Time-dependent Density Functional Theory Analysis Research Articles

Intramolecular Charge Transfer and Stimuli-Responsive Emission in Cholesterol-Appended Phenothiazine-Cyanostyryl-Based Donor-Acceptor Systems.

Organic fluorescent molecules have received considerable attention owing to their various optoelectronic applications. Herein, we report the design and synthesis of two cholesterol-functionalized cyanostyrene-phenothiazine-based D-π-A systems that are emissive in both the solution and solid states. The newly synthesized cholesterol-appended phenothiazine-cyanostyrene diads PTCS-1 and PTCS-2 vary in the N-alkylation of phenothiazine, respectively, with─octyl and─hexyl chains. Both molecules are highly fluorescent and show reasonably good quantum yields in nonpolar solvents because of twisted intramolecular charge transfer (TICT). The molecules exhibit aggregation-induced emission in the solid state. Due to the presence of flexible alkyl chains in the phenothiazine and cholesterol moieties, PTCS-1 and PTCS-2 show mechanochromic luminescence switching in response to external shear stress and emission recovery under methanol vapor. Powder X-ray diffraction studies prove that the emission switching on the applied stimuli in both PTCS-1 and PTCS-2 is attributed to the reversible transformation between the crystalline and amorphous states. Time-dependent density functional theory (TD-DFT) studies are carried out to gain insight into the ICT interactions. TD-DFT analysis at the TD-M06-2X/def2-TZVP level further revealed that in both molecules, the lowest unoccupied molecular orbital (LUMO) + 2, LUMO, highest occupied molecular orbital (HOMO), and HOMO - 1 orbitals are responsible for the charge transfer interactions. These ICT interactions are identified as π-π* type interactions.

Theoretical approach on Hg2+, Pb2+ and Cd2+ ions adsorption via phographene

Due to widespread concerns regarding health and environmental risks associated with heavy metal ions, wastewater must be cleaned of them. As part of this study, phographene (PG) is investigated for removing Pb2+, Hg2+, and Cd2 + ions from wastewater. It has been proven that PG can be effective in removing heavy metals from watery media. The present study utilizes density functional theory (DFT). By the absorption of Pb2+, Hg2+, and Cd2 + ions, the pure PG gap (HOMO-LUMO) is significantly narrowed. Research shows that faster electron transport rates result in larger charge transfers between cations and PGs and higher binding energies. In the studied complexes, time-dependent DFT analysis indicates a charge transfer between the ligand and the metal. Based on the theory analysis conducted in this paper, experimental studies can be conducted to find PG-based materials that effectively remove contaminants from wastewater.

Investigation of J-Aggregates of 2,3,7,8,12,13,17,18-Octabromo-5,10,15,20-tetrakis(4-sulfonatophenyl) Porphyrin in Aqueous Solutions.

The highly distorted water-soluble 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (Br8TPPS44-) is readily protonated under acidic pH, forming the diacid H2Br8TPPS42- and subsequently the zwitterionic H4Br8TPPS4, which eventually evolves into J-aggregates. These latter species exhibit a relevant bathochromic shift with respect to the monomer with a quite sharp band due to motional narrowing. The depolarization ratio measured in resonant light scattering spectra allows estimating a tilt angle of ~20° of the porphyrins in the J-aggregate. The kinetic parameters are obtained by applying a model based on the initial slow nucleation step, leading to a nucleus containing m monomers, followed by fast autocatalytic growth. The kc values for this latter step increase on decreasing the acid concentration and on increasing the porphyrin concentration, with a strong power-law dependence. No spontaneous symmetry breaking or transfer of chirality from chiral inducers is observed. Both Atomic Force Microscopy (AFM) and Dynamic Light Scattering (DLS) point to the presence, in both the solid and solution phases, of globular-shaped aggregates with sizes close to 130 nm. Density functional theory (DFT) calculations performed on simplified models show that (i) upon protonation, the saddled conformation of the porphyrin ring is slightly altered, and a further rotation of the aryl rings occurs, and (ii) the diacid species is more stable than the parent unprotonated porphyrin. Time-dependent DFT analysis allows comparing the UV/Vis spectra for the two species, showing a consistent red shift upon protonation, even if larger than the experimental one. The simulated Raman spectrum agrees with the experimental spectrum acquired on solid samples.

Structural, Spectroscopic, and Bonding Analyses of La(III)/Ce(III)-Tetrel Ate-Complexes.

In comparison with the research of transition-metal-tetrel complexes, the chemistry of lanthanide tetrel complexes, especially for these bearing heavier tetrel element ligands, is still relatively underexplored. In this research, K[Cp3Ln(III)CH2Ph], [(DME)3Li][Cp3Ln(III)GePh3], and [(DME)3Li][Cp3Ln(III)SnPh3] [Ln(III) = La(III), Ce(III)] have been synthesized by reacting [(DME)3Na][Cp3La(μ-Cl)LaCp3] or Cp3Ce(THF) with alkali metal alkyl, germyl, and stannyl reagents. Additionally, [(DME)3Li][Cp3Ce(III)SnPh3] is the first example of Ce(III)-Sn bond containing complex. All the obtained early Ln(III) tetrel ate-complexes were structurally analyzed by single-crystal X-ray diffraction. The formal shortness ratios of the Ln(III)-C, Ln(III)-Ge, and Ln(III)-Sn bonds are in the range of 1.03-1.11. Together with the previously reported [(DME)3Li][Cp3Ln(III)SiPh3], a group of tetrel (up to Sn) lanthanocene ate-complexes with an analogous coordination pattern are presented. Computational studies suggest the strongly polarized nature of the Ln(III)-E (E = C, Si, Ge, Sn) bonds in these complexes, with 77-85% atomic orbital contribution from tetrel elements and 15-23% atomic orbital contribution from Ln(III). The UV-vis measurements of this series of complexes show that the characteristic absorptions are hypsochromically shifted for Ln(III) heavier tetrel complexes in comparison to their lighter congeners. Moreover, the HOMOs, in which the Ln(III)-E σ-bonding orbitals are the dominant components, of these series complexes act as donor orbitals of the major electron transitions, as being disclosed by the time-dependent density functional theory analysis.

Synthesis, characterization and exploration of photovoltaic behavior of hydrazide based scaffolds: a concise experimental and DFT study.

Solar energy being a non-depleting energy resource, has attracted scientists' attention to develop efficient solar cells to meet energy demands. Herein, a series of hydrazinylthiazole-4-carbohydrazide organic photovoltaic compounds (BDTC1-BDTC7) with an A1-D1-A2-D2 framework was synthesized with 48-62% yields, and their spectroscopic characterization was accomplished using FT-IR, HRMS, 1H and 13C-NMR techniques. Density functional theory (DFT) and time dependent DFT analyses were performed utilizing the M06/6-31G(d,p) functional to calculate the photovoltaic and optoelectronic properties of BDTC1-BDTC7via numerous simulations of the frontier molecular orbitals (FMOs), transition density matrix (TDM), open circuit voltage (V oc) and density of states (DOS). Moreover, the conducted analysis on the FMOs revealed efficient transference of charge from the highest occupied to the lowest unoccupied molecular orbitals (HOMO → LUMO), further supported by TDM and DOS analyses. Furthermore, the values of binding energy (E b = 0.295 to 1.150 eV), as well as reorganization energy of the holes (-0.038-0.025 eV) and electrons (-0.023-0.00 eV), were found to be smaller for all the studied compounds, which suggests a higher exciton dissociation rate with greater hole mobility in BDTC1-BDTC7. V oc analysis was accomplished with respect to HOMOPBDB-T-LUMOACCEPTOR. Among all the synthesized molecules, BDTC7 was found to have a reduced band gap (3.583 eV), with a bathochromic shift and absorption maximum at 448.990 nm, and a promising V oc (1.97 V), thus it is regarded as a potential candidate for high performance photovoltaic applications.

Molecular characteristics of 1-benzhydrylazetidin-3-ol by time-dependent density functional theory analysis

1-benzhydrylazetidin-3-ol (BA3) molecule was characterized by its experimental UV–Visible (200–400 nm) spectrum in a solution of chloroform and simulated spectrum using time-dependent density functional theory (TD-DFT). The computations were made using density functional theory employing B3LYP exchange–correlation functional in conjunction with the 6–311++G(d,p) basis set. Good agreement was observed between measured and computed quantities corresponding to structure parameters and UV–Visible spectrum. The chemical reactivity of the molecule was identified with the help of frontier molecular orbital (FMO) parameters. The non-linear optical (NLO) behavior of the molecule was studied by computing the values of hyperpolarizability (βt), polarizability (αt), and dipole moment (μt). NBO analysis has been used to examine the molecule's stability as a result of hyper-conjugative interactions and charge delocalization. According to NBO analysis, the title molecule has O-H• • • N and C-H• • •N bifurcated hydrogen bonds, which is compatible with the result of the molecular structure study. It is evident from the computed HOMO and LUMO energies that charge transfer takes place within the molecule. The NLO parameters also confirm these findings. Thermodynamic parameters were also computed for this molecule.

The nonlinear optical properties of AlPc-Cl organic compound using DFT and TD-DFT analysis, as well as filter optical-electrical properties

The properties of nonlinear optical (NLO) are examined, and the results confirm the 2.19[Formula: see text]eV HOMO–LUMO mismatch. In the AlPc cluster, certain functional bond lengths and bond angles have been observed. Quantum chemical methods (density functional theory (DFT) and time-dependent density functional theory (TD-DFT)) and vibrational spectra properties of AlPc are studied. An X-ray pattern reveals the crystalline structure along the (242) orientation of AlPc organic thin layer. An ultraviolet-visible (UV–Vis) also shows the frequency selective behavior of the device. The absorbance of such layer exhibits a high value within UV range and two consecutive peaks within the visible range. Spin coating is used to make an organic diode based on the Aluminium phthalocyanine (AlPc-Cl) molecule. Under dark and light conditions, electrical characterization of Ag/AlPc/Si/Au is obtained. The diode’s high rectifying capability (about [Formula: see text] is subsequently discovered. While the height barrier is constant and saturation current is greatly reliant on light, the ideality factor of such a diode increases to 6.9 which confirms the nonideality of such a device. The Cheung–Cheung technique is employed to further the investigation and gain additional data such as series resistance and barrier height.

Nonadiabatic Exchange-Correlation Potential for Strongly Correlated Materials in the Weak and Strong Interaction Limits

In this work, nonadiabatic exchange-correlation (XC) potentials for time-dependent density-functional theory (TDDFT) for strongly correlated materials are derived in the limits of strong and weak correlations. After summarizing some essentials of the available dynamical mean-field theory (DMFT) XC potentials valid for these systems, we present details of the Sham–Schluter equation approach that we use to obtain, in principle, an exact XC potential from a many-body theory solution for the nonequilibrium electron self-energy. We derive the XC potentials for the one-band Hubbard model in the limits of weak and strong on-site Coulomb repulsion. To test the accuracy of the obtained potentials, we compare the TDDFT results obtained with these potentials with the corresponding nonequilibrium DMFT solution for the one-band Hubbard model and find that the agreement between the solutions is rather good. We also discuss possible directions to obtain a universal XC potential that would be appropriate for the case of intermediate interaction strengths, i.e., a nonadiabatic potential that can be used to perform TDDFT analysis of nonequilibrium phenomena, such as transport and other ultrafast properties of materials with any strength of electron correlation at any value in the applied perturbing field.

Diorganostannoxanes Stabilized by Intramolecular N→Sn Coordination Approach: Synthesis, Structure, TD-DFT and Hirshfeld Surface Analysis

A mononuclear diorganotin halide and two dinuclear diorganostannoxanes containing Sn-O unit were synthesized using intramolecular coordination approach involving 2-phenylazophenyl substituent on tin. [(R2Sn)2(μ2-O)Cl2]·CH2Cl2 (1) was obtained by partial hydrolysis of R2SnCl2 (R = 2-phenylazophenyl) using equimolar sodium hydroxide whereas, [R2Sn(cupf)Cl] {cupf= cupferronato} (2) was obtained by the room temperature reaction of cupferron with R2SnCl2. [(R2Sn)(μ2-OH)(OOCCH=CHC6H5)]2·2H2O (3) was obtained by the reaction of cinnamic acid and R2SnO (R = 2-phenylazophenyl) in refluxing toluene. The molecular structures of complex 1–3 were established using single crystal x-ray crystallography. Time dependent density functional theory (TD-DFT) calculations revealed that the transitions occurring in 1–3 are mainly ligand-to-ligand type. Intermolecular interactions in 1–3 were studied using Hirshfeld surfaces. 2D fingerprint plots illustrated that supramolecular assemblies of 1 and 2 were influenced majorly by CH…π, N…H, Cl…H and O…H interactions whereas supramolecular assembly of 3 mainly consisted of CH…π, N…H and O…H interactions.

Quantum chemical modeling, synthesis, spectroscopic (FT-IR, excited States, UV–Vis) studies, FMO, QTAIM, NBO and NLO analyses of two new azo derivatives

• Two new azo derivatives were synthesized and FT-IR, UV-Vis and NMR spectra were measured and compared with theoretical calculations. • Detailed structural, physical and chemical properties were studied. • Hyperpolarizability calculations reveal suitability for optoelectronic and photonic applications. In this research, we report the results of experimental and density functional theory (DFT)/time-dependent DFT analyses of two new azo derivatives that absorb light in the visible range: (E)-2-((4-(diethylamino)phenyl)diazenyl)-6-methoxy-3-methylbenzo[d]thiazol-3-ium ( I ) and N,N-diethyl-4-((6-methoxybenzo[d]thiazol-2-yl)diazenyl)aniline ( II ) in the presence of water ( I ) and chloroform ( II ). The molecular geometry and excited states of the compounds were investigated, and their natural bond orbital, frontier molecular orbital, quantum theory of atoms in molecules, and nonlinear optical (NLO) parameters were calculated. In addition, Fourier-transform infrared, nuclear magnetic resonance, and ultraviolet/visible spectral parameters were generated from the derived structures and compared to experimental spectral parameters. The practical applicability of the azo derivatives was investigated by determining their electronic and NLO properties, which demonstrated that both molecules have potential for optoelectronic and photonic applications. A high degree of approximation between the calculated and experimental results was demonstrated.

Effect of the mixture composition of C4mimBF4/acetonitrile on the charge transfer in Coumarin 153: DFT and TD-DFT analysis

In this work, we studied by means of density functional theory (DFT) and time-dependent DFT(TD-DFT) using the effect of the mixture composition C4mimBF4/acetonitrile on the charge transfer in Coumarin 153(C153) after photoexcitation. The mixture composition was characterize by their corresponding static dielectric constant εm. The PBE0 and M06-2X functionals combined with linear response (LR) and state specific (SS) solvation schemes were used to obtain various electronic properties of C153 in both ground and excited states. Our results show that the calculated fluorescence Stoke shift, using the state specific solvation scheme correlates well with the corresponding experimental data obtained for C153 dissolved in other solvents have the same static dielectric constant as of the C4mimBF4/acetonitrile mixture. The charge transfer was quantified using descriptors such as charge qCT, distance dCT, and the dipole moment μCT between the ground and the excited state. These descriptors were calculated based on four different partial atomic charge models, namely Mulliken, Natural Populations Analysis, Hirshfeld, and Merz–Kollman. The charge transfer also was quantified using descriptors based on the electrostatic surface potential namely the polarity index. Both PBE0 and M06-2X functionals combined with the Linear Response solvation scheme result in a systematic increase of the qCT, dCT, and μCT with increasing εm, while they decrease for most of the partial atomic charge models when the State Specific solvation scheme is used. This later result points out that this solvation scheme is not suitable for the description of the excited state of C153 in this mixture. Our results show that the extent of change of these descriptors is small and indicates that the effect of the mixture composition on the charge transfer in C153 is weak.

First-principles based theoretical investigation of impact of polyolefin structure on photooxidation behavior.

Despite their mass production and large applications, polyolefins' stability and durability toward the air, moisture, and weather resistance is a challenge for the ecosystem. After long-term exposure to ultraviolet (UV) radiation or high-temperature or erosion, polyolefins undergo degradation generating microplastics (MPs). The MPs generated after the degradation of these polyolefins are hazardous for the ecosystem. In the present work, we have carried out density functional theory (DFT) studies to investigate the photodegradation of six different polyolefins ranging from polyethylene to polydecene, differing in side-chain. Herein, we have investigated photooxidized derivatives of different polyolefins and analyzed their relative stability, conformations, UV-visible spectral behavior, and carbonyl index. The photooxidized derivatives of various polyolefins formed during degradation are examined. The time-dependent density functional theory analysis confirms that the carbonyl groups of photooxidized products show absorption peak in Infrared (IR) and visible region, acting as light-absorbing species. The relative stabilities of hydroperoxide formed during photo/thermal oxidation of different polyolefins have been evaluated to explain the degradation behavior. The oligomerization and stabilization energies of their corresponding hydroperoxide's were computed and analyzed to explain the degradation behavior of the polyolefins. The computed results suggest that polyolefins in their pristine state are stable toward photooxidation, but chemical impurities like carbonyl, unsaturated carbonyl, carboxylic acid, and hydroperoxide derivatives make them prone to undergo degradation, a fundamental process leading to generation of MPs. The comparative results confirmed that the side-chain length affects the stability and degradation of different polyolefins toward photooxidation.

Fulgide Derivative-Based Solid-State Reversible Fluorescent Switches for Advanced Optical Memory

Fulgide Derivative-Based Solid-State Reversible Fluorescent Switches for Advanced Optical Memory

Photoinduced Intermolecular Electron Transfer in Gas Phase Ion Pairs of the 1-Ethyl-3-methylimidazolium Cation and the Bis(trifluoromethylsulfonyl)imide Anion.

In this study, the UV photodissociation of gas phase ion pairs of the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [emim]+[tf2n]-, is shown to proceed primarily through radical intermediates. [emim]+[tf2n]- ion pairs have been shown previously to undergo two-photon-dependent dissociation, but the mechanisms of this have not been probed in detail. By employing a two-laser pump probe spectroscopy and time-dependent density functional theory (TD-DFT) calculations, we have illustrated that one of the major UV photodissociation pathways in [emim]+[tf2n]- ion pairs is an intermolecular electron transfer wherein the anion transfers an electron to the cation resulting in two neutral open-shelled products. These products were observable for at least 1.6 μs post photodissociation, the experimental limit, via detection of the [emim]+ cation. This data demonstrates that the likely photoproducts of [emim]+[tf2n]- UV photodissociation are two neutral species that separate spatially, demonstrated through lack of observed relaxation pathways such as electron recombination. TD-DFT and frontier molecular orbital analysis calculations at the MN15/6-311++G(d,p) level are employed to aid in identifying excited state characteristics and support the interpretations of the experimental data. The energetic onset of the intermolecular electron transfer is consistent with previously observed [emim]+[tf2n]- absorption spectra in the bulk and gas phases. The similarities between bulk and gas phase UV spectra imply that this electron-transfer pathway may be a major photodissociation channel in both phases.

TD-DFT Analysis of the Dissymmetry Factor in Camphor

The fact that the dissymmetry lgeb (g-factor) of camphor is large has been known for decades, and the interpretation of the observed data has also been known for a long time. However, due to the ability of quantum chemical methods to describe chiroptical phenomena more appropriately, additional approaches based on these methods have been successful employed. The g-factor lgebra in S-camphor and L-tryptophan have been investigated by UV-Vis and electronic circular dichroism (ECD) spectroscopies of the n ® p* electronic transition. Time-dependent density functional theory (TD-DFT) calculations at CAM-B3LYP/6-311++G(3df,2p)//B3LYP/6-311++G(2d,p) level of theory including Grimme’s dispersion effects have been performed. The lgebra effect was added using solvation model based on density (SMD) approach in solvation environment. The results permit insights into the ground and excited states electronic properties associated with the g-factor. The theoretical spectra showed good similarity with the experimental ones. The theoretical ECD of camphor was found at 282 nm, whereas the experimental shows its maximum at 290 nm. Regarding the maximum value of the molar absorptivity lgebrante, the theoretical and experimental values were 16.2 and 30.2 M-1 cm-1, respectively. The same concordance was obtained for g-factor, as follows: -0.0445 and -0.0886, for experimental and theoretical results, respectively.

Near-Infrared-Absorbing Indolizine-Porphyrin Push–Pull Dye for Dye-Sensitized Solar Cells

Porphyrins are attractive chromophores for application in dye-sensitized solar cells (DSCs), as judicious tuning of donor-acceptor properties can enable excellent near-infrared (NIR) absorption and exceptional device performance. Here, we report a porphyrin-based dye (SM85) conjugated to the planar strong electron donor, indolizine, designed to extend absorption further into the NIR region by inducing π-π interactions such as head-to-tail dye aggregation. The optoelectronic consequences of indolizine incorporation in SM85 include raising the ground-state oxidation potential and broadening and red-shifting ultraviolet-visible-NIR absorptions, along with increased molar absorptivity when compared to the dye SM315. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations confirm the push-pull character of SM85, which features an overlap of frontier occupied and unoccupied orbitals. Steady-state spectrophotometric analyses reveal the presence of solution aggregates via absorption and emission spectroscopies. Aggregate modes were probed by DFT and TD-DFT analyses, and plausible models are presented. SM85-based DSC devices demonstrate a 5.7% power conversion efficiency (PCE) at full sun (7.4% PCE at 10% sun) with an exceptional improvement to the incident photon-to-current conversion onset at ∼850 nm. Current dynamics measurements, time-correlated single photon counting, and computational analyses are used to better understand device performances. This study puts forward a novel intramolecular charge-transfer porphyrin system with a dramatic shift into the NIR region, as is needed for nonprecious metal-based sensitizers, and provides an example of controlled, donor-acceptor-mediated aggregation as a complementary strategy to traditional donor-acceptor modifications to single-molecule π-systems in accessing enhancements in long wavelength light harvesting in molecular-based optoelectronic devices.

Pyridine-2-carboxylato chelated acylrhodium(III) organometallics: Spectroscopic, structural and theoretical studies

The heterogeneous phase reaction of Rh(MeLsb)(PPh3)2Cl2 (1) with the sodium salt of three differently substituted picolinate ligands [Na(R-pic), R = H, Me, Cl] in dichloromethane–acetone–water medium afforded the complexes of the type Rh(Lal)(PPh3)2(R-pic) (2(R)) in excellent yield. These are the first examples of acylrhodium(III) complexes with the picolinate ligand. The chelation of the picolinate ligand is attended with the cleavage of the two RhCl bonds and concomitant hydrolysis of the aldiminium function in 1. The picolinate ligand is coordinated to the rhodium center as bidentate N,O-donor forming five-membered chelate ring. The spectral (UV–Vis, IR, NMR) and electrochemical data of the complexes are reported. The identity of 2(H) has been established by single-crystal X-ray structure determination which revealed distorted octahedral RhCNO2P2 coordination sphere. The pairs (P,P), (C,O) and (O,N) define the three trans directions. The electronic structures and the absorption spectra of the complexes are also scrutinized by the density functional theory (DFT) and time-dependent DFT analysis.

Structural investigation of a new cadmium coordination compound prepared by sonochemical process: Crystal structure, Hirshfeld surface, thermal, TD-DFT and NBO analyses

A new nanostructured cadmium complex containing a tridentate Schiff base ligand was sonochemically synthesized and characterized by XRPD, FT/IR, NMR, and single crystal X-ray crystallography. Structural data showed that cadmium(II) ion is surrounded by three nitrogen atoms of Schiff base ligand and two iodide anions. The crystal packing was contained the intermolecular interactions such as CH⋯O, CH⋯I and π⋯π interactions organizing the self-assembly process. Hirshfeld surfaces and corresponding fingerprint plots have been used for investigation of the nature and proportion of interactions in the crystal packing. FT/IR, NMR and XRD data were in agreement with the X-ray structure and confirm the phase purity of the prepared sample. The molecular structure of the complex was optimized by density functional theory (DFT) calculation at the B3LYP/LANL2DZ level of theory and the results were compared with experimental ones. For more concise study of structure and spectral aspects of the complex, natural bond orbital (NBO) analysis and time-dependent density functional theory (TD-DFT) have been also performed. Thermal stability of the cadmium iodide complex was investigated by thermogravimetric analysis (TGA). Finally, cadmium oxide nanoparticles was prepared by direct calcination of CdLI2 complex as a new precursor.

Time-Dependent Density Functional Theory Analysis of Triphenylamine-Functionalized Graphene Doped with Transition Metals for Photocatalytic Hydrogen Production.

The electronic structures and optical properties of triphenylamine-functionalized graphene (G-TPA) doped with transition metals, using water as a solvent, were theoretically investigated to verify the efficiency of photocatalytic hydrogen production with the use of transition metals. This study was performed by Density Functional Theory and Time-dependent Density Functional Theory through Gaussian 09W software, adopting the B3LYP functional for all structures. The 6-31g(d) basis set was used for H, C and N atoms, and the LANL2DZ basis set for transition metals using the Effective Core Potentials method. Two approaches were adopted: (1) using single metallic dopants (Ni, Pd, Fe, Os and Pt) and (2) using combinations of Ni with the other dopants (NiPd, NiPt, NiFe and NiOs). The DOS spectra reveal an increase of accessible states in the valence shell, in addition to a gap decrease for all dopants. This doping also increases the absorption in the visible region of solar radiation where sunlight is most intense (400 nm to 700 nm), with additional absorption peaks. The results lead us to propose the G-TPA structures doped with Ni, Pd, Pt, NiPt or NiPd to be novel catalysts for the conversion of solar energy for photocatalytic hydrogen production, since they improve the absorption of solar energy in the range of interest for solar radiation; and act as reaction centers, reducing the required overpotential for hydrogen production from water.

Mechanism and oxidation state involved in the nitric oxide (NO) photorelease in a terpyridine-bipyridine-based ruthenium nitrosyl complex

A new nitric oxide (NO) donor of formula [RuII(MeO-Phtpy)(bpy)(NO)](PF6)3, where MeO-Phtpy is the 4′-(4-methoxyphenyl)-2,2′:6′,2″-terpyridine and bpy the 2,2′-bipyridine, has been synthesized and fully characterized. The X-ray crystal structure of the complex is provided together with that of its photoproduct of formula [RuII(MeO-Phtpy)(bpy)(MeCN)](NO3)2. The electronic properties have been investigated theoretically using the time dependent density functional theory (TD-DFT) approach. They reveal that the low-lying electronic transitions exhibit a strong charge transfer character towards the withdrawing nitrosyl unit, which suggest good NO donating capabilities under irradiation performed on a large frequency range. The photorelease of NO has been investigated in acetonitrile at two different wavelengths, λ = 365 and 436 nm, leading to related quantum yields equal to 0.08 and 0.03, respectively. The evolution of the oxidation states of the species involved within the release process is tracked by EPR and 1H NMR spectroscopy. It is confirmed that nitrosyl is released as NO radicals while the related ruthenium(III) photoproduct is readily reduced to ruthenium(II). The mechanism involved in the release is discussed on the basis of the present experimental data and the TD-DFT analysis.