Time-dependent Density Functional Theory Approach Research Articles

DFT and TD-DFT calculations on thieno[2,3-b]indole-based compounds for application in organic bulk heterojunction (BHJ) solar cells

Eight novel organic compounds with donor–π–acceptor (D–π–A) structure were designed for use as donors in organic bulk heterojunction (BHJ) solar cells. The molecules have thieno[2,3-b]indole as donor, methylene malononitrile as electron acceptor group, and a π-spacer bridge based on thiophene and benzene or its derivatives. The designed compounds were studied using density functional theory (DFT) and time-dependent DFT approaches, to shed light on how the π-conjugation order influences the performance of corresponding photovoltaic solar cells. The study includes prediction of the energy of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels, the energy gap, Voc (the open-circuit voltage), the λmax of absorption, and other quantum-chemical parameters. The results show that, the greater the number of thiophenes present in the bridge, the better the compound as a donor for BHJ solar cells. The theoretical power conversion efficiency calculated for the designed products reaches 6%.

Theoretical insights into co-sensitization mechanism in Zn-porphyrin and Y123 co-sensitized solar cells

Donor-π-acceptor YD2-o-C8, WW-6, and SM315 are among best-performing Zn-porphyrins for their outstanding light-harvesting properties. To reach the further enhancement of photovoltaic performance of the corresponding cells, co-sensitization of these typical porphyrins with those dyes possessing intense absorption in the green spectral region (typically, Y123) is necessary. In this work, using density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches, co-sensitization mechanism in the above three typical Y123/Zn-porphyrin systems has been systematically investigated. Moreover, due to the excellent performance of dithienosilole (DTS) group in organic dyes, it is designed here to replace the benzothiadiazole (BTD) unit in SM315 to give a new Zn-porphyrin dye designated SM315-1. This specific modification of SM315 can effectively retard the interfacial charge recombination compared to that in YD2-o-C8 and WW-6 cells by reducing the contact between oxidized porphyrins and injected electrons in TiO2 substrate, and simultaneously improves the overall light harvesting ability of the co-sensitized film with the theoretical maximum limit of photocurrent to be 38.31 mA/cm2. The both favorable aspects suggest an attractive application of the fully novel Y123/SM315-1 co-sensitized film in dye-sensitized solar cell (DSSC).

Electronic structure, vibrational (FT-IR and FT-Raman), UV–Vis and NMR analysis of 5-(4-(2-(5-ethylpyridin-2-yl) ethoxy) benzyl) thiazolidine-2,4-dione by quantum chemical method

Abstract The vibrations of 5-(4-(2-(5-ethylpyridin-2-yl)ethoxy)benzyl) thiazolidine-2,4-dione(C19H20N2O3S) were investigated. The solid phase FTIR and FT-Raman spectra were recorded in the region 4000–400 cm−1 and 4000–50 cm−1 respectively. The vibrational frequencies of the title compound were obtained theoretically by DFT/B3LYP method with 6–31G(d,p) and 6–311G(d,p) basis sets for optimized geometry. The theoretically predicted FT-IR and FT-Raman spectra of the title molecule have been constructed. The detailed interpretation of the vibrational spectra has been carried out with aid of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology. UV–Vis spectrum of the title molecule was recorded and the electronic properties such as HOMO and LUMO energies were determined by Time-Dependent Density Functional Theory approach. The electrostatic potential surfaces, polarizability, NBO and thermodynamic properties of the title compound were discussed.

Excited-State Reactivity of [Mn(im)(CO)3 (phen)]+ : A Structural Exploration.

The electronic excited state reactivity of [Mn(im)(CO)3 (phen)]+ (phen = 1,10-phenanthroline; im = imidazole) ranging between 420 and 330 nm have been analyzed by means of relativistic spin-orbit time-dependent density functional theory and wavefunction approaches (state-average-complete-active-space self-consistent-field/multistate CAS second-order perturbation theory). Minimum energy conical intersection (MECI) structures and connecting pathways were explored using the artificial force induced reaction (AFIR) method. MECIs between the first and second singlet excited states (S1 /S2 -MECIs) were searched by the single-component AFIR (SC-AFIR) algorithm combined with the gradient projection type optimizer. The structural, electronic, and excited states properties of [Mn(im)(CO)3 (phen)]+ are compared to those of the Re(I) analogue [Re(im)(CO)3 (phen)]+ . The high density of excited states and the presence of low-lying metal-centered states that characterize the Mn complex add complexity to the photophysics and open various dissociative channels for both the CO and imidazole ligands. © 2018 Wiley Periodicals, Inc.

Solid-State Effects on the Optical Excitation of Push–Pull Molecular J-Aggregates by First-Principles Simulations

J-aggregates are a class of low-dimensional molecular crystals which display enhanced interaction with light. These systems show interesting optical properties as an intense and narrow red-shifted absorption peak (J-band) with respect to the spectrum of the corresponding monomer. The need to theoretically investigate optical excitations in J-aggregates is twofold: a thorough first-principles description is still missing and a renewed interest is rising recently in understanding the nature of the J-band, in particular regarding the collective mechanisms involved in its formation. In this work, we investigate the electronic and optical properties of a J-aggregate molecular crystal made of ordered arrangements of organic push–pull chromophores. By using a time-dependent density functional theory approach, we assess the role of the molecular packing in the enhancement and red shift of the J-band along with the effects of confinement in the optical absorption, when moving from bulk to low-dimensional crystal structures. We simulate the optical absorption of different configurations (i.e., monomer, dimers, a polymer chain, and a monolayer sheet) extracted from the bulk crystal. By analyzing the induced charge density associated with the J-band, we conclude that it is a longitudinal excitation, delocalized along parallel linear chains and that its overall red shift results from competing coupling mechanisms, some giving red shift and others giving blue shift, which derive from both coupling between transition densities and renormalization of the single-particle energy levels.

Density Functional Theory Investigation on Boron Subphthalocyanine-Ferrocene Dyads.

Twelve dyad structures were investigated using time-dependent density functional theory (TD-DFT). The dyads are all functionalized boron subphthalocyanines (SubPcs), where the SubPc unit acts as an acceptor, and ferrocene was chosen as the donor. Both axial and peripheral functionalization was investigated using four different linker groups between the SubPc unit and the ferrocene unit. The calculated molecular orbitals were compared for the 12 structures and discussed in the context of possible electron transport through the system and the use in organic photovoltaics. Optical properties of the 12 structures were investigated using a TD-DFT approach with the generalized gradient approximation type exchange correlation functional BP86 and using the Pople style basis set 6-31++G(d,p). Both changes in absorption properties by changing the linker group and changes in absorption properties when changing the position of the linker group were considered.

First-principles study of efficient phenothiazine-based D–π–A organic sensitizers with various spacers for DSSCs

Design of highly efficient sensitizers is one of the most significant issues for dye-sensitized solar cells (DSSCs). In this work, we designed and screened a series of phenothiazine-derivative dyes with donor–π spacer–acceptor (D–π–A) architecture based on a structural configuration with a phenothiazine group as the donor (D) part, a thiophene as the linker (π), and a 2-cyanoacrylic acid moiety (A) as the electron-acceptor segment, comparing the effects of different π-spacer groups between the electron donor and acceptor. The effects of different electron-deficient linker units on the absorption/emission spectra and photovoltaic properties were investigated by a combination of density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches. Based on the ground- and excited-state geometries, the absorption and emission spectra were calculated using the TD-DFT method. Different exchange–correlation functionals were first applied to establish a proper methodology for calculating the excited-state energy of the reference dye, known as TC104. The theoretical results calculated using the TD-CAM-B3LYP/B3LYP method with 6-311++G(d,p)/6-31G(d,p) basis set were found to agree well with the absorption and emission wavelengths for TC104 found experimentally. Overall, dye molecules SP1–SP4 (especially SP2 and SP4) were found to be promising sensitizers for highly efficient organic DSSCs.

Fine-tuning the photophysical properties of the five quinolin based nanophotoswitches in the gas phase, polar and nonpolar solvents: A TD-DFT approach

Fluorophores exhibiting excited state intramolecular proton transfer (ESIPT) have received increasing attention during the last decades. The swiftness of ESIPT process often avoids its inspection with only experimental methods, and theoretical explorations are often necessary to achieve a full justification of the observations and fine-tuning the ESIPT fluorescence properties. In this work, photo-switching in five novel red light emitting molecules 11hydroxy-indeno[1,2-b]quinolin-4ol (11HIQO), 4hydroxy-11H-indeno[1,2-b]quinolin-11one (4HIQO), 10H-indolo[3,2-b]quinolin-6-ol (10HIQO), benzofuro[3,2-b]quinolin-6-ol (BFQO) and benzothieno[3,2-b]quinolin-6-ol (BTQO) was comprehensively investigated using a robust protocol based on Time-Dependent Density Functional Theory (TD-DFT) at PBE0/6-311++G(2d,2p) level of theory. The interplay between π-conjugation and aromaticity was observed in all five photo-switching molecules in which are able to render both normal and keto fluorescence emissions with wavelengths longer than 610 nm and large Stokes shifts in gas phase (242–472 nm) and solvent media (187–385 nm). The normal and tautomer emissions were assigned to the relaxation of the initially excited Franck-Condon (FC) state to normal (S1-E) and tautomer (S1-K) states, respectively. The full photo-switching cycle and potential energy surfaces in the ground and excited states and structural parameters, H-bonding energy, absorption and emission wavelengths, vertical excitation and emission energies, oscillator strength, fluorescence rate constant, dipole moment, atomic charges and electron density at critical points for five new photochromic ESIPT switches were explored. The potential of these molecules as emissive switches in designing and generation of new displays and light sources in the molecular photo-devices were predicted based on their high red Stokes shifts.

Optical properties of β-brominated meso-tetraphenylporphyrins: Comparative experimental and computational studies

The UV-vis and fluorescence spectra of a series of [Formula: see text]-brominated derivatives of meso-tetraphenylporphyrin (H[Formula: see text]TPPBr[Formula: see text]; [Formula: see text] 0, 2, 4, 5, 6, 7, 8) were used to investigate the steroelectronic effects of bromine atoms on the optical properties of H[Formula: see text]TPP. The wavelength and intensity of the absorption and emission bands were found to be influenced by the bromine atoms. The degree of configuration interaction between the S[Formula: see text] and S[Formula: see text] excited states and fluorescence quantum yield and their dependence on the bromine atoms were also studied. Computational studies based on density functional theory and time-dependent density functional approach (DFT and TD-DFT) support and provide an explanation for the spectral changes associated with the bromination of H[Formula: see text]TPP. Furthermore, the solvent effect on the spectral properties of higher degrees of [Formula: see text]-bromination was attributed to the formation of relatively strong hydrogen bonds between their saddle-distorted porphyrin cores and the solvent molecules.

Photoexcitation in Solids: First-Principles Quantum Simulations by Real-Time TDDFT (Adv. Theory Simul. 8/2018)

Real-Time TDDFT Solid-state materials can exhibit highly nonlinear electronic and optical behaviors under laser excitation. However, a unified theoretical framework has not been established to explain the underlying mechanisms. In article number 1800055, Sheng Meng and co-workers develop an efficient real-time time-dependent density functional theory (TDDFT) approach for accurate simulations of excited state dynamics in solids. The photoexcitation process of the generation of hot electron-hole pairs under laser pulse illumination in a layered solid is shown schematically.

Highly-efficient sensitizer with zinc porphyrin as building block: Insights from DFT calculations

To further improve the photoelectronic conversion efficiency of dye-sensitized solar cell, a series of novel D-π-A dyes with Zn porphyrin as building block are evaluated with theoretical calculations. The effect of relative position of Zn-porphyrin (ZP) on the overall performance of D-π-A dye has been investigated by means of density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches. Through the analyzing the molecular geometry, electronic structure, transport properties and light harvesting and utilization of monomer dyes, dye-III is confirmed to be the most suitable one for DSSC application, due to its smaller HOMO-LUMO energy gap, broader absorption coverage, better transport capability, and larger short-circuit current density. Quantum dynamics simulation illustrates novel dyes constructed in current contribution are faster in electron transfer at dye@TiO2 interface. The overall efficiency of DSSC could be boosted if ZP unit was incorporated close to the acceptor group in D-π-A dye. Our work is expected to provide theoretical guideline for further designing and screening prospective sensitizers for DSSC.

Temperature-dependent UV absorption of biphenyl based on intra-molecular rotation investigated within a combined experimental and TD-DFT approach

ABSTRACTThe temperature dependence of the UV absorption spectra of biphenyl in solution is herein reported. The UV spectral shapes vary with an increase in temperature, where a decrease in intensity (hypochromism) and blue shifts are observed. The predicted UV spectra in the Time Dependent-Density Functional Theory (TD-DFT) framework within the B97D3 functional indicate a lowering of the biphenyl conjugation band and a blue shift of the spectra upon increasing the biphenyl twist dihedral angle.

Solvent-dependent inversion of circular dichroism signal in naproxen: An unusual effect!

The electronic circular dichroism (ECD) spectra of naproxen enantiomers were studied as a function of solvents using experimental (circular dichroism) and theoretical (time-dependent density functional theory) approaches. The (R)- and (S)-naproxen enantiomers presented an unusual inversion in their ECD signals in the presence of ethanol and water when compared with polar aprotic solvents such as acetonitrile. From a practical point of view, these findings deserve great attention because these solvents are widely used for high-performance liquid chromatography analysis in quality control of chiral pharmaceutical drugs. This is particularly relevant to naproxen because the (S)-naproxen has anti-inflammatory properties, whereas (R)-naproxen is hepatotoxic. A time-dependent density functional theory computer simulation was conducted to investigate the signal inversion using the solvation model based on density, a reparameterization of polarized continuum model. Electronic circular dichroism signals of conformers were calculated by computer simulation and their contribution to the combined spectra obtained according to Boltzmann weighting. It was found that the experimentally observed ECD signal inversion can be associated with the minor or major contribution of different conformers of naproxen.

Optical properties of plasmonic core-shell nanomatryoshkas: a quantum hydrodynamic analysis.

Plasmonic response of the metallic structure characterized by sub-nanometer dielectric gaps can be strongly affected by nonlocal or quantum effects. In this paper, we investigate these effects in spherical Na and Au nanomatryoshka structures with sub-nanometer core-shell separation. We use the state-of-the-art quantum hydrodynamic theory (QHT) to study both near-field and far-field optical properties of these systems: results are compared with the classical local response approximation (LRA), Thomas-Fermi hydrodynamic theory (TF-HT), and the reference time-dependent density functional theory (TD-DFT). We find that the results obtained using the QHT method are in a very good agreement with TD-DFT calculations, whereas other LRA and TF-HT significantly overestimate the field-enhancements. Thus, the QHT approach efficiently and accurately describes microscopic details of multiscale plasmonic systems whose sizes are computationally out-of-reach for a TD-DFT approach; here, we report results for Na and Au nanomatryoshka with a diameter of 60 nm.

Mechanism of Light Induced Radical Pair Formation in Coenzyme B12-Dependent Ethanolamine Ammonia-Lyase

Coenzyme B12 (adenosylcobalamin = AdoCbl)-dependent enzymes catalyze complex molecular transformations by employing radical chemistry. The initial step in the native catalytic cycle, upon substrate binding, involves homolytic cleavage of the Co–C bond of AdoCbl to form the Co(II)/Ado• radical pair (RP). Formation of Co(II)/Ado• is subsequently coupled with H atom abstraction from the substrate. Interestingly, these same RPs can be generated upon light absorption without presence of a substrate. Herein, the photochemistry associated with the mechanism of Co–C bond photocleavage inside the AdoCbl-dependent ethanolamine ammonia-lyase (EAL) was investigated using a combined time-dependent density functional theory and molecular mechanics (TD-DFT/MM) approach. Excited state potential energy surfaces (PESs), constructed as a function of axial bond lengths, were used to understand the photocleavage of the Co–C bond and to elucidate the mechanism of photodissociation for AdoCbl inside the enzyme. The S1 PES is ch...

A 2D covalent organic framework as a sensor for detecting formaldehyde.

Formaldehyde is the main cause of indoor pollution. In this research, we investigated the mechanism that the covalent organic framework (COF) identifies formaldehyde applying density functional theory (DFT) and time-dependent (TD) DFT approaches. On one hand, the calculation results of the geometric parameters, IR spectra, as well as 1H-NMR chemical shifts for protons that associated with the hydrogen bonding formation together with the electronic transition energies verified that the furcate hydrogen bonding formed between the COF and formaldehyde is enhanced in the excited S1 state and it is not beneficial to luminescence of the COF. On the other hand, excitingly, our further calculation results of the fluorescence rate coefficients also revealed that the strengthened hydrogen bonding behavior in S1 state caused an efficiently weakened luminescent phenomenon compared with that of the COF. Therefore, this analysis method, which qualitative collaborates with quantitative theoretically, demonstrates the possibility that the COF could be served as a sensor to detect formaldehyde. Graphical Abstract The luminescence of the Covalent Organic Framework can be greatly weakened after the addition of formaldehyde.

Design of novel phenanthrocarbazole dyes for efficient applications in dye-sensitized solar cells

Phenanthrocarbazole (PC)-based organic dye-sensitized solar cells (DSSCs) have been recently reported in experiments with an impressive high power conversion efficiency of over 12%. In this paper we report a computational study of the electronic structures, optical parameters and electron injection properties of a series of five PC dyes and the dye-TiO2 interfaces. Density functional theory (DFT) and time-dependent DFT (TDDFT) approaches were employed. We show that the incorporation of additional building blocks (indoline, carbazole, triphenylamine, or coumarin) to the PC donor moiety leads to obvious influence on the electronic structures and properties, compared to unitary electron donor PC dye. The binary electron-donor PC based dyes demonstrate better electronic properties and spectroscopic parameters. The calculated injection time of electrons from the excited state of dye to the conduction band of TiO2 is ideal for DSSC applications. The newly designed coumarin-PC and indoline-PC dyes show desirable energetic, electronic, and spectroscopic parameters for DSSCs. Our results are useful for a better understanding on the design rule of PC based organic dyes for future DSSCs.

Theoretical investigation of thiophene-linked porphyrin-perylene photosensitiser for bulk-heterojunction solar cells

In this work, quantum chemical calculations were applied to investigate a new series of porphyrin-perylene conjugates for their potential use as light-harvesting compounds in bulk-heterojunction solar cells. Molecular design relies on the integration of a electron-donating porphyrin and a electron-accepting perylene units via a spacer containing 0 to 10 thiophene rings. Electronic properties of these push–pull systems were studied using density functional theory (DFT) and time-dependent DFT approaches. Results show that introduction of thiophene-based spacer with different number of the thiophene rings significantly affects the electronic and absorption properties of the molecules. According to its suitable energy gap, efficient charge transfer and appropriate absorption behaviour determined by the calculation, the derivative having a terthiophene linker should be as the optimal compound among all molecules studied herein.

Valence and charge-transfer optical properties for some SinCm (m, n ≤ 12) clusters: Comparing TD-DFT, complete-basis-limit EOMCC, and benchmarks from spectroscopy.

Accurate optical characterization of the closo-Si12C12 molecule is important to guide experimental efforts toward the synthesis of nano-wires, cyclic nano-arrays, and related array structures, which are anticipated to be robust and efficient exciton materials for opto-electronic devices. Working toward calibrated methods for the description of closo-Si12C12 oligomers, various electronic structure approaches are evaluated for their ability to reproduce measured optical transitions of the SiC2, Si2Cn (n = 1-3), and Si3Cn (n = 1, 2) clusters reported earlier by Steglich and Maier [Astrophys. J. 801, 119 (2015)]. Complete-basis-limit equation-of-motion coupled-cluster (EOMCC) results are presented and a comparison is made between perturbative and renormalized non-iterative triples corrections. The effect of adding a renormalized correction for quadruples is also tested. Benchmark test sets derived from both measurement and high-level EOMCC calculations are then used to evaluate the performance of a variety of density functionals within the time-dependent density functional theory (TD-DFT) framework. The best-performing functionals are subsequently applied to predict valence TD-DFT excitation energies for the lowest-energy isomers of SinC and Sin-1C7-n (n = 4-6). TD-DFT approaches are then applied to the SinCn (n = 4-12) clusters and unique spectroscopic signatures of closo-Si12C12 are discussed. Finally, various long-range corrected density functionals, including those from the CAM-QTP family, are applied to a charge-transfer excitation in a cyclic (Si4C4)4 oligomer. Approaches for gauging the extent of charge-transfer character are also tested and EOMCC results are used to benchmark functionals and make recommendations.

FT-IR, UV–visible, and NMR Spectral Analyses, Molecular Structure, and Properties of Nevadensin Revealed by Density Functional Theory and Molecular Docking

ABSTRACTNevadensin 2-(4-methoxyphenyl)-5,7-dihydroxy-6,8-dimethoxy-4H-1-benzo-pyran-4-one] is a natural bioactive flavonoid compound that has the potential to become a novel “natural lead” in the field of drug discovery program. The molecular structure, vibrational frequencies, and corresponding vibrational assignment of nevadensin have been investigated experimentally and theoretically by employing the B3PW91/6–311++G(d,p) method. The fundamental vibrational wave numbers as well as their intensities were calculated, and a good correlation between experimental and scaled calculated wave numbers had been accomplished. The ultraviolet spectrum of the studied molecule was recorded in the region 200–500 nm, and the electronic properties were predicted by the time-dependent density functional theory approach. 1H and 13C NMR spectra have been calculated by employing the gauge-independent atomic orbital method. Nevadensin has been reported to exhibit antimicrobial activities against both Gram-positive and Gram-negative bacteria and also against the fungal pathogens, highlighting the pharmacological importance of the molecule.