Time-dependent Density Functional Theory Analysis Research Articles

Effect of Flexible, Rigid Planar and Non-Planar Donors on the Performance of Dye-Sensitized Solar Cells

A systematic design and synthesis of three push–pull metal-free organic dyes employing N-alkylated diphenylamine (D1), carbazole (D2), and phenothiazine (D3) as donor moieties are presented in this paper. While, vinylbenzene, methoxybenzene, and cyanoacrylic acid were used as π-linker, auxiliary donor, and acceptor moieties, respectively for all three dyes. The study focusses on identifying the best donor among the three in terms of simple molecular design. TiO2-based dye-sensitized solar cells (DSSC) were fabricated with these dyes. Further, dyes and their deprotonated forms were investigated using density functional theory (DFT) and time-dependent DFT analyses to characterize their electronic and optical properties. The variation in power conversion efficiency (PCE) was observed owing to change in coplanarity from freely rotating diphenylamine, fused planar carbazole, and nonplanar phenothiazine. Cyclic voltammetry was performed on D1, D2, and D3 indicated that the substitution at C3 position is effective in stabilizing the radical cation formed upon exposure to light, thereby preventing it from dimerization and degradation. Results illustrated that the dye-containing carbazole as donor (D2d) delivered the best PCE, viz., 3.7%. This was further enhanced to 4.2% on addition of chenodeoxycholic acid as a coadsorbent.

Effect of functionalization of boron nitride flakes by main group metal clusters on their optoelectronic properties

The possibility of functionalizing boron nitride flakes (BNFs) with some selected main group metal clusters, viz. OLi4, NLi5, CLi6, BLI7 and Al12Be, has been analyzed with the aid of density functional theory (DFT) based computations. Thermochemical as well as energetic considerations suggest that all the metal clusters interact with the BNF moiety in a favorable fashion. As a result of functionalization, the static (first) hyperpolarizability () values of the metal cluster supported BNF moieties increase quite significantly as compared to that in the case of pristine BNF. Time dependent DFT analysis reveals that the metal clusters can lower the transition energies associated with the dominant electronic transitions quite significantly thereby enabling the metal cluster supported BNF moieties to exhibit significant non-linear optical activity. Moreover, the studied systems demonstrate broad band absorption capability spanning the UV–visible as well as infra-red domains. Energy decomposition analysis reveals that the electrostatic interactions principally stabilize the metal cluster supported BNF moieties.

Ground State and Excited State Tuning in Ferric Dipyrrin Complexes Promoted by Ancillary Ligand Exchange.

Three ferric dipyrromethene complexes featuring different ancillary ligands were synthesized by one electron oxidation of ferrous precursors. Four-coordinate iron complexes of the type (ArL)FeX2 [ArL = 1,9-(2,4,6-Ph3C6H2)2-5-mesityldipyrromethene] with X = Cl or tBuO were prepared and found to be high-spin (S = 5/2), as determined by superconducting quantum interference device magnetometry, electron paramagnetic resonance, and 57Fe Mössbauer spectroscopy. The ancillary ligand substitution was found to affect both ground state and excited properties of the ferric complexes examined. While each ferric complex displays reversible reduction and oxidation events, each alkoxide for chloride substitution results in a nearly 600 mV cathodic shift of the FeIII/II couple. The oxidation event remains largely unaffected by the ancillary ligand substitution and is likely dipyrrin-centered. While the alkoxide substituted ferric species largely retain the color of their ferrous precursors, characteristic of dipyrrin-based ligand-to-ligand charge transfer (LLCT), the dichloride ferric complex loses the prominent dipyrrin chromophore, taking on a deep green color. Time-dependent density functional theory analyses indicate the weaker-field chloride ligands allow substantial configuration mixing of ligand-to-metal charge transfer into the LLCT bands, giving rise to the color changes observed. Furthermore, the higher degree of covalency between the alkoxide ferric centers is manifest in the observed reactivity. Delocalization of spin density onto the tert-butoxide ligand in (ArL)FeCl(OtBu) is evidenced by hydrogen atom abstraction to yield (ArL)FeCl and HOtBu in the presence of substrates containing weak C-H bonds, whereas the chloride (ArL)FeCl2 analogue does not react under these conditions.

Cyclometalated Iridium(III) Complexes Containing 4,4'-π-Conjugated 2,2'-Bipyridine Derivatives as the Ancillary Ligands: Synthesis, Photophysics, and Computational Studies.

This article demonstrates a series of cyclometalated Ir(III) complexes of the type [Ir(III)(C^N)2(N^N)](PF6), where C^N is 2-phenylpyridine, and N^N corresponds to the 4,4'-π-conjugated 2,2'-bipyridine ancillary ligands. All these compounds were synthesized through splitting of the binuclear dichloro-bridged complex precursor, [Ir(C^N)2(μ-Cl)]2, with the appropriate bipyridine ligands followed by the anion exchange reaction. The linear and nonlinear absorption properties of the synthesized complexes were investigated. The absorption spectra of all the title complexes exhibit a broad structureless feature in the spectral region of 350-700 nm with two bands being well-resolved in most of the cases. The structures of all the compounds were modeled in dichloromethane using the density functional theory (DFT) algorithm. The nature of electronic transitions was further comprehended on the basis of time-dependent DFT analysis, which indicates that the origins of various bands are primarily due to intraligand charge transfer transitions along with mixed-metal and ligand-centered transitions. The synthesized compounds are found to be nonemissive at room temperature because of probable nonradiative deactivation pathways of the T1 state that compete with the radiative (phosphorescence) decay modes. However, the frozen solutions of compounds Ir(MS 3) and Ir(MS 5) phosphoresce at the near-IR region, the other complexes remaining nonemissive up to 800 nm wavelength window. The two-photon absorption studies on the synthesized complexes reveal that values of the absorption cross-section are quite notable and lie in the range of 300-1000 GM in the picosecond case and 45-186 GM in the femtosecond case.

Ligand K-edge XAS, DFT, and TDDFT analysis of pincer linker variations in Rh(i) PNP complexes: reactivity insights from electronic structure.

Here we report P K-edge, Cl K-edge, and Rh L3-edge X-ray absorption spectroscopy (XAS) data for Rh[C5H3N-2,6-(XP(t)Bu2)2]Cl, where X = O ((tBu)PONOP; ) or CH2 ((tBu)PNP; ). Solid-state XAS data for and were compared to density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations to identify how changing the PNP pincer linker from O to CH2 affected electronic structure and bonding at Rh(i). Pronounced differences in XAS peak intensities and energies were observed. The P K-edge XAS data revealed a large increase in Rh 4dx(2)-y(2) and P 3p orbital-mixing (Rh-P σ*) in compared to , and pronounced transition energy variations reflected marked differences in orbital energies and compositions. By comparison, the Cl K-edge XAS data revealed only subtle differences in Rh-Cl covalency, although larger splitting between the Rh-Cl π* and σ* transitions was observed in . Analysis of the occupied MOs from DFT (HOMO, HOMO-1, HOMO-2, and HOMO-3) and comparison to the unoccupied MOs involved in XAS revealed a relatively uniform energy increase (ca. 0.3-0.5 eV) for all five 4d-derived molecular orbitals in Rh((tBu)PNP)Cl () compared to Rh((tBu)PONOP)Cl (). The energy shift was relatively invariant with respect to differences in orbital symmetry, bonding type (σ or π), and orbital mixing, which suggested that the increase could be attributed to electrostatic effects. The change in d-orbital energies are consistent with known reactivity differences of Rh((tBu)PONOP)(+) and Rh((tBu)PNP)(+) towards CO, H2, and CH2Cl2, and are explained here by considering how d-orbital energies affect covalent L → M σ bonding and M → L π backbonding.

Highly-selective absorption control in photosynthetic chlorin dyes

Selective chemical control of light-absorption bands of dye molecules in which the wavelengths of two or more absorption bands are individually controlled by chemical modifications is an ultimate challenge in chemistry and an important subject for their wide applications. Recently, selective absorption tuning was first reported in photosynthetic bacteriochlorin dyes. In the bacteriochlorin dyes, either the visible or near IR band is selectively shifted by the chemical modifications almost retaining the other band. Fujisawa et al. clarified that the selective absorption tuning is accomplished by chemical control of configuration interactions in the two two-level systems. This paper reports on more highly-selective absorption tuning in photosynthetic chlorin dyes, bacteriochlorophylls (BChls) d and e and the mechanism. In BChls d and e, the near UV band (so-called Soret band) is selectively red-shifted by the chemical modifications of BChl d involving the formylation and methylation perfectly retaining the visible band (so-called Qy). Density functional theory (DFT) and time-dependent DFT analyses showed that the red-shift of the Soret band is predominantly attributed to the large stabilization of the second lowest unoccupied molecular orbital induced by the formylation. In contrast, the Qy absorption retention results from the perfect cancellation between the positive excitation-energy change due to the formylation and negative excitation-energy change due to the methylation, both of which are significantly contributed by configuration interactions. This work reveals that the highly-selective absorption control in BChls d and e is accomplished by the complicated control of configuration interactions in the four-level system.

Mechanism of Co-C bond photolysis in the base-on form of methylcobalamin.

A mechanism of Co-C bond photodissociation in the base-on form of the methylcobalamin cofactor (MeCbl) has been investigated employing time-dependent density functional theory (TD-DFT), in which the key step involves singlet radical pair generation from the first electronically excited state (S1). The corresponding potential energy surface of the S1 state was constructed as a function of Co-C and Co-Naxial bond distances, and two possible photodissociation pathways were identified on the basis of energetic grounds. These pathways are distinguished by whether the Co-C bond (path A) or Co-Naxial bond (path B) elongates first. Although the final intermediate of both pathways is the same (namely a ligand field (LF) state responsible for Co-C dissociation), the reaction coordinates associated with paths A and B are different. The photolysis of MeCbl is wavelength-dependent, and present TD-DFT analysis indicates that excitation in the visible α/β band (520 nm) can be associated with path A, whereas excitation in the near-UV region (400 nm) is associated with path B. The possibility of intersystem crossing, and internal conversion to the ground state along path B are also discussed. The mechanism proposed in this study reconciles existing experimental data with previous theoretical calculations addressing the possible involvement of a repulsive triplet state.

Study on conformational stability, molecular structure, vibrational spectra, NBO, TD-DFT, HOMO and LUMO analysis of 3,5-dinitrosalicylic acid by DFT techniques

In this work we analyzed the vibrational spectra of 3,5-dinitrosalicylic acid (3,5DNSA) molecule. The total energy of eight possible conformers can be calculated by Density Functional Theory with 6-31G(d,p) as basis set to find the most stable conformer. Computational result identify the most stable conformer of 3,5DNSA is C6. The assignments of the vibrational spectra have been carried out by computing Total Energy Distribution (TED). The molecular geometry, second order perturbation energies and Electron Density (ED) transfer from filled lone pairs of Lewis base to unfilled Lewis acid sites for 3,5-DNSA molecular analyzed on the basis of Natural Bond Orbital (NBO) analysis. The formation of inter and intramolecular hydrogen bonding between OH and COOH group gave the evidence for the formation of dimer formation for 3,5-DNSA molecule. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) complements with the experimental findings. The simulated spectra satisfactorily coincides with the experimental spectra.

Vibrational spectra (FT-IR and FT-Raman), molecular structure, natural bond orbital, and TD-DFT analysis of l-Asparagine Monohydrate by Density Functional Theory approach

In this work we report the vibrational spectral analysis of l-Asparagine Monohydrate (LAM) molecule by using FT-IR and FT-Raman spectroscopic techniques. The equilibrium geometry, harmonic vibrational wavenumbers, various bonding features have been computed using density functional B3LYP method with 6-311G(d,p) as basis set. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. The results show that charge in electron density (ED) in σ* and π* antibonding orbitals and second order delocalization energies E(2) confirms the occurrence of Intramolecular Charge Transfer (ICT) within the molecule. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) complements with the experimental findings. The simulated spectra satisfactorily coincide with the experimental spectra.

Photosolvolysis ofcis-[Ru(α-diimine)2(4-aminopyridine)2]2+Complexes: Photophysical, Spectroscopic, and Density Functional Theory Analysis

The photochemical and photophysical properties of the cis-[Ru(II)(α-diimine)2(4-APy)2](2+) complexes, where α-diimine = 1,10-phenanthroline (phen) and 4-APy = 4-aminopyridine I, 4,7-diphenyl-1,10-phenanthroline (Ph2phen) II, 2,2'-bipyridine (bpy) III, and 4,4'-dimethyl-2,2'-bipyridine (Me2bpy) IV, are reported. The four complexes were characterized using high-performance liquid chromatography, (1)H NMR, UV-visible, emission, and transient absorption spectroscopy. Upon photolysis in acetonitrile solution these complexes undergo 4-APy dissociation to give the monoacetonitrile complex (for II, III, and IV) or the bis(acetonitrile) complex (for I). A fairly wide range of excitation wavelengths (from 420 to 580 nm) were employed to explore the photophysics of these systems. Quantum yields and transient spectra are provided. Density functional theory (DFT) and time-dependent DFT analysis of singlet and triplet excited states facilitated our understanding of the photochemical behavior. A detailed assessment of the geometric and electronic structures of the lowest energy spin triplet charge transfer state ((3)MLCT) and spin triplet metal centered state ((3)MC) (dπ → σ* transitions) for species I-IV is presented. A second, previously unobserved, and nondissociative, (3)MC state is identified and is likely involved in the primary step of photodissociation. This new (3)MC state may indeed play a major role in many other photodissociation processes.

Light-Atom Influences on the Electronic Structures of Iron–Sulfur Clusters

Ligand K-edge X-ray absorption spectroscopy was used to study dimeric and tetrameric Cl-terminated Fe-S clusters with variable numbers of S(2-) substituted by N(t)Bu(2-) (N(t)Bu(2-) = tertbutylimido) ligands to gain insights into the functional role of the interstitial light atom in the iron-molybdenum cofactor (FeMoco) of nitrogenase. These studies are complemented by time-dependent density functional theory analysis to quantify the relative effects on Fe-S and Fe-Cl bonding. The results show that N(t)Bu(2-) substitution dramatically affects the electronic structure of dimeric clusters, while the impact on tetrameric clusters is small. Strong agreement between experiment and theory merited extension of this analysis to hypothetical clusters with S(2-) substituted by N and C-atom donor ligands as well as FeMoco itself. These results show that very strong electron donors are required to appreciably modulate the electronic structure of tetrameric (or larger) iron sulfur clusters, pointing to a possible role of the central C(4-) in FeMoco.

Probing the Electronic Properties of a Trinuclear Molecular Wire Involving Isocyanoferrocene and Iron(II) Phthalocyanine Motifs

A new trinuclear iron(II) complex involving two isocyanoferrocene ligands axially coordinated to iron(II) phthalocyanine, (FcNC)2FePc [Fc = ferrocenyl; Pc = phthalocyaninato(2-) anion], was isolated and characterized using a variety of spectroscopic methods as well as single-crystal X-ray diffraction. The redox behavior of the above molecular wire was investigated through electrochemical, spectroelectrochemical, and chemical oxidation approaches and compared to that of the bis(tert-butylisocyano)iron(II) phthalocyanine reference compound, (t-BuNC)2FePc. For both complexes, the first oxidation involves the phthalocyanine ligand and results in the formation of a red phthalocyanine cation-radical-centered [(RNC)2FePc](+) species, as evidenced by their UV-vis and electron paramagnetic resonance spectra. Despite the ~11.5 Å distance between the isocyanoferrocene iron centers, the second and third oxidation potentials for (FcNC)2FePc are separated by ∼80 mV, which is indicative of a weak long-range metal-metal coupling in this system. Spectroscopic signatures of the mixed-valence [(FcNC)2FePc](2+) dication were obtained using spectroelectrochemical and chemical oxidation approaches. These experimentally assessed characteristics were also correlated with the electronic structure, redox properties, and spectroscopic signatures predicted by density functional theory (DFT) and time-dependent DFT analyses.

Vibrational spectra, molecular structure, natural bond orbital, first order hyperpolarizability, TD-DFT and thermodynamic analysis of 4-amino-3-hydroxy-1-naphthalenesulfonic acid by DFT approach

Vibrational spectral analysis of 4-amino-3-hydroxy-1-naphthalenesulfonicacid (4A3HNSA) molecule were carried out using FT-IR and FT-Raman spectroscopic techniques. The equilibrium geometry, harmonic vibrational wavenumbers, various bonding features have been computed using density functional B3LYP method with 6-31G(d,p) as basis set. The Non-Linear Optical (NLO) behavior of 4A3HNSA has been studied by determination of the electric dipole moment (μ) and hyperpolarizability β using HF/6-31G(d,p) method. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. The results show that charge in electron density (ED) in σ* and π* antibonding orbitals and second order delocalization energies (E2) confirms the occurrence of Intramolecular Charge Transfer (ICT) within the molecule. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) complements with the experimental findings. The simulated spectra satisfactorily coincide with the experimental spectra.

Synthesis, structure, UV–Vis–IR spectra, magnetism and theoretical studies on CuII[(2-aminomethyl)pyridine](thiocyanate)2 and comparisons with an analogous CuII complex

The ligand influenced formation of the title complexes has been discussed in the light of the structure, spectral (IR and UV–Vis), RT magnetic and theoretical studies (DFT and TDDFT). Complex 2 , for which only a structure has been reported previously, has been thoroughly studied and compared with complex 1 with respect to the structure and spectral properties. In the unit cell, the monomeric complex 1 assembles into 2-D layers through very weak non-bonded interactions between anionic S and Cu 2+ , while the octahedral complex 2 assembles into a 2-D layer in the unit cell through the H-bonding interactions between amino H and the anionic S and N3 atom. The TDDFT analysis of the absorption spectra indicate that absorption maxima are at a relatively high energy and are mainly assigned to π → π∗ transitions (in pyridine) with a fair contribution of metal to ligand charge transfer (MLCT) and ligand to ligand charge transfer (LLCT) transitions. All the low lying transitions are categorized as mixed MLCT/LLCT. A very weak but broad band in the higher wavelength region has been detected and identified as a d–d transition band. ► Synthesis and structural details of a new copper complex, CuII[(2-aminomethyl)pyridine](thiocyanate) has been presented. ► The UV–Vis and IR spectra along with the geometrical aspects have been analyzed in depth with the help of theoretical (DFT and TDDFT) calculations. ► In addition, to highlight the ligand influence on the complex formation, Cu[(2-aminomethyl)pyridine]2(SCN)2 was also synthesised, structural and spectral characteristics were fully analyzed and compared with the title complex. The title complex was synthesized under self-assembly conditions using Cu(acetate) 2 ·H 2 O, 2-amp (= 2-aminomethylpyridine) and KSCN, and was characterized by IR, elemental analysis and single crystal structural analysis, and its spectral and RT magnetic properties were investigated. The asymmetric unit consists of a square planar Cu(II) center, with two ligand N atoms and two anionic Ns forming the square plane. In the unit cell, the monomeric complex assembles into 2-D layers through very weak non-bonded interactions between anionic S and Cu 2+ . Further, the structure was satisfactorily modeled by calculations based on Density Functional Theory (DFT), and the UV–Vis and IR spectra are analyzed in depth with the help of Time Dependent DFT (TDDFT). The results indicate that the absorption maxima are at relatively high energy and are mainly assigned to π → π ∗ transitions (in pyridine), with a fair contribution of metal to ligand charge transfer (MLCT) and ligand to ligand charge transfer (LLCT) transitions. All the low lying transitions are categorized as mixed MLCT/LLCT. A very weak but broad band in the higher wavelength region has been detected and identified as a d–d transition band. Also, it has been found that when the ligand ratio is modified, the formation of Cu(2-amp) 2 (SCN) 2 takes place under the same self-assembly conditions, whose structure only has been recently reported. Structural, spectral and theoretical comparisons are presented for both complexes.

Quantum mechanical study of the structure and spectroscopic (FT-IR, FT-Raman, 13C, 1H and UV), first order hyperpolarizabilities, NBO and TD-DFT analysis of the 4-methyl-2-cyanobiphenyl

The Fourier transform infrared (FT-IR) and FT-Raman of 4-methyl-2-cyanobiphenyl (4M2CBP) have been recorded and analyzed. The equilibrium geometry, bonding features and harmonic vibrational frequencies have been investigated with the help of density functional theory (DFT) method. The assignments of the vibrational spectra have been carried out with the help of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). The 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by the Gauge including atomic orbital (GIAO) method. The first order hyperpolarizability ( β 0) of this novel molecular system and related properties ( β, α 0 and Δ α) of 4M2CBP are calculated using HF/6-311G(d,p) method on the finite-field approach. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. The results show that charge in electron density (ED) in the σ* and π* antibonding orbitals and second order delocalization energies ( E 2) confirms the occurrence of intramolecular charge transfer (ICT) within the molecule. UV–vis spectrum of the compound was recorded and the electronic properties, such as HOMO and LUMO energies, were performed by time-dependent density functional theory (TD-DFT) approach. Finally the calculations results were applied to simulated infrared and Raman spectra of the title compound which show good agreement with observed spectra.

Time-dependent density functional theory study of cobalt corrinoids: Electronically excited states of methylcobalamin

Time-dependent density functional theory (TDDFT) has been applied to the analysis of the electronic spectra of methylcobalamin (MeCbl) and its derivative in which the trans axial base was replaced by a water molecule (MeCbi[Single Bond]H(2)O). The latter corresponds to the situation encountered in strongly acidic solutions. The study primarily focuses on the accuracy of two functionals, the hybrid B3LYP and the gradient corrected BP86, in dealing with the electronic excitations. The high resolution crystal structure of MeCbl was the source of the initial coordinates. To generate the initial structures, the full MeCbl was simplified by replacing the corrin side chains by H atoms. The vertical excitation energies, together with the corresponding oscillator strengths, were calculated at the optimized BP86 and B3LYP structures of the ground electronic state of the complexes. The NBO analysis shows that the B3LYP functional gives a bonding description of the ground state as a more polarized covalent bond compared to that given by BP86. The latter functional has more covalent bonding and is thus more appropriate for modeling the axial bonding properties. To validate the accuracy of the present TDDFT analysis, the computed excitations were directly compared to the absorption spectra of MeCbl. In order to obtain a reliable agreement between experiment and theory, the two-parameter scaling technique was introduced, which compensates differently the low-energy and high-energy excitations. Electronic excitations strongly depend on the choice of the functional. Transitions involving corrin pi-->pi(*) excitations are better described by the B3LYP functional while transitions associated with metal-to-ligand (dpi-->pi(*)d) excitations are better described by BP86. These differences can be associated with the different bonding descriptions obtained by B3LYP and BP86.

TD-DFT analysis of the electronic spectra of Ti-containing catalysts

A good correlation between the experimental UV–Vis spectra of titanium containing catalysts and the photo-physical properties calculated using Time-Dependent Density Functional Theory (TD-DFT) has been found. This finding makes the TD-DFT methodology an excellent tool to generate and interpret the electronic spectra of isolated atoms in the surface of heteroatom-containing inorganic substrates.