Time-dependent Density Functional Theory Approach Research Articles

NB-Type Electronic Asymmetric Compounds as Potential Blue-Color TADF Emitters: Steric Hindrance, Substitution Effect, and Electronic Characteristics.

This article is devoted to the theoretical study of the effects of a connection pattern and stereo hindrance of different π-bridges, nitrogen-containing donors, and boron-containing acceptors on the electrooptic properties of NB-type electronic asymmetric compounds in conventional D−π–A frameworks by the density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches. By introducing three different connection groups (−O–, −CH2–, and −CMe2−) and guided by structural rationality, we formed 30 NB-type molecules, which have been classified into four types: D−π–A, D–X1−π–A, D−π–X1–A, and D–X1−π–X2–A (Xn are connection groups). Then, the energy gaps (ΔEST) between the first singlet and triplet excited states were evaluated by TD-LC-ωPBE with the optimal values of ω*, as well as an approximate method, which only considers the interaction between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). It is found that for the compounds with strong vibronic coupling, the calculated ΔEST defined as the difference of vertical excitation energies largely deviates from the experimental result. The consistency between the estimated and experimental values indicates that ΔEST is predominantly determined by the frontier molecular orbitals, which can be tuned by adjusting the modular overlap between HOMO and LUMO or the orientation of the donor and acceptor groups. Accompanied with the other electronic and optical properties, our study suggests that the interaction mode, D−π–X1–A, the modified D−π–A system with a rigidly fixed acceptor and a relatively free donor, can serve as a valuable molecular design pattern for new blue-colored thermally activated delayed fluorescence (TADF) emitters. Specifically, our calculations predict that ARD-BZN-2CMe2-PYN and its relatives might have excellent potential as TADF emitters.

Tunable excited-state intramolecular proton transfer reactions with N[sbnd]H or O[sbnd]H as a proton donor: A theoretical investigation

Excited-state intramolecular proton transfer (ESIPT) reactions occurring in the S1 state for five molecules, which possess five/six-membered ring intramolecular NH···N or OH···N hydrogen bonds bearing quinoline or 2-phenylpyridine moiety, have been described in detail by the time-dependent density functional theory (TD-DFT) approach using the B3LYP hybrid functional. For the five molecules, the constrained potential energy profiles along the ESIPT reactions show that proton transfer is barrierless in molecules possessing six-membered ring intramolecular H-bonds, which is smoother than that with certain barriers in five-membered ring H-bonding systems. For the latter, chemical modification by a more strong acid group can lower the ESIPT barrier significantly, which harnesses the ESIPT reaction from a difficult type to a fast one. The energy barrier of the ESIPT reaction depends on the intensity of the intramolecular H-bond, which can be measured with the topological descriptors by topology analysis of the bond critical point (BCP) of the intramolecular H-bond. It is found that when the value of electron density ρ(r) at BCP is bigger than 0.025a.u., the corresponding molecule might go through an ultrafast and barrierless ESIPT process, which opens a new scenario to explore the ESIPT reactions.

Molecular structure, vibrational spectra, NBO, Fukui function, HOMO-LUMO analysis and molecular docking study of 6-[(2-methylphenyl)sulfanyl]-5-propylpyrimidine-2,4(1H,3H)-dione

Theoretical and experimental FT-IR and FT-Raman vibrational spectral analysis of 6-[(2-methylphenyl)sulfanyl]-5-propylpyrimidine-2,4(1H,3H)-dione have been recorded in the region 4000-400 cm-1 and 4000-100 cm-1 insolid phase. The molecular geometrical parameters, bond length, bond angle and vibrational wave numbers, harmonic vibrational frequency were investigated using the density functional theory B3LYP method with the 6-311++G(d,p) basis set. The stability of the molecule has been investigated using the natural bond orbital (NBO) analysis. The electronic properties such as HOMO-LUMO energies were determined by the time-dependent DFT approach. The thermodynamical properties and the first order hyperpolarizability and molecular electrostatic potential (MEP) of the title compound were also studied. The electron density-based local reactivity descriptors such as the Fukui functions were calculated to explain the chemical selectivity or reactivity site in the molecule. The molecule orbital contributions were investigated using the total density of states (TDOS), the sum of 𝛼 and 𝛽 electron density of states (𝛼𝛽DOS). The molecular docking (ligand-protein) simulations have been performed using the SWISSDOCK server. The full fitness (FF) score and hydrogen bonding interaction and binding affinity values revealed that title compound can act as potential inhibitor against HIV-1 protease.

The effect of relative position of the π-spacer center between donor and acceptor on the overall performance of D-π-A dye: a theoretical study with organic dye

The influence of the relative position of π-spacer center between donor and acceptor on the dye-sensitized solar cell (DSSC) performance is expounded by analyzing the geometry, electronic structure, optical absorption property, and intramolecular charge transfer, as well as reorganization energy by means of density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches. The results based on electronic structure and absorption property indicate that the dyes with introduction of building blocks to p1 position will generate more efficient charge separated states and present red-shifted in spectra. According to the analysis of intramolecular charge transfer, the results show that although introducing building blocks to p1 position can not make all structures to reduce orbital overlap, all the dyes with relatively small distance between donor and π-spacer center can enhance the amount of qCT and DCT. Additionally, the dyes with building blocks are introduced to p1 position that give better charge transfer balance performance due to their smaller Λh and Λe values. That is to say, the dye with a rigidified-aromatic as π-spacer, properly adjusting the position of π-spacer center is a valid approach for achieving great performance of DSSC.

Structural, spectral analysis of ambroxol using DFT methods

The FT-IR and FT-Raman spectra of Ambroxol are recorded in the region 4000–450 cm−1 and 4000–50 cm−1 respectively. Theoretical calculations were performed by density functional theory (DFT) method using 6-31G(2d,3p) basis set. The complete vibrational assignments of wavenumbers were made on the basis of potential energy distribution (PED). The results of the calculations were applied to the simulated spectra of the title compound, which show excellent agreement with the observed spectra. The frontier orbital energy gap and dipole moment, illustrates the high reactivity of the title molecule. Stability of the molecule arising from hyperconjugative interactions and charge delocalization has been analysed using natural bond orbital (NBO) analysis. Molecular electrostatic potential (MEP), the electronic properties were performed by time-dependent DFT (TD-DFT) approach, and HOMO–LUMO energy levels are also constructed.

Multiphoton ionization of many-electron atoms and highly-charged ions in intense laser fields: a relativistic time-dependent density functional theory approach

We develop an efficient numerical implementation of the relativistic time-dependent density functional theory (RTDDFT) to study multielectron highly-charged ions subject to intense linearly-polarized laser fields. The interaction with the electromagnetic field is described within the electric dipole approximation. The resulting time-dependent relativistic Kohn–Sham (RKS) equations possess an axial symmetry and are solved accurately and efficiently with the help of the time-dependent generalized pseudospectral method. As a case study, we calculate multiphoton ionization probabilities of the neutral argon atom and argon-like xenon ion. Relativistic effects are assessed by comparison of our present results with existing non-relativistic data.

Theoretical insights into the ultrafast excited-state intramolecular proton transfer (ESIPT) mechanism in a series of amide-based N[sbnd]H⋯N hydrogen-bonding compounds

Excited-state intramolecular proton transfer (ESIPT) has many important potential applications. In this paper, the geometries of a series of amide-based NH⋯N hydrogen-bonding compounds in their ground S0 states and first excited singlet S1 states were optimized with density functional theory (DFT) and time-dependent density functional theory (TD-DFT) approaches. Both topological analysis and noncovalent interactions analysis show strong intramolecular hydrogen-bonds in the studied five systems and the electron density function ρ(r) exhibits good linear relationship with the distance of H⋯N2. The potential energy curves of the S0 and S1 states were scanned by using of DFT and TD-DFT to elucidate the ESIPT process. It reveals that all the systems considered here can undergo an ultrafast ESIPT reaction, with energy barrier of less than 0.05 eV, giving rise to the single fluorescence emission from the proton-transfer tautomer. It is also found that the shorter the hydrogen bond in the normal-form S1 state, the easier the ESIPT takes place.

Fine-tuning π-spacer for high efficiency performance DSSC: A theoretical exploration with [formula omitted] based organic dye

Based on density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches, a series of triphenylamine based organic dyes that modified by electron-withdrawing (EW) or electron-deficient (ED) substituent groups are investigated. The properties of all the isolated dyes, including frontier molecular orbital, intramolecular charge transfer, absorption spectra, maximal photon generated current (Jph) and intermolecular interaction between dye and I2 are investigated theoretically to confirm which dyes can produce great performance for dye-sensitized solar cell (DSSC). Subsequently, the structures of dye combined with (TiO2)64 cluster are optimized by means of Vienna ab initio simulation package (VASP) code. Then the interfacial interaction between the dye and semiconductor is further discussed to reveal the interfacial charge injection process by means of interfacial electron transfer code. The importance of fine-tuning π-spacer is also demonstrated by the density of state (DOS) plot and photo-induced charge transfer dynamics. Compared with other dyes, TA-CN dye shows outstanding performance because of the strong coupling of the absorbed dye's orbitals with substrate orbitals and the fast as well as complete charge injection process. The purpose of our study is expected to provide a promising way to design possible candidate sensitizers for DSSC.

Physical and optical properties of DCJTB dye for OLED display applications: Experimental and theoretical investigation

In this study, 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidin-4-yl-vinyl)-4H-pyran (DCJTB) was achieved using the experimental and theoretical studies. The electronic, optical and spectroscopic properties of DCJTB molecule were first investigated by performing experimental both solution and thin film techniques and then theoretical calculations. Theoretical results showed that one intense electronic transition is 505.26 nm a quite reasonable and agreement with the measured experimental data 505.00 and 503 nm with solution technique and film technique, respectively. Experimental and simple models were also taken into consideration to calculate the optical refractive index (n) of DCJTB molecule. The structural and electronic properties were next calculated using density functional theory (DFT) with B3LYP/6-311G (d, p) basis set. UV, FT-IR spectra characteristics and the electronic properties, such as frontier orbitals, and band gap energy (Eg) of DCJTB were also recorded time-dependent (TD) DFT approach. The theoretical Eg value were found to be 2.269 eV which is consistent with experimental results obtained from solution technique for THF solvent (2.155 eV) and literature (2.16 eV). The results herein obtained reveal that solution is simple, cost-efficient and safe for optoelectronic applications when compared with film technique.

Theoretical insights into the excited-state intramolecular proton transfer (ESIPT) mechanism in a series of amino-type hydrogen-bonding dye molecules bearing the 10-aminobenzo[h]quinoline chromophore

Structures of a series of 10-aminobenzo[h]quinoline (ABQ) derivatives in their ground states and first excited singlet states were optimized with density functional theory (DFT) and time-dependent density functional theory (TD-DFT) approaches. Their electronic absorption spectra and fluorescence emission spectra were simulated on the basis of the calculations on the vertical excitation and emission energies, which agree very well with the corresponding experimental spectra. The potential energy curves of their ground state and first excited singlet state were calculated by TD-DFT to elucidate the mechanisms of the excited-state intramolecular proton transfer (ESIPT) processes. It reveals that all the systems considered here can undergo a fast or even ultrafast ESIPT reaction, giving rise to the single fluorescence emission from their tautomer forms, as observed experimentally.

Excitons in Solids from Time-Dependent Density-Functional Theory: Assessing the Tamm-Dancoff Approximation

Excitonic effects in solids can be calculated using the Bethe-Salpeter equation (BSE) or the Casida equation of time-dependent density-functional theory (TDDFT). In both methods, the Tamm-Dancoff approximation (TDA), which decouples excitations and de-excitations, is widely used to reduce computational cost. Here, we study the effect of the TDA on exciton binding energies of solids obtained from the Casida equation using long-range-corrected (LRC) exchange-correlation kernels. We find that the TDA underestimates TDDFT-LRC exciton binding energies of semiconductors slightly, but those of insulators significantly (i.e., by more than 100%), and thus it is essential to solve the full Casida equation to describe strongly bound excitons. These findings are relevant in the ongoing search for accurate and efficient TDDFT approaches for excitons.

Tuning the Spectroscopic Properties of Ratiometric Fluorescent Metal Indicators: Experimental and Computational Studies on Mag-fura-2 and Analogues.

In this joint theoretical and experimental work, we investigate the properties of Mag-fura-2 and seven structurally related fluorescent sensors designed for the ratiometric detection of Mg2+ cations. The synthesis of three new compounds is described, and the absorption and emission spectra of all of the sensors in both their free and metal-bound forms are reported. A time-dependent density functional theory approach accounting for hydration effects using a hybrid implicit/explicit model is employed to calculate the absorption and fluorescence emission wavelengths, study the origins of the hypsochromic shift caused by metal binding for all of the sensors in this family, and investigate the auxochromic effects of various modifications of the "fura" core. The metal-free forms of the sensors are shown to undergo a strong intramolecular charge transfer upon light absorption, which is largely suppressed by metal complexation, resulting in predominantly locally excited states upon excitation of the metal complexes. Our computational protocol might aid in the design of new generations of fluorescent sensors with low-energy excitation and enhanced properties for ratiometric imaging of metal cations in biological samples.

Spectroscopic and theoretical studies of 2-acetylbenzo[b]selenophen-3(2H)-one

In the present study, the FT-IR spectrum of 2-acetylbenzo[b]selenophen-3(2H)-one (2ACSeP, C10H8O2Se) has been recorded in the range of 4000–400 cm−1. The molecular structure of 2ACSeP in the ground state has been investigated by the density functional method (B3PW91) with 6-31G(d,p), 6-311G(d,p), 6-311G(2df,p) and 6-311G(3df,3pd) basis sets. From the potential energy surface calculation, there are two conformers, s-cis and s-trans for this molecule. The computational results diagnose the most stable conformer of 2ACSeP as the s-trans form. Making use of the recorded data, the complete vibrational assignments are made and analysis of the observed fundamental bands of molecule is carried out. The complete assignments are performed on the basis of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMF). The molecular stability and bond strength were investigated by applying the natural bond orbital analysis (NBO) and natural localized molecular orbital (NLMO) analysis. The electronic properties, such as excitation energies, absorption wavelength, HOMO and LUMO energies were performed by the time dependent DFT (TD-DFT) approach. The 1H and 13C nuclear magnetic resonance chemical shifts of the molecule were calculated using the gauge-including atomic orbital (GIAO) method and compared with experimental results.

The effect of D–[De–π–A]n (n = 1, 2, 3) type dyes on the overall performance of DSSCs: a theoretical investigation

A series of D–[De–π–A]n (n = 1, 2, 3) organic dyes have been theoretically investigated by means of density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches.

Investigating the optical properties of BOIMPY dyes using ab initio tools.

Using a computational approach combining Time-Dependent Density Functional Theory (TD-DFT) and second-order Coupled Cluster (CC2) approaches, we investigate the spectral properties of a large panel of BOIMPY dyes. BOIMPY derivatives constitute a new class of fluorophores that appeared only very recently [Angew. Chem. Int. Ed., 2016, 55, 13340-13344] and display intriguing properties. First, we show that theory is able to reproduce experimental 0-0 energies with reasonable accuracy, and more importantly excellent consistency (R = 0.99). Next, by analyzing the nature of the excited-states, we show that the first electronic transition does not imply a significant charge-transfer character and significantly differs from the one of the parent BODIPYs. Third, we unravel the vibrational modes responsible for the specific band shapes of the BOIMPY derivatives. Finally, using theory to design new compounds, we propose substitution patterns leading to redshifted absorption spectra, up to ca. 1000 nm.

Preparation and Photophysical Properties of All-trans Acceptor–π-Donor (Acceptor) Compounds Possessing Obvious Solvatochromic Effects

A series of all-trans acceptor–π-donor (acceptor) compounds (BAQ, SFQ, BLQ, and XJQ) were conveniently synthesised and characterised by infrared, nuclear magnetic resonance, mass spectrometry, and elemental analysis. Their photophysical properties, including linear absorption, one-photon excited fluorescence, two-photon absorption, and two-photon excited fluorescence, were systematically investigated. All the compounds show obvious solvatochromic effects, such as significant bathochromic shifts of the emission spectra and larger Stokes shifts in more polar solvents. Under excitation from a femtosecond Ti : sapphire laser with a pulse width of 140 fs, they all exhibit strong two-photon excited fluorescence, and the two-photon absorption cross-sections in THF are 851 (BAQ), 216 (SFQ), 561 (BLQ), and 447 (XJQ) GM respectively. A combination of density functional theory (DFT) and time-dependent density functional theory (TDDFT) approaches was used to investigate the relationships between the structures and the photophysical properties of these compounds. The results show that they may have a potential application as polarity-sensitive two-photon fluorescent probes.

Theoretical insight into the excited-state intramolecular proton transfer mechanisms of three amino-type hydrogen-bonding molecules

Excited-state intramolecular proton transfer (ESIPT) dynamics of the amino-type hydrogen-bonding compound 2-(2′-aminophenyl)benzothiazole (PBT-NH2) as well as its two derivatives 2-(5′-cyano-2′-aminophenyl)benzothiazole (CN-PBT-NH2) and 2-(5′-cyano-2′-tosylaminophenyl)benzothiazole (CN-PBT-NHTs) were studied by the time-dependent density functional theory (TD-DFT) approach with the B3LYP density functional, and their absorption and emission spectra were also explored at the same level of theory. A good agreement is observed between the theoretical simulations and experimental spectra, indicating that the present calculations are reasonably reliable. In addition, it is also found that the energy barriers of the first excited singlet state of the three targeted molecules along the ESIPT reaction are computed to be 0.38, 0.34 and 0.12eV, respectively, showing the trend of gradual decrease, which implies that the introduction of the electron-withdrawing cyano or tosyl group can facilitate the occurrence of the ESIPT reaction of these amino-type H-bonding systems. Following the ESIPT, both CN-PBT-NH2 and CN-PBT-NHTs dye molecules can undergo the cis-trans isomerization reactions in the ground-state and excited-state potential energy curves along the C2-C3 bond between benzothiazole and phenyl moieties, where the energy barriers of the trans-tautomer→cis-tautomer isomerizations in the ground states are calculated to be 0.83 and 0.34eV, respectively. According to our calculations, it is plausible that there may exist the long-lived trans-tautomer species in the ground states of CN-PBT-NH2 and CN-PBT-NHTs.

Computational study of modification of cyanidin as high efficient organic sensitizer for dye sensitized solar cells

We report results of computational study of a newly designed cyanidin based molecular structure, P02, as efficient sensitizers for dye sensitized solar cells (DSSCs). To design this P02, widely used promising natural dye sensitizer cyanidin [1] is combined with α-cyanocinnamic acid and the resultant structure is computationally simulated by using SPARTAN’10 software package [2].The moleculer geometries, electronic structures, absorption spectra and deprotonation enengies of newely designed organic sensitizer are investigated through density functional theory(DFT) and time-dependent density functional theory(TDDFT) approach using GAUSSIAN’09W software package [3]. Furthermore DFT and TDDFT computational calculations are performed on cyanadin too, as reference. The solvation effect in ethanol are included in all calculations.The computational studies on the new dye have shown broadening of the absorption spectra in visible region with significant shifting towards a longer wavelength compared to the cyanidin. Our computational study results indicated that the new dye P02 should exhibit better performance as a sensitizer due to its improved optical properties.

DFT and TD-DFT calculation of new thienopyrazine-based small molecules for organic solar cells.

BackgroundNovel six organic donor-π-acceptor molecules (D-π-A) used for Bulk Heterojunction organic solar cells (BHJ), based on thienopyrazine were studied by density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches, to shed light on how the π-conjugation order influence the performance of the solar cells. The electron acceptor group was 2-cyanoacrylic for all compounds, whereas the electron donor unit was varied and the influence was investigated.MethodsThe TD-DFT method, combined with a hybrid exchange-correlation functional using the Coulomb-attenuating method (CAM-B3LYP) in conjunction with a polarizable continuum model of salvation (PCM) together with a 6-31G(d,p) basis set, was used to predict the excitation energies, the absorption and the emission spectra of all molecules.ResultsThe trend of the calculated HOMO–LUMO gaps nicely compares with the spectral data. In addition, the estimated values of the open-circuit photovoltage (Voc) for these compounds were presented in two cases/PC60BM and/PC71BM.ConclusionThe study of structural, electronics and optical properties for these compounds could help to design more efficient functional photovoltaic organic materials.

Disentangling the Photophysics of DNA-Stabilized Silver Nanocluster Emitters

It has been already established that DNA–silver fluorophores present two intense absorption bands, one in the visible and the other in the UV spectral region, and that the excitation of both bands produces a common fluorescence signal. Nevertheless, the detailed mechanism responsible for this coupling is still elusive. In this context, our work is a significant leap forward in this goal by providing a dynamic picture of the excitation and the processes that take place upon light absorption in these systems using a time-dependent density functional tight-binding approach. In the present work, we explore the electronic coupling mechanism in a cluster composed of a double string of deoxypolycytosine with six bases and a rod of six Ag atoms.