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In this study, we introduce a theoretical model designed to explore both the photochemical and photothermal behavior of arc plasma radiation-induced ablation in gassing materials. We employ time-dependent density functional theory to analyze the photochemical behavior, while reactive force field molecular dynamics are used to explore the photothermal behavior. The phenomena, behavior and consequences of valence shell electronic excitation are analyzed in terms of ultraviolet (UV) absorption, electron-hole distribution, and Mayer bond order. Based on the photochemical findings, we apply a periodic electric field that corresponds to the vibration frequency of the permanent dipole moment to simulate infrared radiation, and convert UV photon energy into atomic kinetic energy to analyze UV radiation. This atomic-scale insight into photothermal behavior enables us to identify the final composition of ablation gases, including H2, CO, H2O, NH3, as well as specific cyanides, amines, and hydrocarbons. The results of the theoretical model and physical properties indicate that the concentration of hydrogen-containing gases in the ablation gas significantly affects the arc extinguishing capabilities of different polymers. Finally, we propose modification schemes suitable for polymers in power circuit breakers, considering UV absorption and smoke black production. Additionally, we present the potential application of theoretical models for calculating the ablation rate, necessitating further in-depth re-search. [ABSTRACT FROM AUTHOR]

The influence of the composition of the functional used for density functional theory computations on one structural parameter (a dihedral angle) and a spectroscopic parameter (absorption wavelength) is assessed in this study on the basis of two molecules (flavonols). In this kind of molecules, these two parameters should be correlated according to the nature of the electronic transition involved. However, it is shown herein that by varying the proportion of true exchange and correlation while building a functional, it is possible to obtain independently a large range of values for these parameters without any relation with the underlying real values. Therefore, it is concluded that the choice of a functional after a benchmark, especially using user‐defined functionals, should be carried out with great care to avoid such effects. [ABSTRACT FROM AUTHOR]

The outcomes of DFT‐based calculations are here reported to assess the applicability of two synthesized polypyridyl Ru(II) complexes, bearing ethynyl nile red (NR) on a bpy ligand, and two analogues, bearing modified‐NR, in photodynamic therapy. The absorption spectra, together with the non‐radiative rate constants for the S1 – Tn intersystem crossing transitions, have been computed for this purpose. Calculations evidence that the structural modification on the chromophore destabilizes the HOMO of the complexes thus reducing the H‐L gap and, consequently, red shifting the maximum absorption wavelength within the therapeutic window, up to 620 nm. Moreover, the favored ISC process from the bright state involves the triplet state closest in energy, which is also characterized by the highest SOC value and by the involvement of the whole bpy ligand bearing the chromophore in delocalising the unpaired electrons. These outcomes show that the photophysical behavior of the complexes is dominated by the chromophore. [ABSTRACT FROM AUTHOR]

Fungal azaphilones are a broad class of naturally‐occurring pigments with diverse applications. Among the azaphilone pigments, mitorubrins are well recognized for their antiviral, antibacterial, antifungal, antiprotozoal, antidiabetic, and antiaging activities in addition to their well‐known yellow‐orange color. This makes these pigments interesting candidates for use in foods, as cosmetics, and as medicines. In particular, if it is desired to modify the properties of mitorubrin‐based pigments, for example by derivatization, it is essential to have an understanding of the electronic spectra of the parent molecules. We have therefore undertaken a computational study of a series of mitorubrins, comparing our computed results with experimental UV/visible spectra. Both density‐functional theory (DFT) and coupled‐cluster (CC2) methods have been used, and in general, the results are in very good agreement with observation. In order to provide a simple and useful picture of the spectra we analyze the stronger transitions in terms of natural transition orbitals (NTOs). [ABSTRACT FROM AUTHOR]

This work investigated the substitution of the aldehyde with a pyran functional group in D-π-aldehyde dye to improve cell performance. This strategy was suggested by recent work that synthesized D-π-aldehyde dye, which achieved a maximum absorption wavelength that was only slightly off the threshold for an ideal sensitizer. Therefore, DFT and TD-DFT were used to investigate the effect of different pyran substituents to replace the aldehyde group. The pyran groups reduced the dye energy gap better than other known anchoring groups. The proposed dyes showed facile intermolecular charge transfer through the localization of HOMO and LUMO orbitals on the donor and acceptor parts, which promoted orbital overlap with the TiO2 surface. The studied dyes have HOMO and LOMO energy levels that could regenerate electrons from redox potential electrodes and inject electrons into the TiO2 conduction band. The lone pairs of oxygen atoms in pyran components act as nucleophile centers, facilitating adsorption on the TiO2 surface through their electrophile atoms. Pyrans increased the efficacy of dye sensitizers by extending their absorbance range and causing the maximum peak to redshift deeper into the visible region. The effects of the pyran groups on photovoltaic properties such as light harvesting efficiency (LHE), free energy change of electron injection, and dye regeneration were investigated and discussed. The adsorption behaviors of the proposed dyes on the TiO2 (1 1 0) surface were investigated by means of Monte Carlo simulations. The calculated adsorption energies indicates that pyran fragments, compared to the aldehyde in the main dye, had a greater ability to induce the adsorption onto the TiO2 substrate. [ABSTRACT FROM AUTHOR]

Context: Although quantum mechanical calculations have proven effective in accurately predicting UV absorption and assessing the antioxidant potential of compounds, the utilization of computer-aided drug design (CADD) to support sustainable synthesis research of new sunscreen active ingredients remains an area with limited exploration. Furthermore, there are ongoing concerns about the safety and effectiveness of existing sunscreens. Therefore, it remains crucial to investigate photoprotection mechanisms and develop enhanced strategies for mitigating the harmful effects of UVR exposure, improving both the safety and efficacy of sunscreen products. A previous study conducted synthesis research on eight novel hybrid compounds (I–VIII) for use in sunscreen products by molecular hybridization of trans-resveratrol (RESV), avobenzone (AVO), and octinoxate (OMC). Herein, time-dependent density functional theory (TD-DFT) calculations performed in the gas phase on the isolated hybrid compounds (I–VIII) proved to reproduce the experimental UV absorption. Resveratrol-avobenzone structure-based hybrids (I–IV) present absorption maxima in the UVB range with slight differences between them, while resveratrol-OMC structure-based hybrids (V–VIII) showed main absorption in the UVA range. Among RESV-OMC hybrids, compounds V and VI exhibited higher UV absorption intensity, and compound VIII stood out for its broad-spectrum coverage in our simulations. Furthermore, both in silico and in vitro analyses revealed that compounds VII and VIII exhibited the highest antioxidant activity, with compound I emerging as the most reactive antioxidant within RESV-AVO hybrids. The study suggests a preference for the hydrogen atom transfer (HAT) mechanism over single-electron transfer followed by proton transfer (SET-PT) in the gas phase. With a strong focus on sustainability, this approach reduces costs and minimizes effluent production in synthesis research, promoting the eco-friendly development of new sunscreen active ingredients. Methods: The SPARTAN'20 program was utilized for the geometry optimization and energy calculations of all compounds. Conformer distribution analysis was performed using the Merck molecular force field 94 (MMFF94), and geometry optimization was carried out using the parametric method 6 (PM6) followed by density functional theory (DFT/B3LYP/6-31G(d)). The antioxidant behavior of the hybrid compounds (I–VIII) was determined using the highest occupied molecular orbital (εHOMO) and the lowest unoccupied molecular orbital (εLUMO) energies, as well as the bond dissociation enthalpy (BDE), ionization potential (IP), and proton dissociation enthalpy (PDE) values, all calculated at the same level of structural optimization. TD-DFT study is carried out to calculate the excitation energy using the B3LYP functional with the 6-31G(d) basis set. The calculated transitions were convoluted with a Gaussian profile using the Gabedit program. [ABSTRACT FROM AUTHOR]

Context: Nonlinear optics (NLO) is an interesting field that discloses the interaction between intense light and matter, leading to a deeper understanding of NLO phenomena. Organic chromophores are considered as promising materials for NLO due to their exceptional structural versatility, ease of processing, and rapid response to NLO effects. Functional materials based on thiophene have been indispensable in advancing organic optoelectronics. Specifically, dithiophene-based compounds display weaker aromaticity, reduced steric hindrance, and additional sulfur–sulfur interactions. Hence, by utilizing dithieno[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene (DTBDT) as the core structure, designing of a set of organic compounds with D1–π–D2–π–A-type framework, namely ZR1D1–ZR1D8, was carried out in this study. The analysis of frontier molecular orbitals (FMOs) revealed that compound ZR1D2 has the lowest band gap of 1.922 eV among all the investigated chromophores. The correlation of global reactivity parameters (GRPs) with the band gap values indicates that ZR1D2 displays a hardness of 0.961 eV and a softness of 0.520 eV−1. Among the studied compounds, ZR1D2 demonstrated a broad absorption spectrum that extended across the visible region. The maximum absorption wavelengths were observed at 766.470 nm for ZR1D2 and 749.783 nm for ZR1D5. These DTBDT-based dyes exhibit a remarkable NLO response with exceptionally high first hyperpolarizability (βtot) values. Among them, compound ZR1D2 stands out with the highest average linear polarizability (⟨α⟩ = 3.0 × 10−22 esu), first hyperpolarizability (βtot = 4.1 × 10−27 esu), and second hyperpolarizability (γtot = 7.5 × 10−32 esu) values. In summary, this investigation offers valuable insights into the potential use of DTBDT-based organic chromophores, particularly ZR1D2, for advanced applications in NLO. These findings suggest promising opportunities for researchers to synthesize these molecules and utilize these compounds in hi-tech NLO-based applications. Methodology: The density functional theory computations were performed at the M06/6-311G(d,p) functional to explore their structural effects on electronic and NLO findings. Various analyses like highest occupied molecular orbital–lowest unoccupied molecular orbital energy gaps, absorption maxima, density of states, open circuit voltage, binding energies of electrons and holes, and transition density matrix are employed to investigate photovoltaic efficiencies of the derivatives. Different software packages like Avogadro, Multiwfn, Origin, GaussSum, PyMOlyze, and Chemcraft were used to deduce conclusions from the output files. [ABSTRACT FROM AUTHOR]

This study focuses on six D‐π‐A systems, utilizing diverse π‐spacers as bridges. Comprehensive analysis through Density Functional Theory (DFT) and Time‐dependent Functional Theory (TD‐DFT) methods at B3LYP using 6‐31G (d.p) basis set explores geometrical, electrical, optical, photovoltaic, and absorption properties. EHOMO, ELUMO, and energy gap (Egap), for all of these dyes have been determined and discussed using ground state optimization. TD‐DFT calculates optical properties, unveiling enhanced excitation energies and HOMO‐LUMO energy levels, indicative of improved electron injection and dye regeneration processes. Examination of energy gap, open‐circuit voltage (VOC), free energy change (ΔGinject), light harvesting efficiency (LHE), and absorption spectra reveals D4 dye′s lower Egap and robust absorption in the visible spectrum. Molecular tailoring emerges as a promising technique for optimizing D‐π‐A sensitizer design, offering potential advancements in DSSCs applications. [ABSTRACT FROM AUTHOR]

Betanin (Bn), a natural dye in the Betalains family, predominantly takes on a cationic form known as Bn+. However, it exists in a neutral state as Bn_C2, Bn_C15, and Bn_C17 by losing an H+ from one of its carboxylic acids. Density functional theory (DFT) and Time‐dependent density functional theory (TD‐DFT) studies evaluate the efficiency of each betanin form and pinpoint the most probable anchoring point to TiO2. The Bn_C17 variant stands out as a highly promising candidate for DSSC cells, demonstrating a distinctive combination of electron injection efficiency, electrochemical performance, hole transport capabilities, and photovoltaic behavior. Considering factors like adsorption energy, binding mode, structural compatibility, electronic properties, and absorption characteristics, Bn_C17@TiO2 emerges as the most favorable dye@TiO2 complex among the studied betanin forms for DSSC applications. Contrastingly, the C2‐COOH anchoring point presents challenges with monodentate binding, a different orientation, and potential load distribution issues. This behavior, resembling that of a p‐type dye, differs from the n‐type behavior exhibited by the C15‐COOH and C17‐COOH forms, making the latter two more suitable as sensitizers. Consequently, C2‐COOH may not be the optimal anchoring point for TiO2 in the investigated betanin forms, especially when compared to the more favorable C17‐COOH anchoring point. [ABSTRACT FROM AUTHOR]

Betanin (Bn), a natural dye in the Betalains family, predominantly takes on a cationic form known as Bn+. However, it exists in a neutral state as Bn_C2, Bn_C15, and Bn_C17 by losing an H+ from one of its carboxylic acids. Density functional theory (DFT) and Time‐dependent density functional theory (TD‐DFT) studies evaluate the efficiency of each betanin form and pinpoint the most probable anchoring point to TiO2. The Bn_C17 variant stands out as a highly promising candidate for DSSC cells, demonstrating a distinctive combination of electron injection efficiency, electrochemical performance, hole transport capabilities, and photovoltaic behavior. Considering factors like adsorption energy, binding mode, structural compatibility, electronic properties, and absorption characteristics, Bn_C17@TiO2 emerges as the most favorable dye@TiO2 complex among the studied betanin forms for DSSC applications. Contrastingly, the C2‐COOH anchoring point presents challenges with monodentate binding, a different orientation, and potential load distribution issues. This behavior, resembling that of a p‐type dye, differs from the n‐type behavior exhibited by the C15‐COOH and C17‐COOH forms, making the latter two more suitable as sensitizers. Consequently, C2‐COOH may not be the optimal anchoring point for TiO2 in the investigated betanin forms, especially when compared to the more favorable C17‐COOH anchoring point. [ABSTRACT FROM AUTHOR]

Through molecular recognition, drugs can interact and complex with macromolecules circulating in the body. The serum albumin transport protein, found in several mammals, has several interaction sites where these molecules can be located. The drug sulfasalazine (SSZ) is known in the literature to complex at drug site 1 (DS1) in human serum (HSA) and bovine serum (BSA) proteins. This complexation can be studied using various spectroscopic techniques. With the techniques used in this work, absorption in the ultraviolet and visible regions (UV–Vis) and electronic circular dichroism (ECD), a significant difference was observed in the results involving HSA and BSA. The application of theoretical methodologies, such as TD‐DFT and molecular docking, suggests that the conformation that SSZ assumes in DS1 of the two proteins is different, which exposes it to different amino acid residues and different hydrophobicities. This difference in conformation may be related to the location of DS1 where the drug interacts or to the possibility of SSZ moving in the BSA site, due to its larger size, and moving less freely in HSA. [ABSTRACT FROM AUTHOR]

In this study, it is considered three anthracene derivatives, characterized meticulously in terms of their chemical structure and product purity. Extensive quantum chemical calculations are conducted to elucidate their optical and nonlinear optical properties, shedding light on the mechanism of photoinduced conformational transformation, a pivotal discovery in this research. Experimental analyses encompassed fundamental optical properties and advanced nonlinear optical phenomena, including z‐scan experiments, second harmonic generation (SHG), and third harmonic generation (THG). Remarkably, a groundbreaking all‐optical switching phenomenon in these materials is experimentally validated, marking a significant advancement and contributing to their potential applications. [ABSTRACT FROM AUTHOR]

Using the Polarizable Continuum Model (PCM), we investigated the solvent effect on the spectroscopic properties of three different groups of molecules with potential antitumor: three endocannabinoids—Anandamide, Met‐Anandamide, and Chloroethylamide; three phytocannabinoid—Cannabichromene, Cannabidiol and Cannabigerol—and two flavonoids—Morin and Quercetin. Our findings indicate increases in the dipole moment whereas the optical absorption spectrum shows a small effect of water on absorption peaks for all molecules, but with an impact on absorption intensity for some compounds. Our calculations indicated NMR shifts up to 7 ppm for carbon atoms and between 11 and 63 ppm for the oxygen ones. [ABSTRACT FROM AUTHOR]

Strongly polarized donor‐acceptor‐donor′ diketopyrrolopyrroles, differing in the type of key donor moiety, were designed and synthesized to examine how this affects the non‐radiative decay. Dyes possessing less electron‐rich N‐carbazolyl substituents are characterized by strong yellow emission from a locally excited (LE) state, whereas replacing this donor with more electron‐rich N‐phenothiazinyl substituent changes the relative position of charge‐transfer (CT) and LE states, leading to weaker, reddish‐orange fluorescence. As a result, there is solvent‐dependent charge‐transfer emission shifted to as far as 700 nm. The opening of the intersystem crossing channel to the triplet state possessing CT character is the most likely cause of the fluorescence quantum yield variation in some cases. These results reveal that the fate of molecules in their excited state can be fine‐tuned by very small structural changes. [ABSTRACT FROM AUTHOR]

One useful technique for increasing the efficiency of organic dye-sensitized solar cells (DSSCs) is to extend the π-conjugated bridges between the donor (D) and the acceptor (A) units. The present study used the DFT and TD–DFT techniques to investigate the effect of lengthening the polyene bridge between the donor N, N-dimethyl-anilino and the acceptor dicyanovinyl. The results of the calculated key properties were not all in line with expectations. Planar structure was associated with increasing the π-conjugation linker, implying efficient electron transfer from the donor to the acceptor. A smaller energy gap, greater oscillator strength values, and red-shifted electronic absorption were also observed when the number of polyene units was increased. However, some results indicated that the potential of the stated dyes to operate as effective dye-sensitized solar cells is limited when the polyene bridge is extended. Increasing the polyene units causes the HOMO level to rise until it exceeds the redox potential of the electrolyte, which delays regeneration and impedes the electron transport cycle from being completed. As the number of conjugated units increases, the terminal lobes of HOMO and LUMO continue to shrink, which affects the ease of intramolecular charge transfer within the dyes. Smaller polyene chain lengths yielded the most favorable results when evaluating the efficiency of electron injection and regeneration. This means that the charge transfer mechanism between the conduction band of the semiconductor and the electrolyte is not improved by extending the polyene bridge. The open circuit voltage (VOC) was reduced from 1.23 to 0.70 V. Similarly, the excited-state duration (τ) decreased from 1.71 to 1.23 ns as the number of polyene units increased from n = 1 to n = 10. These findings are incompatible with the power conversion efficiency requirements of DSSCs. Therefore, the elongation of the polyene bridge in such D-π-A configurations rules out its application in solar cell devices. [ABSTRACT FROM AUTHOR]

In organisms, amino acids usually use water as a solvent which is an important component for cell formation. In this environment, the formation of intermolecular hydrogen bonds will affect the structure and properties of amino acids and water molecules. In order to study its properties in the ground state and excited state, in this paper, we use density functional theory（DFT) and time-dependent density functional theory（TD-DFT) to analyze the electrostatic potential, bond length, natural bond orbital（NBO) charge, Atoms In Molecules（AIM), Wiberg bond order b, infrared（IR) spectroscopy, hole-electron orbits of intermolecular hydrogen bonds between glycine and H2O in the ground and excited states, the hole electron orbit and the electron transfer between ground state and excited state are studied theoretically. The results show that the intermolecular hydrogen bond formation will lead to the change of molecular structure and the shift of infrared spectral vibration frequency. In the excited states, the intermolecular hydrogen bond is strengthened or weakened to different degrees. The results provide a theoretical basis for forming hydrogen bonds and the study of intermolecular hydrogen bonds in excited states. [ABSTRACT FROM AUTHOR]

This study employs density functional theory (DFT) calculations at the B3LYP/6-311+g(d,p) level to investigate the interaction of XH3 gases (X = N, P, As) with the Mn-phthalocyanine molecule (MnPc). Grimme's D3 dispersion correction is applied to consider long-range interactions. The adsorption behavior is explored under the influence of an external static electric field (EF) ranging from −0.514 to 0.514 V/Å. Chemical adsorption of XH3 molecules onto the MnPc molecule is confirmed. The adsorption results in a significant decrease in the energy gap (Eg) of MnPc, indicating the potential alteration of its optical properties. Quantum theory of atoms in molecules (QTAIM) analysis reveals partially covalent bonds between XH3 and MnPc, and the charge density differenc (Δρ) calculations suggest a charge donation-back donation mechanism. The UV-vis spectrum of MnPc experiences a blue shift upon XH3 adsorption, highlighting MnPc's potential as a naked-eye sensor for XH3 molecules. Thermodynamic calculations indicate exothermic interactions, with NH3/MnPc being the most stable complex. The stability of NH3/MnPc decreases with increasing temperature. The direction and magnitude of the applied electric field (EF) play a crucial role in determining the adsorption energy (Eads) for XH3/MnPc complexes. The Eg values decrease with an increasing negative EF, which suggests that the electrical conductivity (σ) and the electrical sensitivity (ΔEg) of the XH3/MnPc complexes are influenced by the magnitude and direction of the applied EF. Overall, this study provides valuable insights into the suggested promising prospects for the utilization of MnPc in sensing applications of XH3 gases. [ABSTRACT FROM AUTHOR]

In this work, we investigate the spectroscopic properties of photochromic alexandrite and cordierite by TD‐DFT. The objective is to assess the TD‐DFT for the simulation of pleochroism (change of color depending on the crystallographic direction of the observation) and the change of color as a function of the light source. For these simulations, we compared an embedding where dangling bonds are saturated by hydrogen atoms and an electrostatic embedding. The electrostatic embedding provided numerically more stable results and allowed a good reproduction of the pleochroism of cordierite, based on a Fe2+‐Fe3+ intervalence charge transfer transition. However, the pleochroism of alexandrite is not as well reproduced, suggesting that TD‐DFT has some difficulties to reproduce the anisotropy of the transition dipole moment, an aspect that is not deeply documented in the literature. [ABSTRACT FROM AUTHOR]

The coordination capability of two N,C,N pincer coordinated stibinidenes, i. e. bis(imino)‐ [2,6‐(DippN=CH)2C6H3]Sb (1) or imino‐amino‐ [2‐(DippN=CH)‐6‐(DippNHCH2)C6H3]Sb (2) toward palladium(II) and platinum(II) centers was examined. In the course of this study, seven new square‐planar bis(stibinidene) complexes were synthesized and characterized by NMR, IR, Raman, UV‐vis spectroscopy and single crystal (sc)‐X‐ray diffraction analysis. In all cases, both stibinidene ligands 1 or 2 adopt trans positions, but differ significantly in the torsion angle describing mutual orientation of aromatic rings of the stibinidenes along the Sb−Pd/Pt−Sb axes. Furthermore, majority of complexes form isomers in solution most probably due to a hindered rotation around Sb−Pd/Pt bonds caused by bulkiness of 1 and 2. This phenomenon also seems to be influenced by the absence/presence of a pendant −CH2NH− group in 1/2 that is able to form intramolecular hydrogen bonds with the adjacent chlorine atom(s) attached to the metal centers. The whole problem was subjected to a theoretical study focusing on the role of hydrogen bonds in structure architecture of the complexes. To describe the UV‐vis spectra of these highly coloured complexes, TD‐DFT calculations were employed. These outline differences between the stibinidene ligands, the transition metals as well as between the charge of the complexes (neutral or anionic). [ABSTRACT FROM AUTHOR]

Density functional study (DFT) is performed for understanding the reactivity, aromaticity, and UV-visible absorption spectra of chrysene-based materials. Effect of BN doping on the said parameters are analyzed along with the effect of –Me (methyl), –OH (hydroxyl), –CHO (formyl) –COOH (carboxyl) and –CN (cyano) substituents. Global reactivity parameters viz. energy of HOMO (EHOMO), global hardness (η), chemical potential (μ) and electrophilicity (ω) are computed. Nucleus independent chemical shifts (NICS) values are estimated to study the variation in aromaticity. Time dependent density functional theory (TD-DFT) is used to study the UV–Visible absorption spectra. Effects of BN doping and substituents on corresponding dipole moments and band gaps are also analyzed. Presence of BN unit and/or substituents induced considerable impact on global reactivity, dipole moment, band gap and aromaticity of the chosen systems, especially for BN doped chrysene at the edge. Absorption spectra which are red shifted in presence of BN and substituents are mostly found within the UV-region. [ABSTRACT FROM AUTHOR]

New renewable energy sources, like solar cells, demonstrated to have environmental difficulties, pricing efficiency and other problems. In this study, the hole–electron theory has been applied by DFT and TD-DFT modeling to simulate an organic solar cell (OSC) with the special capabilities. This designed OSC applies a π-donor-π-acceptor system. It was demonstrated that Heme molecule could be chosen as an acceptor agent in this system. The modeled system has been modified by an efficient acceptor with four C60 fullerenes. This modeled system is considerable as an important charge and electron transfer at visible wavelengths of approximately 574 nm. The investigations were conducted in the two ground and excited states. The results have given a comprehensive picture of how the discussed OSC acts. The electron-donating part of this OSC actually consists of two S-donors that are connected by pyrazino[2,1,6-de]quinolizine linker. The energies of the all LUMO orbitals from donor part, Heme molecule, C60 and Heme + C60 (acceptor part) are cascaded from top to bottom. [ABSTRACT FROM AUTHOR]

The molecular geometry, electronic structure, and absorption spectra of some important phenyl derivatives are investigated by using DFT and TD‐DFT with B3LYP and CAM‐B3LYP functional. The highest HOMO–LUMO energy gap, Non‐linear optical properties of dipole moment, polarizability, and hyperpolarizability are calculated. In both methods hyperpolarizability PDP values (16.77 × 10−30 and 16.59 × 10−30 esu) are higher than PDNA, PDN, and MPAN dye. The Molecular electrostatic potential shows that PDNA dye has more electronegative potential. Comparing all the dyes, PDP dye shows a higher light harvesting efficiency in the UV–vis region. The vibrational frequencies are assigned based on the potential energy distribution (PED) using the VEDA‐4 program. [ABSTRACT FROM AUTHOR]

In this study, we present a comprehensive investigation of 2-amino-4,6-diphenylnicotinonitriles (APNs, 1–6), including their synthesis, cytotoxicity against breast cancer cell lines, and photophysical properties. Compound 3 demonstrates exceptional cytotoxicity, surpassing the potency of Doxorubicin. The fluorescence spectra of the synthesized 1–6 in different solvents reveal solvent-dependent shifts in the emission maximum values, highlighting the influence of the solvent environment on their fluorescence properties. A quantum chemical TD-DFT analysis provides insights into the electronic structure and fluorescence behavior of 1–6, elucidating HOMO-LUMO energy gaps, electronegativity values, and dipole moments, contributing to a deeper understanding of their electronic properties and potential reactivity. These findings provide valuable knowledge for the development of APNs (1–6) as fluorescent sensors and potential anticancer agents. [ABSTRACT FROM AUTHOR]

This study conducts a thorough theoretical investigation of Thermally Activated Delayed Fluorescence (TADF) in phenothiazine‐based systems, examining ten molecular configurations recognized experimentally as TADF‐active. Employing Time‐Dependent Density Functional Theory (TD‐DFT), our analysis spans the investigation of singlet‐triplet energy gaps (ΔEST), spin‐orbit coupling, and excitation characteristics using Multiwfn. This approach not only validates the adherence to El Sayed's rule across these systems but also provides a detailed understanding of charge transfer dynamics, as visualized through heat maps. A significant aspect of our study is the exploration of different oxidation states of sulfur and site substitutions on phenothiazine. This systematic variation aims to identify additional TADF‐active compounds, drawing parallels with properties characterizing other known TADF emitters. Our investigation into Reverse Intersystem Crossing (rISC) rates and the analysis of dihedral angles in relation to ΔEST values offer nuanced insights into the TADF behaviours of these molecules. By integrating rigorous computational analysis with practical implications, we provide a foundational understanding that enhances the design and optimization of phenothiazine‐based materials for optoelectronic applications. This work not only advances our theoretical understanding of TADF in phenothiazine derivatives but also serves as a guide for experimentalists and industry professionals in the strategic design of new TADF materials. [ABSTRACT FROM AUTHOR]

Very recently, N-heterocyclic carbenes (NHCs) have found a wide range of applications in the fields of catalysis and nonlinear optics. Herein, we have employed 1,3-bis-(1(S)-benzyl)-4,5-dihydro-imidazol-based carbene as a reference molecule and substituted one H atom from each CH2 of the benzyl groups in both sides by CH3, NH2, and CF3 to study the thermodynamic and opto-electronic properties of NHCs theoretically. It was observed that the enthalpy (H), Gibb's free energy (G), specific heat capacity (Cv), and entropy (S) increase significantly in the presence of the electron-withdrawing groups compared to the electron-donating groups. The IR active in-plane bending vibrations of the CH (NHC) group are shifted to the higher frequency region for the considered substituted molecules compared to the reference carbene. The analysis of the electronic properties shows that the CH3-substituted carbene is more reactive for catalytic activities compared to other NHCs. The calculated nonlinear optical (NLO) properties reveal that the NH2-substituted NHC has the largest hyperpolarizability value whereas the CH3-substituted NHC has the largest dipole moment and polarizability among all, making them potential candidates for the development of NLO materials. [ABSTRACT FROM AUTHOR]

The analysis to plan for high-efficiency with affordable molecules such as coumarin, prop-1-ene with 2-cyano-N-hydroxyacrylamide (A1), 2-cyanoprop-2-enedithioic acid (A2), 1-cyanovinylphosphonic acid (A3) and 1-cyanoethenesulfinic acid (A4) are one of the most important aspects of improving the non-linear optical (NLO) property besides dye-sensitized solar cells (DSSCs) applications. NKX-2311 has been taken as a literature molecule, it contains coumarin as a donor moiety (D), prop-1-ene as a π-spacer (π) and cyanoacrylic acid as an acceptor moiety (A). The three fragments that make up the D-π-A structure. The family of A1-A4 metal-free organic coumarin NKX-2311 dye derivatives have examined for applications involving optoelectronics in this research. Density functional theory (DFT) and time-dependent DFT (TD-DFT) techniques utilizing quantum chemical calculations, the molecular electronic structures, ultra-violet visible (UV–Vis) absorption, transition density matrix (TDM), electron–hole mobilities (reorganization energies) and photovoltaic (PV) characteristics of the A1-A4 sensitizers have been calculated. For optoelectronic devices, the effect of chemical alteration on the UV–Vis spectra about PV parameters of the NKX-2311 were illustrated. The performance of hybrid functionals such as B3LYP, CAM-B3LYP and ωB97XD was assessed to compare with the absorption wavelength of NKX-2311. The B3LYP method and NKX-2311 have had a superior fit based on the selected functionals. Consequently, the B3LYP/6-31G(d) theory has been used to study the excited state computations of A1-A4 dyes at UV–Vis wavelengths. The findings demonstrate that A2 dye has a smaller energy gap and that UV–Vis spectra were constantly redshifted. According to the computational outcomes, the A1-A4 sensitizers can respond positively to the processes of dye regeneration and electron injection based on their lowest unoccupied and highest occupied molecular orbitals (LUMOs and HOMOs), respectively. A2 dye has the greatest hole mobility due to its lowest λ + value of 0.1701 eV, while A1 dye has extreme electron mobility due to its lowest λ - value of 0.2273 eV. The NLO property of molecules A1-A4 has been calculated by two ways such as polarizability and first-order hyperpolarizability. The most promising candidate for NLO performance has been identified as the dye with computed values of A2. The results would serve as a useful resource for any upcoming demands and also more advantageous for obtaining optoelectronic applications. [ABSTRACT FROM AUTHOR]

In this work, the geometrical, optical, and phosphorescence properties of four complexes with general formula [dRpypy—C(OCH3)R′—dRpypy]Pt, with Pt-1 (R = F, R′ = methyl), Pt-2 (R = F, R′ = hexyl), Pt-3 (R = methoxy, R′ = methyl) and Pt-4 (R = methoxy, R′ = hexyl), were studied using the B3PW91 and TD-B3PW91 methods. The effect of the double substitution R and R′ on the electronic properties of the four complexes has been investigated. Replacing the two fluorine atoms with the two methoxy groups modifies the shape of the UV–vis spectra and red shift the phosphorescence spectra, while the substituents on the linker R′ do not induce changes in both absorption and phosphorescence spectra. Normal modes involved in the vibronic structure were identified and analyzed using adiabatic Hessian approaches according to the Franck–Condon approximation. The computed phosphorescence wavelengths agree with the observed ones and indicate that the fluorinated complexes exhibit a bright light blue color, while the methoxy complexes display a light spring green color. Further, temperature effects on simulated phosphorescence spectra were studied. [ABSTRACT FROM AUTHOR]

Abstract This study focuses on six D‐π‐A systems, utilizing diverse π‐spacers as bridges. Comprehensive analysis through Density Functional Theory (DFT) and Time‐dependent Functional Theory (TD‐DFT) methods at B3LYP using 6‐31G (d.p) basis set explores geometrical, electrical, optical, photovoltaic, and absorption properties. EHOMO, ELUMO, and energy gap (Egap), for all of these dyes have been determined and discussed using ground state optimization. TD‐DFT calculates optical properties, unveiling enhanced excitation energies and HOMO‐LUMO energy levels, indicative of improved electron injection and dye regeneration processes. Examination of energy gap, open‐circuit voltage (VOC), free energy change (ΔGinject), light harvesting efficiency (LHE), and absorption spectra reveals D4 dye′s lower Egap and robust absorption in the visible spectrum. Molecular tailoring emerges as a promising technique for optimizing D‐π‐A sensitizer design, offering potential advancements in DSSCs applications.

Silicon, traditionally known as an indirect band gap semiconductor, unveils intriguing properties at the nanoscale, stemming from deviations from k-conservation rules within nanostructures. In our study, we scrutinized four hydrogenated Si 0D-nanostructures—Si10H16, Si14H20, Si18H24, and Si22H28—to unravel their dynamic stability under thermal fluctuations and optical characteristics. We initiated our exploration by employing the TD-DFT framework to generate and analyze the optical properties of these geometrically optimized nanostructures. Simultaneously, we conducted ab initio molecular dynamics simulations to examine the structural robustness and thermal stability of the four structures. Leveraging the Car-Parrinello molecular dynamics approach within the Quantum ESPRESSO open software suite, we observed temperature evolution and stability differences among the nanostructures at targeted temperatures 40 and 300 K. Our subsequent investigation delved into the Turbo-Lanczos time-dependent DFT method, unraveling the optical properties and excited-state dynamics of hydrogenated Si nanostructures. The results unveiled shifts towards higher energy absorption edges E0, accompanied by alterations in the permittivity tensor, complex refractive index, oscillator strength, and reflectivity. Notably, the analysis revealed an enlarged HOMO-LUMO gap, distinctive from bulk Si. Furthermore, our models predicted the elimination of phase-dependent E1/E2 optical transition peaks in the imaginary part of the dielectric function, and a gradual decrease in the low-frequency dielectric response with increased hydrogenation of the amorphous structures. These findings underscore the promising applications of hydrogenating Si nanostructures in diverse technological domains such as optoelectronics, memristors, sensors, and quantum computing. Their tunable optical properties, size-dependent behaviors, and compatibility with existing silicon-based devices make them particularly appealing for next-generation technologies.

The tautomerism in the title compound as a potential long-range proton transfer (PT) switch has been studied by using the DFT and TD-DFT approaches. The data show that in aprotic solvents, the enol tautomer dominates, while the increase in the content of the keto tautomer (short-range PT) rises as a function of polarity of the solvent. In ethanol, due to specific solute–solvent stabilization through intermolecular hydrogen bonding, a substantial amount of the keto forms exists in solution. The irradiation leads to two competitive processes in the excited state, namely ESIPT and trans/cis isomerization around the azomethine bond as in other structurally similar Schiff bases. The studied compound is not suitable for bistable tautomeric switching, where long-range PT occurs, due to the difficult enolization of the coumarin carbonyl group.

Abstract This study investigates the structural intricacies and properties of single-walled nanotubes (SWNT) and double-walled nanotubes (DWNT) composed of hexagonal boron nitride (BN) and carbon (C). Doping with various atoms including light elements (B, N, O) and heavy metals (Fe, Co, Cu) is taken into account. The optimized configurations of SWNT and DWNT, along with dopant positions, are explored, with a focus on DWNT-BN-C. The stability analysis, employing binding energies, affirms the favorable formation of nanotube structures, with DWNT-C emerging as the most stable compound. Quantum stability assessments reveal significant intramolecular charge transfer in specific configurations. Electronic properties, including charge distribution, electronegativity, and electrical conductivity, are examined, showcasing the impact of doping. Energy gap values highlight the diverse electronic characteristics of the nanotubes. PDOS analysis provides insights into the contribution of atoms to molecular orbitals. UV–Vis absorption spectra unravel the optical transitions, showcasing the influence of nanotube size, dopant type, and location. Hydrogen storage capabilities are explored, with suitable adsorption energies indicating favorable hydrogen adsorption. The desorption temperatures for hydrogen release vary across configurations, with notable enhancements in specific doped DWNT-C variants, suggesting potential applications in high-temperature hydrogen release. Overall, this comprehensive investigation provides valuable insights into the structural, electronic, optical, and hydrogen storage properties of BN and C nanotubes, laying the foundation for tailored applications in electronics and energy storage.

A series of sulfonamide azobenzenes bearing alkyl substituents of increasing steric bulk at the position ortho to the N=N bond and their corresponding chloro(hexamethylbenzene)ruthenium(II) complexes were synthesized. The latter bearing mono‐substituted ligands exhibited an exocyclic azo bond under the E configuration, and underwent reversible E→Z photoisomerization upon irradiation with visible light, followed by thermal Z→E back isomerization upon resting in the dark at 20 °C. In contrast, the corresponding 2,6‐dimethyl substituted azobenzene complex, while also exhibiting an exocyclic azo bond, was isolated as the Z‐isomer and underwent uncommon solvent dependent irreversible photodissociation of azobenzene ligand upon visible light irradiation. Valuable insights into the photophysical and structural properties of these complexes were gained by combination of computational and X‐ray diffraction studies. [ABSTRACT FROM AUTHOR]

We here study the effect that a lowering of the pH has on the excited state processes of cytidine and a cytidine/cytidine pair in solution, by integrating time‐dependent density functional theory and CASSCF/CASPT2 calculations, and including solvent by a mixed discrete/continuum model. Our calculations reproduce the effect of protonation at N3 on the steady‐state infrared and absorption spectra of a protonated cytidine (CH+), and predict that an easily accessible non‐radiative deactivation route exists for the spectroscopic state, explaining its sub‐ps lifetime. Indeed, an extremely small energy barrier separates the minimum of the lowest energy bright state from a crossing region with the ground electronic state, reached by out‐of‐plane motion of the hydrogen substituents of the CC double bond, the so‐called ethylenic conical intersection typical of cytidine and other pyrimidine bases. This deactivation route is operative for the two bases forming an hemiprotonated cytidine base pair, [CH·C]+, the building blocks of I‐motif secondary structures, whereas interbase processes play a minor role. N3 protonation disfavors instead the nπ* transitions, associated with the long‐living components of cytidine photoactivated dynamics. [ABSTRACT FROM AUTHOR]

Anthropogenic air and water pollution are two of the world's most serious public health threats, causing around 9 million fatalities each year. Accordingly, CuO, ZnO, and CuO@ZnO core/shell structures were optimized utilizing the time-dependent density functional theory (TD-DFT) method to study the effect of CuO@ZnO core/shell on the sensitivity of carboxymethyl cellulose sodium (CMC). Absorption spectra and optical band gap (Eg) have been investigated utilizing the TD-DFT method. The calculated Eg values for CuO and ZnO equal 1.23 and 3.29 eV, respectively, which agree well with those reported in the literature. The effects of H2S gas and methylene blue dye (MB) adsorption on the electronic characteristics of dimer CMC /CuO@ZnO structures were investigated in terms of TDM, HOMO/LUMO energy, and molecular electrostatic potential (MESP). The TDM in dimer CMC/CuO@ZnO structure was increased to 72.152 and 67.606 Debye, while ΔE was reduced by 6.42% and 82.57% due to the adsorption of H2S and MB dye, respectively. This means that it has a faster response to MB than to H2S. Additionally, MESP confirms the increased reactivity of dimer CMC/CuO@ZnO due to the adsorption process. As a result, dimer CMC/CuO@ZnO structures appear to be attractive candidates for H2S and MB dye sensing applications. [ABSTRACT FROM AUTHOR]

The optical properties of Malachite green (Mg) dye were examined experimentally, including absorption, optical energy gab, refractive index, dielectric constant, optical conductivity and emission spectra in various solvents. Additionally, several significant photophysical parameters were evaluated, including the extinction coefficient (ε), the energy yield of fluorescence (Ef), the length of attenuation Λ (λ), oscillator strength (f), quantum yield (Øf), fluorescence lifetime ( τ f ), decay rate radiative constant (kr), and the dipole moment (μ) in addition to absorption and emission cross-sections (σa) and (σe) respectively. Time Dependent Density function theory (TD-DFT) computations were used to generate the theoretical absorption spectra of the (Mg) compound. The energy gap (Eg), electron density, and electrostatic potential were also simulated. [ABSTRACT FROM AUTHOR]

Donor–acceptor dyads based on BODIPYs have been recently employed to enhance the formation of triplet excited states with the process of spin–orbit charge transfer intersystem crossing (SOCT-ISC) which does not require introduction of transition metals or other heavy atoms into the molecule. In this work we compare two donor–acceptor dyads based on meso-naphthalenyl BODIPY by combining experimental and computational investigations. The photophysical and electrochemical characterization reveals a significant effect of alkylation of the BODIPY core, disfavoring the SOCT-ISC mechanism for the ethylated BODIPY dyad. This is complemented with a computational investigation carried out to rationalize the influence of ethyl substituents and solvent effects on the electronic structure and efficiency of triplet state population via charge recombination (CR) from the photoinduced electron transfer (PeT) generated charge-transfer (CT) state. Time dependent-density functional theory (TD-DFT) calculations including solvent effects and spin–orbit coupling (SOC) calculations uncover the combined role played by solvent and alkyl substitution on the lateral positions of BODIPY. [ABSTRACT FROM AUTHOR]

The tautomerism in the title compound as a potential long-range proton transfer (PT) switch has been studied by using the DFT and TD-DFT approaches. The data show that in aprotic solvents, the enol tautomer dominates, while the increase in the content of the keto tautomer (short-range PT) rises as a function of polarity of the solvent. In ethanol, due to specific solute–solvent stabilization through intermolecular hydrogen bonding, a substantial amount of the keto forms exists in solution. The irradiation leads to two competitive processes in the excited state, namely ESIPT and trans/cis isomerization around the azomethine bond as in other structurally similar Schiff bases. The studied compound is not suitable for bistable tautomeric switching, where long-range PT occurs, due to the difficult enolization of the coumarin carbonyl group. [ABSTRACT FROM AUTHOR]

Triarylhydrazones represent an attractive class of photochromic compounds offering many interesting features including high molar absorptivity, good addressability, and extraordinary thermal stability. In addition, unlike most other hydrazone‐based photoswitches, they effectively absorb light above 365 nm. However, previously prepared triaryhydrazones suffer from low quantum yields of the Z→E photoisomerization. Here, we have designed a new subclass of naphthoyl‐benzothiazole hydrazones that balance the most beneficial features of previously reported naphthoyl‐quinoline and benzoyl‐pyridine triarylhydrazones. These preserve the attractive absorption characteristics, exhibit higher thermal stability of the metastable form than the former and enhance the rate of the Z→E photoisomerization compared to the later, as a result of the weakening of the intramolecular hydrogen bonding between the hydrazone hydrogen and the benzothiazole moiety. Introducing the benzothiazole motif extends the tunability of the photochromic behaviour of hydrazone‐based switches. [ABSTRACT FROM AUTHOR]

This work is a development and extension of the previous one (DOI: 10.1039/d3cp00882g). Here, H‐dimers of acridine (acridine orange—AO and proflavine—PF), thiazine (methylene blue—MB and thionine—TH), and oxazine (brilliant cresyl blue—BCB and Nile blue—NB) dyes were modeled using hybrid functionals with a large proportion of exact Hartree–Fock exchange and long‐range correction. It turned out that nine functionals (LC‐ωHPBE, M06HF, M052X, M062X, M08HX, M11, MN15, SOGGA11X, and ωB97XD) reliably stabilize these molecular aggregates in both the ground and excited states. In addition, these functionals ensure that the conditions for transition moments (M(dimer) ≈ 2$$ \sqrt{2} $$M(monomer) from strong coupling theory for H‐aggregates) and absorption maxima (λmax(dimer) < λmax(monomer) from Kasha exciton theory) are met. The S2 excited state stabilizes the H‐dimers more strongly than the ground state, while the S1 state stabilizes even more than S2. This is due to the large overlap between the corresponding molecular orbitals (LUMO > HOMO−1 > HOMO). When calculating the vibronic absorption spectra, the best agreement with the experiment for AO2, PF2, and NB2 showed the M08HX functional, and M11—for MB2 and BCB2. For dye monomers, these functionals gave the worst agreement, and MN15 demonstrated the closest similarity to the experiment. Vibronic absorption spectra for AO2, MB2, BCB2, and NB2 were calculated for the first time. The exciton splitting is calculated, which for MB2 is in good agreement with the experimental value. [ABSTRACT FROM AUTHOR]

Synthesis and characterization of configurationally stable chiral aza[7]helicene‐functionalized trityl radicals are reported. To overcome the problem of incomplete radical formation after coupling the trityl radical to the chiral aza[7]helicenes in a nucleophilic aromatic substitution, this study instead employs Pd‐catalyzed C‐N cross‐coupling. In contrast to the conventional approach, the open‐shell character is retained allowing quantitative yield of the radical. The obtained dinaphthocarbazole and diphenanthrocarbazol‐functionalized tris(trichlorophenyl)methyl (TTM) radicals can be separated into the respective enantiomers. The resulting chiral radicals exhibit photoluminescence quantum yields as high as 43% and circularly polarized luminescence. Time‐dependent density functional theory (TD‐DFT) calculations support the experimental findings. The newly reported aza[7]helicene‐based radicals hold promise for advanced optoelectronic as well as quantum technological applications. [ABSTRACT FROM AUTHOR]

The dinuclear polypyridyl complex [{Ru(bipy)2}2(µ-L)](PF6)4, where bipy = 2,2'-bipyridine and L = 2,6-bis[(1,10-phenantroline-5-amine)methyl]pyridine, was prepared and characterized by UV-Vis and infrared spectroscopy. Geometry optimization revealed the possibility of three conformers, and time-dependent density functional theory calculations provided access to the correct excited state composition and unambiguous assignment of the characteristic metal-ligand charge transfer transitions. [ABSTRACT FROM AUTHOR]

The nonlinear optical (NLO) insights of triarylpyrazoline‐based (Z)‐2‐(2‐((7‐(4‐(5‐[2,4‐dimethylphenyl]‐1‐phenyl‐4,5‐dihydro‐1H‐pyrazol‐3‐yl)phenyl)‐4,4,9,9‐tetramethyl‐4,4a,9,10a‐tetrahydro‐s‐indaceno[1,2‐b:5,6‐b′]dithiophen‐2‐yl)methylene)‐3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐yl)malononitrile (PR) and its derivatives P1–P7 were explored in this study. The compounds: PR and P1–P7 having donor–π–acceptor configurations and M06/6‐311G(d,p) functional was selected to inquire the dipole moment (μ), linear polarizability (α), first hyperpolarizability (β), and second hyperpolarizability (γ). The findings of perturbed Kohn–Sham relations were deciphered to derive charge density of the molecules. The optical analysis was performed in gaseous phase and their findings were observed in 544.2–697.1 nm range. Moreover, the natural bond orbitals, frontier molecular orbitals, density of state, and transition density matrices for the aforesaid compounds were also calculated at aforesaid level. Global reactivity parameters of PR and P1–P7 were analyzed by using highest occupied molecular orbital–lowest unoccupied molecular orbital energies. Overall, all above‐mentioned findings revealed significant optical nonlinear response in these pyrazoline‐based scaffold (PR and P1–P7). However, among all the compounds, P3 has shown the highest nonlinearity with maximum μtot, <α>, βtot, and γtot values at 19.4 D, 1.78 × 10−22, 2.57 × 10−27, and 3.13 × 10−32a.u., respectively. Hence, the current computational study might prove to be fruitful for the exploration of proficient NLO materials for optoelectronic devices. [ABSTRACT FROM AUTHOR]

First antibiotic in the oxazolidinone class, linezolid fights gram‐positive multiresistant bacteria by inhibiting protein synthesis through its interaction with the 50S subunit of the functional bacterial ribosome. For its antimicrobial action, it is necessary that its chiral carbon located in the oxazolidinone ring is in the S‐conformation. Computational calculation at time‐dependent density functional theory methodology, ultraviolet–visible (UV–Vis), and electronic circular dichroism spectra was obtained for noncomplexed and complexed forms of linezolid to verify the possible chirality of nitrogen atom in the acetamide group of the molecule. The molecular system has two chiral centers. So, there are now four possible configurations: RR, RS, SR, and SS. For a better understanding of the system, the electronic spectra at the PBE0/6‐311++G(3df,2p) level of theory were obtained. The complexed form was obtained from the crystallographic data of the ribosome, containing the S‐linezolid molecular system. The computational results obtained for the electronic properties are in good agreement with the experimental crystallographic data and available theoretical results. [ABSTRACT FROM AUTHOR]

The mechanism of aggregation-induced emission (AIE) for the bis(1-(2,4-difluorophenyl)-1H-pyrazole)(2-(20-hydroxyphenyl)-2-oxazoline)iridium(III) complex, denoted as Ir(dfppz)2(oz), was investigated with use DFT and the TD-DFT level of theory. The mechanism of radiationless deactivation of the triplet state was elucidated. Such a mechanism requires an additional, photophysical triplet channel of the internal conversion (IC) type, which is activated as a result of intramolecular motion deforming the structure of the oz ligand and distorting the iridium coordination sphere. Formally, the rotational movement of the oxazoline relative to the C–C bond in the oz ligand is the main active coordinate that leads to the opening of the triplet channel. The rotation of the oxazoline group and the elongation of the Ir-Nox bond cause a transition between the luminescent, low-lying triplet state with a d / π → π * characteristic ( T 1 (eq) ), and the radiationless d → d triplet state ( T 1 (Ir) ). This transition is made possible by the low energy barrier, which, based on calculations, was estimated at approximately 8.5 kcal/mol. Dimerization, or generally aggregation of the complex molecules, blocks the intramolecular movement in the ligand and is responsible for a strong increase in the energy barrier for the T 1 (eq) ⇝ T 1 (Ir) conversion of triplet states. Thus, the aggregation phenomenon blocks the nonradiative deactivation channel of the excited states and, consequently, contributes to directing the photophysical process toward phosphorescence. The mechanism involved in locking the nonradiative triplet path can be called restricted access to singlet–triplet crossing (RASTC). [ABSTRACT FROM AUTHOR]

The new design of 6,6′-di(thiophen-2-yl)-4,4′-bipyrimidine (DTB)-based organic dyes (TCIT1-TCIT6) for dye-sensitized solar cell (DSSC) application was systematically designed by a donor (D), π-linker, and acceptor (A) design to form the D-π-D-π-A structure. The exchange–correlation (XC) as well as long-range corrected (LC) functionals were utilized to represent these dyes in density functional theory (DFT) and time-dependent DFT (TD-DFT) techniques. The TD-CAM-B3LYP approach was perfectly matched the DTB dye. Energy gaps between highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) ranged between 1.73-2.92 eV. Their light-harvesting efficiency (LHE) values ranged between 0.001-0.106 eV with dye TCIT5 with the highest value. The open circuit voltage calculated against the DTB as donor moiety ranged 2.45–3.64 eV with positive values to demonstrate their ON position in their solar devices. All the dyes showed a very short excited-state lifetime ranging between 0.0001-0.0051 ns which showed how easily they can shift from an excited- (fluorescent) to ground-state position. Improved results for DSSCs were provided by the intended dyes in addition to their high horizontal dipole moment (µnormal) and open circuit photovoltage (eVOC). It benefits increased efficiency as a result. The findings of the current theoretical analysis show that all D-π-D-π-A dyes may be suitable sensitizers for DSSC applicability. [ABSTRACT FROM AUTHOR]

Due to their unique photophysical and electronic properties, pyrene and its analogues have been the subject of extensive research in recent decades. The propensity of pyrene and its derivatives to form excimers has found wide application in various fields. Nitrogen-substituted pyrene derivatives display similar photophysical properties, but for them, excimer emission has not been reported to date. Here, we use time-dependent density functional theory (TD-DFT) calculations to investigate the low-lying exciton states of dimers of pyrene and 2-azapyrene. The excimer equilibrium structures are determined and the contribution of charge transfer (CT) excitations and intermolecular interactions to the exciton states is disclosed using a diabatization procedure. The study reveals that the dimers formed by the two molecules have quite similar exciton-state patterns, in which the relevant CT contributions govern the formation of excimer states, along with the La/Lb state inversion. In contrast with pyrene, the dipole–dipole interactions in 2-azapyrene stabilize the dark eclipsed excimer structure and increase the barrier for conversion into a bright twisted excimer. It is suggested that these differences in the nitrogen-substituted derivative might influence the excimer emission properties. [ABSTRACT FROM AUTHOR]