Time-dependent Density Functional Theory Research Articles

High harmonic generation in organic molecules: a time-dependent density functional theory (TDDFT) approach

High harmonic generation in organic molecules: a time-dependent density functional theory (TDDFT) approach

Elaborating H-bonding effect and excited state intramolecular proton transfer of 2-(2-hydroxyphenyl)benzothiazole based D-π-A fluorescent dye.

2-(2-Hydroxyphenyl)benzothiazole (HBT) derivatives with donor-π-acceptor (D-π-A) structure have received extensive attention as a class of excited state intramolecular proton transfer (ESIPT) compounds in the fields of biochemistry and photochemistry. The effects of electron-donors (triphenylamine and anthracenyl), the position of substituents and solvent polarity on the fluorescence properties and ESIPT mechanisms of HBT derivatives were investigated through time-dependent density functional theory (TDDFT) calculations. Potential energy curves (PECs) and frontier molecular orbitals (FMOs) reveal that the introduction of the triphenylamine group on the benzene ring enhances intramolecular HB, thereby benefiting the ESIPT process. Analysis of their spectra reveals that P-TPA (para position for TPA) and M-TPA (meta position for TPA) are both excellent candidates for fluorescent dyes because of their large Stokes shifts. The PECs of four derivatives indicate that the ESIPT process of P-TPA in dimethyl sulfoxide (DMSO) solvent is the most likely to occur. The research revealed that both P-TPA and P-En (para positions for both TPA and En) can undergo a spontaneous transformation from the enol to the keto form in the S1 state. Furthermore, the ESIPT process was found to be enhanced with an increase in polarity. The energy barrier of P-TPA(N*) → P-TPA(K*) is 3.06 kcal mol-1 in the S1 state and its reversed energy barrier is 4.47 kcal mol-1. The para triphenylamine group could accelerate the ESIPT reactions, as it has a greater impact on the excited state intramolecular hydrogen bond (ESIHB) compared to meta-substitution of the triphenylamine group.

Chemical Constituents of the Deep-Sea-Derived Penicillium citrinum W22 and Their Ferroptosis Inhibitory Activity.

One new monomeric citrinin analog (1) and 42 known compounds (2-43) were isolated from Penicillium citrinum W22. The structure of 1 was determined by detailed analysis of the 1D and 2D nuclear magnetic resonance (NMR), HRESIMS, and time-dependent density functional theory (TD-DFT)-based electronic circular dichroism (ECD) calculation. Penicitrinol A (2) and methyl 2-(2-acetyl-3,5-dihydroxy-4,6-dimethylphenyl) acetate (11) significantly inhibited renin-angiotensin system-selective lethal 3 (RSL3)-induced ferroptosis with half maximal effective concentration (EC50) values of 1.6 and 34.0µM, respectively.

Exploring DL-2-aminobutyric acid: DFT analysis and spectroscopic characterization

DL-2-aminobutyric acid (α-aminobutyric acid), an alpha amino acid, has been extensively investigated through experimental and theoretical methods. Theoretical analyses have been carried out using density functional theory. Spectroscopic techniques such as Fourier transform infrared and UV spectroscopy have been employed, with experimental spectra aligning closely with theoretical predictions. Studies of electronic transitions between unoccupied and occupied states have been performed in solvents like dimethyl sulfoxide (DMSO) and Methanol (MeOH). The Time Dependent Density Functional Theory (TD-DFT) method and Iterative Electrostatic Potential Continuum Model (IEPCM) model assessed charge transfer in these solvents. Vibrational analysis and other studies, including Frontier Molecular Orbital (FMO), natural bond analysis, and non-linear optical analysis, were based on structures optimized using the B3LYP method with the 6-311++G(d,p) basis set. Total potential energy distribution analysis has been done for the detailed analysis of internal coordinates to each vibrational mode. The atom in molecule theory was applied via electron localization functions to examine ellipticity, binding energy, and isosurface projections. Natural bond analysis was conducted to investigate interference energy, bond hybridization, and interactions between donor and acceptor sites. Reactive sites were identified through Fukui functions and molecular electrostatic potential analysis. Thermodynamic properties, including free energy, enthalpy, entropy, internal energy, and heat capacities at various temperatures, were computed using the Atomistica online calculator. The electrophilicity index, derived from FMO analysis, suggested the compound’s potential bioactivity. Molecular docking studies with various proteins revealed the lowest binding energy of −4.9 kcal/mol. α-Aminobutyric acid and its derivatives exhibit similar Absorption, distribution, metabolism, and excretion (ADME) properties, indicating their potential utility in drug development. Minimal conformational changes in the peptide backbone after equilibrium have been explained by using molecular dynamics simulations, and molecular mechanics Poisson–Boltzmann surface area calculation showed an average free binding energy of −23.48 ± 1.72 kcal/mol.

Excited-State Rotational Dynamics of Amine-Functionalized Terephthalic Acid Derivatives as Linker Models for Metal-Organic Frameworks.

Understanding how structural modifications affect the photophysics of organic linkers is crucial for their integration into metal-organic frameworks (MOFs) for light-driven applications. This study explores the impact of varying the amine functional group position on two terephthalic acid derivatives─linker 1 and linker 2─by investigating their photophysics through a combination of steady-state and ultrafast laser spectroscopy and time-dependent density functional theory (TD-DFT) calculations. With tetrahydrofuran as the solvent, time-correlated single-photon counting revealed a 2-fold increase in the S1 excited-state lifetime of the molecule with the amine group at the meta position compared with that of the molecule with the amine group at the ortho position. This phenomenon can be attributed to restricted intramolecular twisting for the molecule with the amine group in the meta position. In this regime, an interplay of high-energy steric and conjugation barriers was revealed for the molecule with the amine group at the meta position by TD-DFT calculations. Moreover, femtosecond/nanosecond transient absorption spectroscopy revealed a reversible excited-state conformational change for the ortho isomer via intramolecular rotation that occurred within ∼110 ps, unlocking a triplet state manifold. This study underscores the importance of modifying organic emitters, either as free linkers or within MOFs, to increase their performance in sensing and light-emitting applications.

Deciphering the Photophysical Properties of Nonplanar Heterocyclic Compounds in Different Polarity Environments.

Nonplanar (butterfly-shaped) phenothiazine (PTZ) and its derivative's (M-PTZ) photophysical and spectral properties have been tuned by varying the solvents and their polarity and investigated employing spectroscopic techniques such as UV-Vis, steady-state and time-resolved fluorescence, and TDDFT calculations. The UV-Vis absorption studies and TDDFT calculations reveal two distinct bands for both compounds: a strong π-π* transition at shorter wavelengths and a weaker n-π* transition, which displays a little bathochromic shift in polar solvents. The detailed emission studies reveal that such dual emission is a result of the photoinduced excited-state conjugation enhancement (ESCE) process. The band at a shorter wavelength corresponds to the locally excited (LE) state, while the longer wavelength band arises from the planarized excited state resulting from ESCE. With the increase in solvent polarity, the LE band is less affected, whereas strong positive solvatochromism is observed for the ESCE band. As the solvent polarity increases, the ESCE band demonstrates significant positive solvatochromism, while emission intensity decreases with higher solvent polarity, suggesting stabilization of the excited state. The biexponential decay of fluorescence lifetimes further corroborates the dual emission behavior of PTZ and M-PTZ. PTZ exhibits a higher photoluminescence quantum yield (PLQY) than that observed for M-PTZ, and the solvent viscosity influences the PLQY, indicating that nonradiative decay is activated during the planarization of the excited state, also known as excited-state conjugation enhancement. Furthermore, the (time-dependent) density functional theory (TD) DFT calculations performed to understand the geometrical parameters and the electronic transitions of these model molecules further corroborate experimental findings. These findings underscore the significant influence of solvent polarity and molecular structure on the dual emission and excited-state dynamics of PTZ and M-PTZ, which eventually hold substantial implications for advanced photophysical applications.

A Cost-Effective Computational Strategy for the Electronic Layout Characterization of a Second Generation Light-Driven Molecular Rotary Motor in Solution.

Light-driven molecular rotary motors are nanometric machines able to convert light into unidirectional motions. Several types of molecular motors have been developed to better respond to light stimuli, opening new avenues for developing smart materials ranging from nanomedicine to robotics. They have great importance in the scientific research across various disciplines, but a detailed comprehension of the underlying ultrafast photophysics immediately after photo-excitation, that is, Franck-Condon region characterization, is not fully achieved yet. For this aim, it is first required to rely on an accurate description at ab initio level of the system in this potential energy region before performing any further step, that is, dynamics. Thus, we present an extensive investigation aimed at accurately describing the electronic structure of low-lying electronic states (electronic layout) of a molecular rotor in the Franck-Condon region, belonging to the class of overcrowded alkenes: 9-(2-methyl-2,3-dihydro-1H-cyclopenta[a]naphthalen-1-ylidene)-9H-fluorene. This system was chosen since its photophysics is very interesting for a more general understanding of similar compounds used as molecular rotors, where low-lying electronic states can be found (whose energetic interplay is crucial in the dynamics) and where the presence of different substituents can tune the HOMO-LUMO gap. For this scope, we employed different theory levels within the time-dependent density functional theory framework, presenting also a careful comparison adopting very accurate post Hartree-Fock methods and characterizing also the different conformations involved in the photocycle. Effects on the electronic layout of different functionals, basis sets, environment descriptions, and the role of the dispersion correction were all analyzed in detail. In particular, a careful treatment of the solvent effects was here considered in depth, showing how the implicit solvent description can be accurate for excited states in the Franck-Condon region by testing both linear-response and state-specific formalisms. As main results, we chose two cost-effective (accurate but relatively cheap) theory levels for the ground and excited state descriptions, and we also verified how choosing these different levels of theory can influence the curvature of the potential via a frequency analysis of the normal modes of vibrations active in the Raman spectrum. This theoretical survey is a crucial step towards a feasible characterization of the early stage of excited states in solution during photoisomerization processes wherein multiple electronic states might be populated upon the light radiation, leading to a future molecular-level interpretation of time-resolved spectroscopies.

A computational study on the effect of structural isomerism on the excited state lifetime and redox energetics of archetype iridium photoredox catalyst platforms [Ir(ppy)2(bpy)]+ and Ir(ppy)3.

This study investigates the impact of structural isomerism on the excited state lifetime and redox energetics of heteroleptic [Ir(ppy)2(bpy)]+ and homoleptic Ir(ppy)3 photoredox catalysts using ground-state and time-dependent density functional theory methods. While the ground- and excited-state reduction potentials differ only slightly among the isomers of these complexes, our findings reveal significant variations in the radiative and non-radiative decay rates of the reactivity-controlling triplet 3MLCT states of these closely related species. The observed differences in radiative decay rates could be traced back to variations in the transition dipole moment, vertical energy gaps, and spin-orbit coupling of the isomers. In [Ir(ppy)2(bpy)]+, transition dipole moment differences play a significant role in controlling the relative lifetime of the triplet states, which we rationalized by a vectorial analysis of permanent dipole moments of the ground and excited states. Regarding the two isomers of Ir(ppy)3, changes in radiative decay rates were primarily attributed to variations in vertical energy gaps and intensity borrowing from other singlet-singlet transitions driven by spin-orbit coupling. Non-radiative decay variations were assessed in terms of differences in reorganization energies, adiabatic energy gap, and spin-orbit coupling. For both complexes, reorganization energies associated with low-energy molecular vibrations and metal-ligand bond length changes following the de-excitation process were major contributors. These insights provide a deeper understanding of how molecular design can be leveraged to optimize the performance of iridium-based photoredox catalysts, potentially guiding the development of more efficient catalytic systems for future applications.

Benchmark computations of nearly degenerate singlet and triplet states of N-heterocyclic chromophores. II. Density-based methods.

In this paper, we demonstrate the performance of several density-based methods in predicting the inversion of S1 and T1 states of a few N-heterocyclic triangulene based fused ring molecules (popularly known as INVEST molecules) with an eye to identify a well performing but cost-effective preliminary screening method. Both conventional linear-response time-dependent density functional theory (LR-TDDFT) and ΔSCF methods (namely maximum overlap method, square-gradient minimization method, and restricted open-shell Kohn-Sham) are considered for excited state computations using exchange-correlation (XC) functionals from different rungs of Jacob's ladder. A well-justified systematism is observed in the performance of the functionals when compared against fully internally contracted multireference configuration interaction singles and doubles and/or equation of motion coupled-cluster singles and doubles (EOM-CCSD), with the most important feature being the capture of spin-polarization in the presence of correlation. A set of functionals with the least mean absolute error is proposed for both the approaches, LR-TDDFT and ΔSCF, which can be more cost-effective alternatives for computations on synthesizable larger derivatives of the templates studied here. We have based our findings on extensive studies of three cyclazine-based molecular templates, with additional studies on a set of six related templates. Previous benchmark studies for subsets of the functionals were conducted against the domain-based local pair natural orbital-similarity transformed EOM-CCSD (STEOM-CCSD), which resulted in an inadequate evaluation due to deficiencies in the benchmark theory. The role of exact-exchange, spin-contamination, and spin-polarization in the context of DFT comes to the forefront in our studies and supports the numerical evaluation of XC functionals for these applications. Suitable connections are drawn to two and three state exciton models, which identify the minimal physics governing the interactions in these molecules.

Exploring the impact of substituents on the photophysical properties of boron dipyrromethene dyes for enhanced photovoltaic performance

Abstract Boron dipyrromethene (BODIPY) dyes are known for their strong fluorescence and excellent photostability, making them vital for various photoelectric applications. This study explores how different substituents affect the photophysical properties of BODIPY dyes to improve their performance in dye-sensitized solar cells (DSSCs). We examine six distinct BODIPY dye structures with unique electron-withdrawing (NO₂, CHO, Br) and electron-donating (OCH₃, NPh₂) substituents, along with a hydrogen-substituted variant, and report key photovoltaic parameters, including open-circuit voltage (Vₒc), short-circuit current density (Jₛc), fill factor (FF), and energy conversion efficiency (Ω). Using density functional theory (DFT) and time-dependent DFT (TD-DFT), we analyze the dyes' light-harvesting efficiency, electron injection efficiency, and overall energy conversion efficiency. Our results indicate that electron-donating groups, especially NPh₂ and OCH₃, significantly enhance Voc, Jsc, FF, and Ω, leading to improved energy conversion efficiencies. In contrast, while electron-withdrawing substituents increase chemical stability, they typically result in lower photovoltaic performance. This research underscores the importance of strategic substituent selection in optimizing BODIPY dyes for enhanced photoelectric performance, offering valuable insights for designing efficient photovoltaic materials.

Simulations of Attosecond Metallization in Quartz and Diamond Probed with Inner-Shell Transient Absorption Spectroscopy.

When dielectrics are hit with intense infrared (IR) laser pulses, transient metalization can occur. The initial attosecond dynamics behind this metallization are not entirely understood. Therefore, simulations are needed to understand this process and to help interpret experimental observations of it, such as with attosecond transient absorption (ATA). In this paper, we present first-principles simulations of ATA based on bulk-mimicking clusters and real-time time-dependent density functional theory (RT-TDDFT), with Koopmans-tuned range-separated hybrid functionals and Gaussian basis sets. Our method gives good agreement with the experiment for the breakdown threshold in silica and diamond. This breakdown voltage corresponds to a Keldysh parameter of approximately one and thus involves a transition to a regime where the dynamics are driven by tunneling. Pumping at an amplitude just below this value causes a mixture of multiphoton and tunneling excitations across the band gap to occur. The computed extreme ultraviolet and X-ray attosecond transient spectra also agree well with the experiment and show a decrease in optical density due to the transient population of the conduction band from the IR field. First-principles approaches such as this are valuable for interpreting the complicated modulations in a spectrum and for guiding future attosecond experiments on solids.

PH- and Saccharide-Responsive Cyclometalated Iridium(III) Complexes with Boronic Acid Moieties Displaying a Wide Range of Phosphorescence Colors.

Single compounds displaying a wide range of luminescent colors are attractive optical materials for sensor applications. In this study, we present the beneficial combination of a cyclometalated iridium(III) complex scaffold and boronic acid units for designing stimulus-responsive luminescent materials with various emission colors. Five iridium(III) complexes bearing a diboronic acid ligand (bpyB2) were synthesized: Ir(C^N)bpyB2 (C^N=2-phenylpyridine (1), 2-(2,4-difluorophenyl)pyridine (2), 2-(4-methoxyphenyl)pyridine (3), benzo[h]quinoline (4), 1-phenylisoquinoline (5)). The luminescence color of Complexes 1-4 changed in response to the solution pH or saccharide concentration. Complex 1 exhibited a color change from orange to green-blue due to structural alteration of the boronic acid moiety from trigonal to tetrahedral. Furthermore, the luminescence color of Complex 1 changed reversibly due to repetitive changes in the solution pH between 5 and 10, enabling tuning of the luminescence color and pH tracking. Furthermore, the color range was tuned by selecting an appropriate C^N ligand. Time-dependent density functional theory investigations revealed that the dramatic and reversible color changes could be ascribed to a switch in the electronic distribution in the lowest excited state from bpyB2 to C^N. The stimulus-responsive iridium(III) complexes provide a prospective scaffold for future applications in color-tunable optical devices and chemosensing systems.

Bioactive Steroids with Structural Diversity from the South China Sea Soft Coral Lobophytum sp. and Sponge Xestospongia sp.

A chemical investigation of the soft coral Lobophytum sp. and the sponge Xestospongia sp. from the South China Sea led to the isolation of five steroids, including two new compounds (1 and 4) and one known natural product (3). Compounds 1–3 were derived from the soft coral Lobophytum sp., while 4 and 5 were obtained from the sponge Xestospongia sp. The structures of these compounds were determined by extensive spectroscopic analysis, the time-dependent density functional theory–electronic circular dichroism (TDDFT-ECD) calculation method, and comparison with the spectral data previously reported in the literature. The antibacterial and anti-inflammatory activities of isolated compounds were evaluated in vitro. Compounds 1–3, 4, and 5 exhibited weak antibacterial activity against vancomycin-resistant Enterococcus faecium G1, Streptococcus parauberis KSP28, Photobacterium damselae FP2244, Lactococcus garvieae FP5245, and Pseudomonas aeruginosa ZJ028. Moreover, compound 3 showed significant anti-inflammatory activity by inhibiting lipopolysaccharide (LPS)-induced NO production in RAW 264.7 cells, with an IC50 value of 13.48 μM.

Functionalization of Polymer Surfaces for Organic Photoresist Materials.

Photoresists are thin film materials designed to transform an optimal image into a mechanical mask. Diverse exposure techniques such as photolithography induce modifications in the exposed areas that result in solubility changes that can then be selectively removed with appropriate agents (developers). Photoresist materials need to keep pace with the increasingly demand for feature size reduction. Typically, photoresist materials are organic polymers that can present small cross sections to the incoming photons, resulting in poor trade-off between resolution, sensitivity, or line-edge roughness. Photoresists also require a high etch-resistance relative to the substrate material, in order to preserve patterned features after the mechanical mask has been created. The main strategy to improve polymer performance during such processes is functionalization with different elements that can deliver higher efficiencies while keeping the chemical reactivity of the original polymer design. Here we consider a photoresist polymer structure model with general characteristics and investigate the functionalization of the polymer surface using density-functional theory (DFT), with a focus on reactive halogen adsorption. Physical and chemical surface reactions and the corresponding byproducts are identified, obtaining self-limitation thresholds for each specific functionalizing agent. Moreover, spectral signals of the modified polymer surfaces are analyzed in detail, to allow experimental validation of the proposed surface modifications. Finally, using ab initio molecular dynamics (AIMD) and real time time-dependent DFT (rt-TDDFT), we study the interaction of energetic ions and electrons with the modified polymer surfaces, to validate the obtained functionalizations as effectively enhanced etch-resistance strategies. The computational results provide valuable insights on the complex physical, chemical, and dynamic ion and electron interactions with functionalized polymer photoresists, with the immediate consequence of allowing the extraction of definite strategies for improving photoresist polymer performance.

Selective fluoride ion sensing using novel quinoline chemosensor insights into kinetics and molecular logic gate functions

CQHC, a novel colorimetric fluorescent sensor, developed for the selective sensing of ions and well characterised, including SC-XRD. It demonstrated selective sensing for Co2+, Zn2+, Hg2+ and F– using absorbance titration at 420 nm, 446 nm and the binding constants estimated follows the order F– > Co2+ > Hg2+ > Zn2+. On light of this, molecular logic gate was built for CQHC’s selective multi-ion detection. However, fluorescence titration analysis revealed that CQHC is solely selective for F– ions. This conclusion was validated by 1H–NMR titration, clearly showed deprotonation occurs from N3–H. Fluorescent decay titration, kinetic investigations and computational studies all contributed to the selective sensing of F–. According to TD–DFT calculations, added fluoride ion interacts with N3–H proton and deprotonates to generate F–H in the excited state.

Computational Chemistry Study of pH-Responsive Fluorescent Probes and Development of Supporting Software

This study employs quantum chemical computational methods to predict the spectroscopic properties of fluorescent probes 2,6-bis(2-benzimidazolyl)pyridine (BBP) and (E)-3-(2-(1H-benzo[d]imidazol-2-yl)vinyl)-9-(2-(2-methoxyethoxy)ethyl)-9H-carbazole (BIMC). Using time-dependent density functional theory (TDDFT), we successfully predicted the fluorescence emission wavelengths of BBP under various protonation states, achieving an average deviation of 6.0% from experimental excitation energies. Molecular dynamics simulations elucidated the microscopic mechanism underlying BBP’s fluorescence quenching under acidic conditions. The spectroscopic predictions for BIMC were performed using the STEOM-DLPNO-CCSD method, yielding an average deviation of merely 0.57% from experimental values. Based on Einstein’s spontaneous emission formula and empirical internal conversion rate formulas, we calculated fluorescence quantum yields for spectral intensity calibration, enabling the accurate prediction of experimental spectra. To streamline the computational workflow, we developed and open-sourced the EasySpecCalc software v0.0.1 on GitHub, aiming to facilitate the design and development of fluorescent probes.

Plasmon-Enhanced Luminescence of Gold Nanoclusters by Using Silver and Gold Metal Nanostructures.

Plasmonic materials can be utilized as effective platforms to enhance luminescent signals of luminescent metal nanoclusters (LMNCs). Both surface enhanced fluorescence (SEF) and shell-isolated nanoparticle-enhanced fluorescence (SHINEF) strategies take advantage of the localized and increased external electric field created around the plasmonic metal surface when excited at or near their characteristic plasmonic resonance. In this context,we present an experimental and computational study of different plasmonic composites, (Ag) Ag@SiO2 and (Au) Au@SiO2 nanoparticles, which were used to enhance the luminescent signal of Au nanoclusters coated with glutathione (GSH) molecule (Au25GSH NCs). This specific LMNC has recently attracted particular interest due to its luminescent response and characteristic photostability. Our study presents a wide characterization of the optical and morphologic features of the synthetized particles: plasmonic metal nanostructures and Au25GSH NCs through different experimental techniques including UV-Visible, IR, luminescentspectroscopies, along with TEM and AFM microscopies. Additionally, we have carried out computational simulations based on time-dependent density functional theory (TD-DFT) and classical electrodynamics simulation based on Mie Theory to support our experimental findings. In this study, we report up to 3-fold luminescence enhancement of Au25GSH NCs which is mainly attributed to slow dynamics SEF.

Sub-bandgap charge harvesting and energy up-conversion in metal halide perovskites: ab initio quantum dynamics

Metal halide perovskites (MHPs) exhibit unusual properties and complex dynamics. By combining ab initio time-dependent density functional theory, nonadiabatic molecular dynamics and machine learning, we advance quantum dynamics simulation to nanosecond timescale and demonstrate that large fluctuations of MHP defect energy levels extend light absorption to longer wavelengths and enable trapped charges to escape into bands. This allows low energy photons to contribute to photocurrent through energy up-conversion. Deep defect levels can become shallow transiently and vice versa, altering the traditional defect classification into shallow and deep. While defect levels fluctuate more in MHPs than traditional semiconductors, some levels, e.g., Pb interstitials, remain far from band edges, acting as charge recombination centers. Still, many defects deemed detrimental based on static structures, are in fact benign and can contribute to energy up-conversion. The extended light harvesting and energy up-conversion provide strategies for design of novel solar, optoelectronic, and quantum information devices.

Ligand-Induced Intramolecular Cuprophilic and Argentophilic Interactions in Bimetallic Cu(I) and Ag(I) Phosphine Complexes and the Assessment of Their Antityrosinase and Antibacterial Effects.

Binuclear silver(I) and copper(I) complexes, 1 and 5, with bridging diphenylphosphine ligands were prepared. In 1, the silver(I) center is located inside a trigonal plane composed of three phosphorus donors from three separate and bridging dppm ligands. The fourth coordination site is filled with neighboring silver(I) ions. The short Ag···Ag distance, as a result of small bite angles from bridging dppm ligands, was determined to be 2.9463(4) Å. In 5, the Cu···Cu distance is 2.915(6) Å, significantly shorter than that observed in comparable structures. Intramolecular hydrogen bonding interactions in these complexes, such as C-H···F, C-H···O, and O-H···F interactions and π···π interactions, played a significant role in the crystal packing and stability of these molecules in the solid state. Derivatization of 1 and 5 using selected sulfur donor dialkyldithiophosphates gave six novel heteroleptic binuclear complexes. Single crystal X-ray diffraction studies of five of these complexes revealed interesting structural features, including strong metallophilic interactions in 1 and 5 and multiple intramolecular and intermolecular hydrogen bonding interactions. The antibacterial activities of complexes 1, 2, 3, 7, and 8 were also screened against gram-positive (Staphylococcus aureus PTCC 1112) and gram-negative (Escherichia coli PTCC 1330) bacteria. Antityrosinase and hemolytic effects of the selected compounds were also determined. Time-dependent density functional theory (TD-DFT), interaction region indicator (IRI), and fuzzy atom bond order (FBO) analyses of the selected complexes provided insights into the electronic and structural characteristics of the metal complexes.

Theoretical Study on the Internal Conversion Decay Pathways of Bithiophene-Fused Isoquinolines.

In this study, the radiative and nonradiative decay pathways from the first singlet excited states (denoted as S1) of three bithiophene-fused isoquinolines were investigated by using the mixed-reference spin-flip time-dependent density functional theory approach. These isoquinolines, which are prepared via [2 + 2 + 2] cycloaddition reactions between three types of bithiophene-linked diynes and nitriles, exhibit different fluorescence quantum yields in response to the positions of their sulfur atoms. The decay processes, including the fluorescence emission and internal conversion, were considered. In the internal conversion pathway, the minimum energy conical intersection structures between the ground and first singlet excited states (denoted as S0/S1 MECI) of the ring strain for the isoquinoline skeleton and the ring opening of the thiophene skeleton were systematically explored. Dewar-type ring strain resulted in the smallest energy barrier from the equilibrium geometries of the ground state (denoted as S0) to the MECI structures between the S0 and S1 states. The energy difference between the three types of bithiophene-fused isoquinolines at the transition state geometries of the S1 state varies owing to the steric effects between the methyl groups and the hydrogen atom of the thiophene ring, and the excitation energy increases owing to a decrease in aromaticity. In addition, the oscillator strengths of the S0 and S1 states were evaluated at the equilibrium geometries of the S1 state to determine the contribution of the fluorescence process. The obtained theoretical results are consistent with the experimental results.