Time-dependent Density Functional Theory Study Research Articles

Synthesis, crystal structures, optical properties, DFT and TD-DFT studies of Ni (II) complexes with imine-based ligands

Two new square-planar nickel (II) complexes were synthesized from (2-((E)-(9-ethyl-9H-carbazol-7-ylimino)methyl)phenol) and (1-((E)-(9-ethyl-9H-carbazol-7-ylimino)methyl)naphthalen-2-ol) ligands, for complex I and complex II, respectively. They were characterized by IR, UV-Vis spectroscopy and X-ray diffraction. Further measurements were also conducted as cyclic voltammetry and conductivity measurements. Both complexes crystallize in the monoclinic system with the space groups P21/n and P21/c for complex I and complex II, respectively. The electronic absorption spectrum of complex I exhibits the lowest-lying absorption band (LEB) at 381 nm and the highest energy absorption band (HEB) at 269 nm. For complex II, the LEB was located at 431 nm while the HEB was found to be at 260 nm. Theoretical structure geometries, vibrational frequencies and electronic properties of the two complexes were calculated, by means of the density functional theory (DFT). The basis set 6-31g+(d) was chosen, for non-metal atoms (C, H, N and O) and the Stuttgart/Dresden effective core potentials basis set (SDD), for Ni atoms. UV-Vis transitions nature was investigated via a time-dependent density functional theory (TD-DFT) calculation. Overall, theoretical calculations were in accordance with the experimental results.

DFT and TDDFT Study of the Reaction Pathway for Double Intramolecular C-H Activation and Functionalization by Iron, Cobalt, and Nickel-Nitridyl Complexes.

Previous work was successful in synthesizing a nickel amine, [CztBu(PyriPr)(NH2-PyriPr)], by double C-H activation and functionalization via irradiating a disphenoidal Ni(II) azido complex, [CztBu(PyriPr)2NiN3]. The present work seeks to expand upon the earlier research and to substitute the metal with iron or cobalt. Density functional theory (DFT)-B3LYP/6-31+G(d') and APFD/Def2TZVP-was used to simulate the generation of an intermediate with significant nitridyl radical character after the loss of N2 from the starting azido complex. DFT and time-dependent density functional theory (TDDFT) were also used to propose a detailed pathway comprised of intermediates of low, intermediate, or high spin multiplicity and photogenerated excited states for the reaction of the azido complex, [CztBu(PyriPr)2MN3], to form the amine complex [CztBu(PyriPr)M(NH2-PyriPr)], M = Co, Ni, or Fe.

Investigating functional performance and substituent effect in modelling molecular structure, UV-visible spectra, and optical properties of D-π-A conjugated organic dye molecules: a DFT and TD-DFT study

The molecular structure, UV-visible spectra, and optical properties of D-π-A conjugated organic dye molecules (Disperse Red 1 (DR1) and Disperse Red 73 (DR73)) were analyzed using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) and compared with azobenzene molecule to study the effect of donor and acceptor substituents on the molecular properties. The performance of DFT functionals is investigated using B3LYP hybrid functional and three long-range corrected functionals (CAM-B3LYP, LC-ω PBE, and ω B97XD) in conjunction with 6-31G(d,p) basis set. Using TD-DFT, we calculate the vertical excitation energies and transition dipole moment values for 100 excited states. These values were further utilized to calculate frequency dependent polarizability under sum-over-states (SOS) formalism and refractive index of these molecular systems. We observe that for azobenzene and DR1 molecules, ω B97XD predicted wavelengths corresponding to peak absorbance closest to the experimental results, while for DR73 molecule, B3LYP gave better prediction. Large polarizability response is also observed for these molecules (DR1 and DR73) in comparison to parent azobenzene structure due to charge transfer between donor and acceptor groups. For DR1 and DR73 molecules, αxx component of polarizability dominates in contrast to azobenzene where αyy dominates. The HOMO → LUMO transition during excitation contributes to the peak molecular response in simulated UV-visible spectra. The high polarizability response of selected D-π-A conjugated molecules in comparison to parent molecule suggests that these molecules are promising candidates for tailor-made photonic and optoelectronic device development. Graphical Abstract Functional and substituent effect on the optical response of D-π-A conjugated molecules modelled using DFT and TDDFT.

Bis(CBT)palladium(II) Derivatives (CBT = m-carborane-1-thiolate): Synthesis, Molecular Structure, and Physicochemical Properties of cis-[(bipy)Pd(CBT)2] and trans-[(py)2Pd(CBT)2

The new synthesized PdII complex cis-[(bipy)Pd(CBT)2] (bipy = 2,2'-bipyridyl; CBT = m-carborane-1-thiolate anion), which is a potential BNCT (boron neutron capture therapy) agent and of structure elucidated by single-crystal X-ray work, has been studied by infrared (IR) and ultraviolet-visible light (UV-vis) spectra and its properties compared with those of the previously reported and also the structurally characterized analogue trans-[(py)2Pd(CBT)2]. This trans species, prepared via a direct method, was previously isolated from a pyridine solution, consequent to the occurring releasing of the external Pd(CBT)2 moieties of the porphyrazine macrocycle [{Pd(CBT)2}4LZn]·xH2O (L = tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazinato anion), which is an active photosensitizer in photodynamic therapy (PDT) and a potential bimodal PDT/BNCT agent. The UV-vis spectral behavior of both cis and trans species in CHCl3 solution and in the gas phase has been examined in detail by density functional theory (DFT) and time-dependent density functional theory (TDDFT) studies devoted to explain their distinct behavior observed in the region of 400-500 nm, as determined by the presence in the cis structure of a vicinal arrangement of the two CBT groups, an ensemble of results closely similar to those observed for the macrocycles [{Pd(CBT)2}4LM]·xH2O (M = MgII(H2O), ZnII, PdII). It has also been experimentally proved the tendency of the cis isomer in CHCl3/pyridine solution to be changed to the respective trans analogue, with conversion occurring in two steps, as interpreted by detailed DFT studies.

π‑Extended Boron Difluoride [NՈNBF2] Complex, Crystal Structure, Liquid NMR, Spectral, XRD/HSA Interactions: A DFT and TD-DFT Study

The novel tetrahedral 10-(4-carboxyphenyl)-2,8-diethyl-5,5-difluoro-1,3,7,9-tetramethyl- 5H-di-pyrrolo[1,2-c:2',1'-f][1,3,2]diazaborinin-4-ium-5-uide [NՈNBF2] BODIPY complex was prepared in a very good yield and via one-pot synthesis. The desired [NՈNBF2] has been used as a model complex for XRD/HSA interactions and DFT/B3LYP/6-311G(d,p) computations. The tetrahedral geometry around the boron center was demonstrated by DFT optimization and XRD-crystallography. The 1H, 11B, and 19F-NMR spectra were used also to support the high symmetrical BODIPY via π‑extended phenomena. Moreover, the values of the DFT-calculated structural bond lengths/angles and DFT-IR were matched to the corresponding experimental XRD and IR parameters, respectively. The crystal lattice interactions were correlated to Hirshfeld surface analysis (HSA) calculations. Calculations of the Mulliken Atomic Charge (MAC), Natural Population Analysis (NPA), Global reactivity descriptors (GRD), and Molecular Electrostatic Potential (MEP) quantum parameters were performed to support the XRD/HSA interactions result. Analysis of the predicted Density of States (DOS), molecular orbital, and time-dependent density functional theory (TD-DFT) calculations have been combined to explain the experimental UV-vis spectra and electron transfer behavior in [NՈNBF2] complex using MeOH and other four solvents.

The effect of ring aromaticity on ESIPT behavior and photophysical properties of 2-(2′-hydroxyphenyl)- 4-chloromethylthiazole derivatives: A TD-DFT study

By using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods, the effect of ring aromaticity on the excited state intramolecular proton transfer (ESIPT) process and photophysical properties of HCO, HCSe, HPDCT and HPZCT compounds were explored in detail. The strengthened excited state intramolecular hydrogen bonds (Hbonds) of the studied compounds were confirmed by analysis of the structure, infrared vibration frequency, electron density and reduced density gradient. The stronger Hbond is favorable to ESIPT process. Frontier molecular orbitals evidently showed that the proton transfer was induced by the rearrangement of electronic density. The HOMO-LUMO energy gap (Egap) correlated with the Stokes shift in the enol form. A smaller Egap would produce a larger Stokes shift. The heteroatom substitution in thiazole ring and nitrogen substitution in benzene ring of HCT molecule affected the ring aromaticity, and then had an obvious effect on the intramolecular Hbond. The stronger the ring aromaticity, the stronger the intramolecular Hbond, and the easier the ESIPT process to occur.

A time-dependent density functional theory study of a fluorescent probe to detect hydroxyl radicals: Inhibiting the twisted intramolecular charge-transfer process

Due to the relevance to excited-state processes, sensing mechanisms of fluorescent probes were difficult to study directly by experimental methods. This work investigated theoretically the sensing mechanism of a reported bifunctional fluorescent probe to detect intracellular hydroxyl radicals and their environmental viscosity (J. Am. Chem. Soc. 2019, 141, 18301). Calculations were performed at the B3P86/TZVP/SMD level using density functional theory and time-dependent density functional theory. The transition from the ground-state (S0) to the first singlet excited state (S1) was calculated to have the largest oscillation strength for the probe. The wavelength that corresponded to the S0-S1 vertical excitation energy (427 nm) agreed well with the maximum absorption band at 400 nm in the ultraviolet–visible spectra. Theoretical results showed that the probe had two distinct geometries in the S0 and S1 states, respectively. This difference was caused by the different distributions of frontier molecular orbitals that were involved in the S0-S1 transition and corresponds to a twisted intramolecular charge transfer. The S1-state potential energy curve of the probe molecule confirmed that the twisted intramolecular charge transfer could proceed spontaneously with a potential barrier of only 12.20 kJ/mol. This result provided an irradiative approach for the probe molecule to dissipate the S1-state energy, which explained its fluorescence quenching. In contrast, the hydroxyl oxidation reaction changed frontier molecular orbitals of the probe molecule, which made its S1 state a local S1 state with a strong fluorescence emission. Precisely due to the mechanism, the hydroxyl radicals could be detected by changes in the fluorescence signal of the probe molecule.

Vibronic absorption spectrum and electronic properties of methylene blue in aqueous solution: TD-DFT study

The vibronic absorption spectrum of methylene blue (MB) in an aqueous solution is calculated using the time-dependent density functional theory (TD-DFT). The results of calculations are analyzed using all hybrid functionals supported by Gaussian16, the 6–31++G(d,p) basis set and the IEFPCM and SMD solvent models. The solvent model IEFPCM gave significantly underestimated values of λmax in comparison with the experiment. This is a manifestation of the TD-DFT “cyanine failure”. However, the SMD model made it possible to obtain good agreement between the calculation results and experimental data. The best fit was achieved using the X3LYP functional. According to our calculations, the shoulder in the visible absorption spectrum of MB has a vibronic origin. Explicit assignment of a water molecule strongly bound to the N10 endocyclic nitrogen atom does not change the shape of the absorption band, but shifts its maximum by 7 nm to the long-wavelength region of the spectrum. The dipole moments and atomic charges of the ground and excited states of the MB molecule have been calculated. Photoexcitation leads to an increase in the dipole moment of the dye molecule. An insignificant photoinduced electron transfer was found in the central ring of the chromophore of the dye molecule. In accordance with our results, the absorption peak of the MB solution in the visible region of the spectrum is due to the π → π* type electronic transition. Vibronic coupling plays a significant role in the absorption spectra of MB.

Excited electron dynamics in the interface of 2H-1T hetero-phases of monolayer MoS2: time-dependent density functional theory study

Excited electron dynamics in the interface of 2H-1T hetero-phases of monolayer MoS2: time-dependent density functional theory study

Effects of Structural Dynamics on Charge Carrier Transfer in B-DNA: A Combined MD and RT-TDDFT Study.

Hole transfer along the axis of duplex DNA has been the focus of physical chemistry research for decades, with implications in diverse fields, from nanotechnology to cell oxidative damage. Computational approaches are particularly amenable for this problem, to complement experimental data for interpretation of transfer mechanisms. To be predictive, computational results need to account for the inherent mobility of biological molecules during the time frame of experimental measurements. Here, we address the structural variability of B-DNA and its effects on hole transfer in a combined molecular dynamics (MD) and real-time time-dependent density functional theory (RT-TDDFT) study. Our results show that quantities that characterize the charge transfer process, such as the time-dependent dipole moment and hole population at a specific site, are sensitive to structural changes that occur on the nanosecond time scale. We extend the range of physical properties for which such a correlation has been observed, further establishing the fact that quantitative computational data on charge transfer properties should include statistical averages. Furthermore, we use the RT-TDDFT results to assess an efficient tight-binding method suitable for high-throughput predictions. We demonstrate that charge transfer, although affected by structural variability, on average, remains strong in AA and GG dimers.

Red-Purple Photochromic Indigos from Green Chemistry: Mono-tBOC or Di-tBOC N-Substituted Indigos Displaying Excited State Proton Transfer or Photoisomerization.

In indigo, excited state proton transfer (ESPT) is known to be associated with the molecular mechanism responsible for highly efficient radiationless deactivation. When this route is blocked (partially or totally), new deactivation routes become available. Using new green chemistry procedures, with favorable green chemistry metrics, monosubstitution and disubstitution of N group(s) in indigo, by tert-butoxy carbonyl groups, N-(tert-butoxycarbonyl)indigo (NtBOCInd) and N,N'-(tert-butoxycarbonyl)indigo (N,N'tBOCInd), respectively, were synthetically accomplished. The compounds display red to purple colors depending on the solvent and substitution. Different excited-state deactivation pathways were observed and found to be structure- and solvent-dependent. Trans-cis photoisomerization was found to be absent with NtBOCInd and present with N,N'tBOCInd in nonpolar solvents. Time-resolved fluorescence experiments revealed single-exponential decays for the two compounds which, linked to time-dependent density functional theory (TDDFT) studies, show that with NtBOCInd ESPT is extremely fast and barrierless-predicted to be 1 kJ mol-1 in methylcyclohexane and 5 kJ mol-1 in dimethylsulfoxide-, which contrasts with ∼11 kJ mol-1 experimentally obtained for indigo. An alternative ESPT, competitive with the N-H···O═C intramolecular pathway, involving dimer units is also probed by TDDFT and found to be consistent with the experimentally observed time-resolved data. N,N'tBOCInd, where ESPT is precluded, shows solvent-dependent trans-cis/cis-trans photoisomerization and is surprisingly found to be more stable in the nonemissive cis conformation, whose deactivation to S0 is found to be solvent-dependent.

Novel donor–acceptor non-fullerene metal–organic solar cells based on open edge Sc@BN: a DFT and TD-DFT study

The organic solar cells (OSCs) have been increasingly attractive due to their environmental issues, flexibility, economic advantages, designing and productions. First generation of these systems was commonly based on the fullerene structures. In this work, four donor–acceptor (D–A) systems using Sc-doped BN layer as the non-fullerene acceptor and alpha-sexithiophene as donor were investigated, and the efficiency of OSCs was assessed by application of density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculation methods. The results show that the systems were the superior by the highest and longest charge transfer from donor (D) to acceptor (A). According to the obtained results, two systems could just be applied as OSCs, which the highest anticipated voltage was 2.3 eV in them. Furthermore, the effective absorption range was about 100 nm in photoinduced electron transfer (PET) or charge transfer process at the end of ultraviolet (UV) region.

DFT and TDDFT studies of the new inorganic perovskite CsPbI3 for solar cell applications

In this paper, the density functional theory (DFT) and time-dependent density-functional theory (TDDFT) have been used to study the structural, electronic and optical properties of the inorganic perovskite CsPbI3 material. This compound has its applications in the solar cell solicitations. The CsPbI3-based perovskite solar cell (PSC) device has high efficiency together with improved stability. Special attention is paid, in this work, to the effect of spin orbit coupling on the electronic and optical performance of this compound. Using GGA-PBESol method, it is shown that the energy gap value decreases with Spin orbit coupling. In fact, when applying the GGA-PBESol method without SOC approximation, we found a band gap energy value of 1.16 eV. When adding the SOC correction, it is found that the band gap energy value decreases to reach the value 0.39 eV. On the other hand, the studied system exhibits a high absorption in the visible region of the electromagnetic radiations.We studied the effect of GGA-PBESol method with and without Spin orbit coupling, and found that the effect of adding the SOC correction is to decrease the energy gap value. In fact, when applying the GGA-PBESol method without SOC approximation, we found a band gap energy value of 1.16 eV. When adding the SOC correction, it is found that the band gap energy value decreases to reach the value 0.39 eV.

Donor acceptor fluorophores: synthesis, optical properties, TD-DFT and cytotoxicity studies.

Donor-π-acceptor (D-π-A) fluorophores consisting of a donor unit, a π linker, and an acceptor moiety have attracted attention in the last decade. In this study, we report the synthesis, characterization, optical properties, TD-DFT, and cytotoxicity studies of 17 near infrared (NIR) D-π-A analogs which have not been reported so far to the best of our knowledge. These fluorophores have chloroacrylic acid as the acceptor unit and various donor units such as indole, benzothiazole, benzo[e]indole, and quinoline. The fluorophores showed strong absorption in the NIR (700-970 nm) region due to their enhanced intramolecular charge transfer (ICT) between chloroacrylic acid and the donor moieties connected with the Vilsmeier-Haack linker. The emission wavelength maxima of the fluorophores were in between 798 and 870 nm. Compound 20 with a 4-quinoline donor moiety showed an emission wavelength above 1000 nm in the NIR II window. The synthesized fluorophores were characterized by 1H NMR and 13C NMR, and their optical properties were studied. Time dependent density functional theory (TD-DFT) calculations showed that the charge transfer occurs from the donor groups (indole, benzothiazole, benzo[e]indole, and quinoline) to the acceptor chloroacrylic acid moiety. Fluorophores with [HOMO] to [LUMO+1] transitions were shown to possess a charge separation character. The cytotoxicity of selected fluorophores, 4, 7, 10 and 12 was investigated against breast cancer cell lines and they showed better activity than the anti-cancer agent docetaxel.

Magnetic Circular Dichroism of Naphthalene Derivatives: A Coupled Cluster Singles and Approximate Doubles and Time-Dependent Density Functional Theory Study.

The UV-vis absorption and magnetic circular dichroism spectra of naphthalene and some of its derivatives have been simulated at the Coupled Cluster Singles and Approximate Doubles (CC2) level of theory, and at the Time-Dependent Density Functional Theory (TD-DFT) level using the B3LYP and CAM-B3LYP functionals. DFT and CC2 predict in general opposite energetic ordering of the Lb and La transitions (in gas phase), as previously observed in adenine. The CC2 simulations of UV and MCD spectra show the best agreement with the experimental data. Analysis of the Cartesian components of the electric dipole transition strengths and the magnetic dipole transition moment between the excited states have been considered in the interpretation of the electronic transitions and the Faraday term inversion among the naphthalene derivatives.

Benzophenone based photostable fluorescent monoazo disperse dyes: Synthesis, AIE, viscosity, UPF and TD-DFT study

Synthesis of a parallel series of hydrophobic azo dyes (4-hydroxy benzophenone and corresponding 4-methoxy benzophenone series) and a comprehensive systematic spectroscopic study in solvents of varying polarity and viscosity is presented. This includes glycerol-dimethylsulfoxide, toluene–polyethylene glycol 400 and toluene–paraffin oil viscous mixtures. Emission intensities of dyes (hydrazone forms) were enhanced by 47–96 folds in viscous solvent media compared to the non-viscous media. So, role of hydrogen bonding in the emission enhancement were verified for 4-hydroxy benzophenone series with 4-methoxy benzophenone series. Polarity alteration effect on spectroscopic properties of dyes in various viscous combinations has been correlated by solvent polarity graphs. Density Functional Theory (DFT), Time Dependent Density Functional Theory (TD-DFT), HOMO–LUMO energy gap and Electrophilicity-index estimations are in good contract with the experimental interpretations. Dyes on PET fibers showed excellent light fastness. Moreover, all the dyes on dyed fabrics exhibited good sublimation fastness and color values. Ultraviolet A/Ultraviolet B blocking and Ultraviolet Protection Factor (UPF) of all the dyes range 15–50 and are in good agreement with light fastness.

Water-vapochromic behavior of a mononuclear Pd(II) complex of piroxicam: A DFT and TD-DFT study

The vapochromic behavior of a mononuclear Pd(II) complex with piroxicam ligands (trans-[Pd(Pir)2] (Pir− is piroxicam anion)) in the presence of water vapor has been theoretically investigated using the time-dependent density functional theory (TD-DFT). The structure of Pd(II) complex interacting with different number of water molecules (n = 1–5) was optimized, separately. The electronic absorption spectra of the optimized structures were calculated using the TD-DFT method and the changes in the absorption spectrum of complex with the increase in the number of water molecules were followed. Comparison of the absorption spectrum of bare Pd(II) complex with those of its hydrated forms with different numbers of water molecules showed a considerable change in the region of 360–400 nm including the change in the intensity and peak position. The main electronic configurations of the intense absorption lines in the related absorption spectra were determined so that the molecular orbitals involved in these absorption lines were determined. The natural bonding orbital (NBO) analysis was performed to assign the NBOs contributing to these molecular orbitals and to see how the NBO composition of the involved molecular orbitals in the electron excitation change with the number of water molecules. It was observed that the change in the intensity and position of the inter- and intraligand π→π∗ transitions are responsible for the color change. Also, based on the NBO results, the contribution of the electronic transitions involving the Pd(II) ion in the color change of the complex was absent.

Sensing mechanism of fluorogenic urea with fluoride in solvent media: A new fluorescence quenching mechanism.

The interaction of 1-Phenyl-3-(pyren-1-yl) urea (LH) and fluoride anion (F-) with a unique ON1-OFF-ON2 fluorescent response has been investigated by the density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations. The hydrogen-bonding dynamics and photophysical properties of the complex LH-F, as well as its isolated receptor LH and anion form L-H1, have been studied in detail. We demonstrate that the intermolecular hydrogen bond (N-H…F) of the complex LH-F is greatly enhanced in the electronically excited state. The nonradiative deactivation via electron transfer and internal conversion rather than excited-state intramolecular proton transfer (ESIPT) can be facilitated by the excited state hydrogen bond strengthening. The results have been cross-validated by molecular structure, electronic spectra, frontier molecular orbitals, and infrared spectra as well as hydrogen bond binding energy. These results indicate that the current calculations completely reproduce the experimental results and provide compelling evidence for the sensing mechanism of LH for F-.

A TD-DFT study of the excited dissociative electronic states of the DNA nucleobases bound to Li+

In this work, the first and second dissociative potential curves of adenineLi+ (ADLi+), guanineLi+ (GUALi+), cytosineLi+(CYTLi+), and thymineLi+ (THYLi+) complexes, related to the dissociation of their LiO and LiN bonds, have been calculated in the gas phase and water, separately. For this purpose, the fifteen excited potential curves, in order of increasing energy, were calculated for each complex and the dissociative potential curves were distinguished from them considering the conical intersection points. The time-dependent density functional theory (TD-DFT) method employing the M06-2X functional was used for the calculations. It was observed that the electron transfer from the DNA base to the Li+ took place during the dissociation of complexes in the gas phase. The electrostatic field of water blocked this charge transfer and led to the excited DNA base and Li+ in its ground state. The vertical excitation energy for the desorption of the Li fragment as a neutral and cation species from the DNA bases was determined. The effect of the interaction site of Li+ on the dissociative potential curves was also investigated.

Time-dependent density functional theory study of the X-ray emission spectroscopy of amino acids and proteins

The non-resonant X-ray emission spectroscopy of amino acids and a dipeptide have been studied using time-dependent density functional theory (TDDFT) calculations at the nitrogen and oxygen K-edges. Comparison with higher level calculations and experimental data shows that TDDFT with the CAM-B3LYP exchange–correlation functional and (Z+1)6-311G* basis set provides an accurate description of the spectra. Calculations for model α-helix and β-sheet structures show the spectra to relatively insensitive to the structure of peptide bond, with the greatest variation observed at the oxygen K-edge.