynor Memorial Libraries, Chemistry Research Data: https://epublications.marquette.edu/chem_data/1/

The syntheses of indium, gallium and aluminum porphyrin dimers with a single hydroxo-bridge, $\{$[M(Porph)]₂(OH)${\}}^{+}$, are described. Emphasis is given to indium and gallium derivatives. The X-ray structures for $\{$ [Ga(OEP)]₂(OH)$\}$ ClO₄ and $\{$ [In(OEP)]₂(OH)$\}$ ClO₄ (two forms) are presented. The dimeric molecules can be synthesized by the acid-treatment of the corresponding hydroxo-ligated monomeric complexes [M(OEP)(OH)] and [M(TPP)(OH)]. The nature of the starting material (the hydroxo-ligated monomer) was first suggested by IR spectroscopy and further proved by proton-deuterium exchange followed by ¹H NMR spectroscopy. The structure of a monomeric indium hydroxide complex, [In(OEP)(OH)], is also presented. The synthesis of the dimer for all metals can be monitored by UV-vis spectroscopy, which clearly demonstrates that a blue-shift of the Soret band accompanies formation of the dimer from the monomer. A strong $\pi$–$\pi$interaction between the two porphyrin rings of these $\mu$-hydroxo-bridged dimers is confirmed both by solution state studies (¹H NMR and UV-vis spectroscopy) and the X-ray structures of $\{$ [M(OEP)]₂(OH)$\}$ ClO₄ (M = In, Ga). In addition, exposure of methylene chloride solutions of these bridged complexes to white light afforded the corresponding chloro derivatives, [M(Porph)Cl]. The stereochemistry of a range of $\mu$-hydroxo dimers is discussed and DFT simulations at the HSEH1PBE/SDD level of theory provide suitable structural models and further electronic structure insights on selected [Ga(Porph)(OH)] and $\{$ [Ga(Porph)]₂(OH)$\}$${}^{+}$ derivatives.