Exploring the Sensing Potential of g-C3N4 versus Li/g-C3N4 Nanoflakes toward Hazardous Organic Volatiles: A DFT Simulation Study.

Ab initio calculations were performed to determine the sensing behavior of g-C3N4 and Li metal-doped g-C3N4 (Li/g-C3N4) quantum dots toward toxic compounds acetamide (AA), benzamide (BA), and their thio-analogues, namely, thioacetamide (TAA) and thiobenzamide (TAA). For optimization and interaction energies, the ωB97XD/6-31G(d,p) level of theory was used. Interaction energies (Eint) illustrate the high thermodynamic stabilities of the designed complexes due to the presence of the noncovalent interactions. The presence of electrostatic forces in some complexes is also observed. The observed trend of Eint in g-C3N4 complexes was BA > TAA > AA > TBA, while in Li/g-C3N4, the trend was BA > AA > TBA > TAA. The electronic properties were studied by frontier molecular orbital (FMO) and natural bond orbital analyses. According to FMO, lithium metal doping greatly enhanced the conductivity of the complexes by generating new HOMOs near the Fermi level. A significant amount of charge transfer was also observed in complexes, reflecting the increase in charge conductivity. NCI and QTAIM analyses evidenced the presence of significant noncovalent dispersion and electrostatic forces in Li/g-C3N4 and respective complexes. Charge decomposition analysis gave an idea of the transfer of charge density between quantum dots and analytes. Finally, TD-DFT explained the optical behavior of the reported complexes. The findings of this study suggested that both bare g-C3N4 and Li/g-C3N4 can effectively be used as atmospheric sensors having excellent adsorbing properties toward toxic analytes.

Theoretical Study of Dodecafluorophenylene-Based Superalkalides with Significantly High NLO Response.

Scientists are continuously trying to discover new approaches to develop materials with exceptional nonlinear optical responses. Compared with the single-ring Janus face compound (F6C6H6), the three-ring Janus face compound (C13H10F12) has a larger surface, where superalkali metals can be doped quite easily. Herein, the nonlinear optical response of Janus molecule dodecafluorophenylene (DDFP)-based superalkalides has been explored. The stability of the newly designed complexes is evident in the negative interaction energy values (ranging from -42.17 to -60.91 kcal/mol). The superalkalide nature of the complexes is corroborated through natural bond orbital (NBO) analysis, which shows negative charges on M3. This feature is further confirmed through frontier molecular orbital (FMO) analyses showing the highest occupied molecular orbital (HOMO) density over superalkalis (M3). The analysis also reveals that the H-L gap is reduced from 9.57 eV (for bare DDFP) to 2.11 eV for doped systems by adsorption of dopants on the DDFP surface. Moreover, the NLO response of the studied complexes is evaluated via static hyperpolarizabilities. The maximum value of first hyperpolarizability (ßo) among all of the designed compounds is for K3-DDFP-K3 (7.80 × 104 au) at M06-2X/6-31+G(d,p) level of theory. The ßo is also rationalized through a two-level model. Furthermore, for ßvec, the projection of hyperpolarizability on the dipole moment is calculated. The comparable results of ßvec and ßo indicate that the charge transfer in the complexes is parallel to the molecular dipole moments. These compounds, besides providing a new entry into excess-electron compounds, will also pave the way for the design and synthesis of further novel NLO materials.

Metallofullerenes as Robust Single-Atom Catalysts for Adsorption and Dissociation of Hydrogen Molecules: A Density Functional Study.

Hydrogen is currently considered as the best alternative for traditional fuels due to its sustainable and ecofriendly nature. Additionally, hydrogen dissociation is a critical step in almost all hydrogenation reactions, which is crucial in industrial chemical production. A cost-effective and efficient catalyst with favorable activity for this step is highly desirable. Herein, transition-metal-doped fullerene (TM@C60) complexes are designed and investigated as single-atom catalysts for the hydrogen splitting process. Interaction energy analysis (Eint) is also carried out to demonstrate the stability of designed TM@C60 metallofullerenes, which reveals that all the designed complexes have higher thermodynamic stability. Furthermore, among all the studied metallofullerenes, the best catalytic efficiency for hydrogen dissociation is seen for the Sc@C60 catalyst Ea = 0.13 eV followed by the V@C60 catalyst Ea = 0.19 eV. The hydrogen activation and dissociation processes over TM@C60 metallofullerenes is further elaborated by analyzing charge transfer via the natural bond orbital and electron density difference analyses. Additionally, quantum theory of atoms in molecule analysis is carried out to investigate the nature of interatomic interactions between hydrogen molecules and TMs@C60 metallofullerenes. Overall, results of the current study declare that the Sc@C60 catalyst can act as a low cost, highly efficient, and noble metal-free single-atom catalyst to efficiently catalyze hydrogen dissociation reaction.

Nonlinear Optical Properties and Phototunable Absorption of a Substituted Dihydroazulene-Vinylheptafulvene Pair of Photochromes.

Quantum calculations were used to study UV-vis absorption properties and nonlinear optical characteristics of a variety of substituted dihydroazulene (DHA)/vinylheptafulvene (VHF) photoswitches. The absorption properties are substantially based on the position and nature of the substituent. In general, electron-donating groups cause red shifts compared to the parent compound. Any electron-withdrawing group, on the other hand, would generate a blue shift. Furthermore, the steric effect at some positions is accountable for the loss of planarity and, as a response, a decrease in electronic conjugation within the molecule, which in most cases result in blue shifts in maximum absorption. The purpose of this research is to investigate the influence of substitution at the seven-membered ring of the DHA/VHF system on the absorption spectra and nonlinear optical characteristics of dihydroazulene photoswitches. UV-vis spectra and hyperpolarizability are determined since a prospective photoswitch should have a minimum overlap of absorption spectra from both isomers. Furthermore, the differential in hyperpolarizability between DHA and VHF is critical for practical applications.

Rational Design, Stabilities and Nonlinear Optical Properties of Non-Conventional Transition Metalides; New Entry into Nonlinear Optical Materials.

Electronic and nonlinear optical properties of endohedral metallofullerenes are presented. The endohedral metallofullerenes contain transition metal encapsulated in inorganic fullerenes X12Y12 (X = B, Al & Y = N, P). The endohedral metallofullerenes (endo-TM@X12Y12) possess quite interesting geometric and electronic properties, which are the function of the nature of the atom and the size of fullerene. NBO charge and frontier molecular orbital analyses reveal that the transition metal encapsulated Al12N12 fullerenes (endo-TM@Al12N12) are true metalides when the transition metals are Ni, Cu and Zn. Endo-Cr@Al12N12 and endo-Co@Al12N12 are at the borderline between metalides and electrides with predominantly electride characteristics. The other members of the series are excess electron systems, which offer interesting electronic and nonlinear optical properties. The diversity of nature possessed by endo-TM@Al12N12 is not prevalent for other fullerenes. Endo-TM@Al12P12 are true metalides when the transition metals are (Cr-Zn). HOMO-LUMO gaps (EH-L) are reduced significantly for these endohedral metallofullerenes, with a maximum percent decrease in EH-L of up to 70%. Many complexes show odd-even oscillating behavior for EH-L and dipole moments. Odd electron species contain large dipole moments and small EH-L, whereas even electron systems have the opposite behavior. Despite the decrease in EH-L, these systems show high kinetic and thermodynamic stabilities. The encapsulation of transition metals is a highly exergonic process. These endo-TM@X12Y12 possess remarkable nonlinear optical response in which the first hyperpolarizability reaches up to 2.79 × 105 au for endo-V@Al12N12. This study helps in the comparative analysis of the potential nonlinear optical responses of electrides, metalides and other excess electron systems. In general, the potential nonlinear optical response of electrides is higher than metalides but lower than those of simple excess electron compounds. The higher non-linear optical response and interesting electronic characteristics of endo-TM@Al12N12 complexes may be promising contenders for potential NLO applications.

Transition Metal-Doped C20 Fullerene-Based Single-Atom Catalysts with High Catalytic Activity for Hydrogen Dissociation Reaction.

Hydrogen dissociation is a key step in almost all hydrogenation reactions; therefore, an efficient and cost-effective catalyst with a favorable band structure for this step is highly desirable. In the current work, transition metal-based C20 (M@C20) complexes are designed and evaluated as single-atom catalysts (SACs) for hydrogen dissociation reaction (HDR). Interaction energy (E int) analysis reveals that all the M@C20 complexes are thermodynamically stable, whereas the highest stability is observed for the Ni@C20 complex (E int = -6.14 eV). Moreover, the best catalytic performance for H2 dissociation reaction is computed for the Zn@C20 catalyst (E ads = 0.53 eV) followed by Ti@C20 (E ads = 0.65 eV) and Sc@C20 (E ads = 0.76 eV) among all considered catalysts. QTAIM analyses reveal covalent or shared shell interactions in H2* + M@C20 systems, which promote the process of H2 dissociation over M@C20 complexes. NBO and EDD analyses declare that transfer of charge from the metal atom to the antibonding orbital of H2 causes dissociation of the H-H bond. Overall outcomes of this study reveal that the Zn@C20 catalyst can act as a highly efficient, low-cost, abundant, and precious metal-free SAC to effectively catalyze HDR.

Hydrogen Dissociation Reaction on First-Row Transition Metal Doped Nanobelts.

Zigzag molecular nanobelts have recently captured the interest of scientists because of their appealing aesthetic structures, intriguing chemical reactivities, and tantalizing features. In the current study, first-row transition metals supported on an H6-N3-belt[6]arene nanobelt are investigated for the electrocatalytic properties of these complexes for the hydrogen dissociation reaction (HDR). The interaction of the doped transition metal atom with the nanobelt is evaluated through interaction energy analysis, which reveals the significant thermodynamic stability of TM-doped nanobelt complexes. Electronic properties such as frontier molecular orbitals and natural bond orbitals analyses are also computed, to estimate the electronic perturbation upon doping. The highest reduction in the HOMO-LUMO energy gap compared to the bare nanobelt is seen in the case of the Zn@NB catalyst (4.76 eV). Furthermore, for the HDR reaction, the Sc@NB catalyst displays the best catalytic activity among the studied catalysts, with a hydrogen dissociation barrier of 0.13 eV, whereas the second-best catalytic activity is observed for the Zn@NB catalyst (0.36 eV). It is further found that multiple active sites, i.e., the presence of the metal atom and nitrogen atom moiety, help to facilitate the dissociation of the hydrogen molecule. These key findings of this study enhance the understanding of the relative stability, electronic features, and catalytic bindings of various TM@NB catalysts.

Covalent Triazine Framework C6N6 as an Electrochemical Sensor for Hydrogen-Containing Industrial Pollutants. A DFT Study.

Industrial pollutants pose a serious threat to ecosystems. Hence, there is a need to search for new efficient sensor materials for the detection of pollutants. In the current study, we explored the electrochemical sensing potential of a C6N6 sheet for H-containing industrial pollutants (HCN, H2S, NH3 and PH3) through DFT simulations. The adsorption of industrial pollutants over C6N6 occurs through physisorption, with adsorption energies ranging from -9.36 kcal/mol to -16.46 kcal/mol. The non-covalent interactions of analyte@C6N6 complexes are quantified by symmetry adapted perturbation theory (SAPT0), quantum theory of atoms in molecules (QTAIM) and non-covalent interaction (NCI) analyses. SAPT0 analyses show that electrostatic and dispersion forces play a dominant role in the stabilization of analytes over C6N6 sheets. Similarly, NCI and QTAIM analyses also verified the results of SAPT0 and interaction energy analyses. The electronic properties of analyte@C6N6 complexes are investigated by electron density difference (EDD), natural bond orbital analyses (NBO) and frontier molecular orbital analyses (FMO). Charge is transferred from the C6N6 sheet to HCN, H2S, NH3 and PH3. The highest exchange of charge is noted for H2S (-0.026 e-). The results of FMO analyses show that the interaction of all analytes results in changes in the EH-L gap of the C6N6 sheet. However, the highest decrease in the EH-L gap (2.58 eV) is observed for the NH3@C6N6 complex among all studied analyte@C6N6 complexes. The orbital density pattern shows that the HOMO density is completely concentrated on NH3, while the LUMO density is centred on the C6N6 surface. Such a type of electronic transition results in a significant change in the EH-L gap. Thus, it is concluded that C6N6 is highly selective towards NH3 compared to the other studied analytes.

Geometric, Electronic, and Optoelectronic Properties of Carbon-Based Polynuclear C3O[C(CN)2]2M3 (where M = Li, Na, and K) Clusters: A DFT Study.

Carbon-based polynuclear clusters are designed and investigated for geometric, electronic, and nonlinear optical (NLO) properties at the CAM-B3LYP/6-311++G(d,p) level of theory. Significant binding energies per atom (ranging from -162.4 to -160.0 kcal mol-1) indicate excellent thermodynamic stabilities of these polynuclear clusters. The frontier molecular orbital (FMOs) analysis indicates excess electron nature of the clusters with low ionization potential, suggesting that they are alkali-like. The decreased energy gaps (EH-L) with increased alkali metals size revael the improved electrical conductivity (σ). The total density of state (TDOS) study reveals the alkali metals' size-dependent electronic and conductive properties. The significant first and second hyperpolarizabilities are observed up to 5.78 × 103 and 5.55 × 106 au, respectively. The ßo response shows dependence on the size of alkali metals. Furthermore, the absorption study shows transparency of these clusters in the deep-UV, and absorptions are observed at longer wavelengths (redshifted). The optical gaps from TD-DFT are considerably smaller than those of HOMO-LUMO gaps. The significant scattering hyperpolarizability (ßHRS) value (1.62 × 104) is calculated for the C3 cluster, where octupolar contribution to ßHRS is 92%. The dynamic first hyperpolarizability ß(ω) is more pronounced for the EOPE effect at 532 nm, whereas SHG has notable values for second hyperpolarizability γ(ω).

Covalent Organic Framework (C6N6) as a Drug Delivery Platform for Fluorouracil to Treat Cancerous Cells: A DFT Study.

Continuous studies are being carried out to explore new methods and carrier surfaces for target drug delivery. Herein, we report the covalent triazine framework C6N6 as a drug delivery carrier for fluorouracil (FU) and nitrosourea (NU) anti-cancer drugs. FU and NU are physiosorbed on C6N6 with adsorption energies of -28.14 kcal/mol and -27.54 kcal/mol, respectively. The outcomes of the non-covalent index (NCI) and quantum theory of atoms in molecules (QTAIM) analyses reveal that the FU@C6N6 and NU@C6N6 complexes were stabilized through van der Waals interactions. Natural bond order (NBO) and electron density difference (EDD) analyses show an appreciable charge transfer from the drug and carrier. The FU@C6N6 complex had a higher charge transfer (-0.16 e-) compared to the NU@C6N6 complex (-0.02 e-). Frontier molecular orbital (FMO) analysis reveals that the adsorption of FU on C6N6 caused a more pronounced decrease in the HOMO-LUMO gap (EH-L) compared to that of NU. The results of the FMO analysis are consistent with the NBO and EDD analyses. The drug release mechanism was studied through dipole moments and pH effects. The highest decrease in adsorption energy was observed for the FU@C6N6 complex in an acidic medium, which indicates that FU can easily be off-loaded from the carrier (C6N6) to a target site because the cancerous cells have a low pH compared to a normal cell. Thus, it may be concluded that C6N6 possesses the therapeutic potential to act as a nanocarrier for FU to treat cancer. Furthermore, the current study will also provide motivation to the scientific community to explore new surfaces for drug delivery applications.

Phototunable Absorption and Nonlinear Optical Properties of Thermally Stable Dihydroazulene-Vinylheptafulvene Photochrome Pair.

The UV-vis absorption characteristics and nonlinear optical properties of a series of substituted dihydroazulene (DHA)/vinylheptafulvene (VHF) photoswitches are investigated by applying quantum calculations. Introduction of substituents at the seven-membered ring resulted in significant changes in their absorption properties depending on the nature and position of the substituent. Electron-donating groups at positions 5, 6, 7, and 8 generally exhibited red shifts with respect to the parent compound. However, the steric effect at positions 8a and 4 is responsible for the loss of planarity and conjugation, which generally leads to blue shifts. In contrast, any electron-withdrawing group, particularly at positions 8a and 4, would cause a blue shift. The presence of bulky groups at position 8a results in a loss of planarity and, as a result, a decrease in electronic conjugation within the molecule, resulting in a blue shift in the maximum absorption. When it comes to halogens, the red shift is directly correlated to the nucleophilicity; the higher the nucleophilicity, the larger the red shift. Regarding hyperpolarizability, the charge separation induces higher hyperpolarizabilities for all substituted VHFs compared to the corresponding DHAs, resulting in a much higher NLO response. In addition, for all DHA and VHF, the highest values of hyperpolarizabilities are calculated for 6-substituted systems. Finally, the objective of this detailed theoretical investigation is to continue exploring the photophysical properties of DHA-VHF through structural modifications.

Tuning Optical Properties of Chalcone Derivatives: A Computational Study.

The conformational feature of noncovalent complexes of two borondifluoride chalcone derivatives was assessed using DFT-D2. The corresponding optical properties were analyzed based on time-dependent density functional theory calculations. As already described in such complexes, the π-stacking interaction existing between both fragments allowed formation of a new absorption band corresponding to the S0 → S1 transition. However, this band appears very close to the most intense band corresponding the S0 → S2 transition.

Unraveling the performance of dispersion-corrected functionals for the accurate description of weakly bound natural polyphenols.

Long-range non-covalent interactions play a key role in the chemistry of natural polyphenols. We have previously proposed a description of supramolecular polyphenol complexes by the B3P86 density functional coupled with some corrections for dispersion. We couple here the B3P86 functional with the D3 correction for dispersion, assessing systematically the accuracy of the new B3P86-D3 model using for that the well-known S66, HB23, NCCE31, and S12L datasets for non-covalent interactions. Furthermore, the association energies of these complexes were carefully compared to those obtained by other dispersion-corrected functionals, such as B(3)LYP-D3, BP86-D3 or B3P86-NL. Finally, this set of models were also applied to a database composed of seven non-covalent polyphenol complexes of the most interest. Graphical abstract Weakly bound natural polyphenolsᅟ.

Synergism of antioxidant action of vitamins E, C and quercetin is related to formation of molecular associations in biomembranes.

Vitamins E, C and polyphenols (flavonoids and non-flavonoids) are major natural antioxidants capable of preventing damage generated by oxidative stress. Here we show the capacity of these antioxidants to form non-covalent association within lipid bilayers close to the membrane/cytosol interface. Antioxidant regeneration is significantly enhanced in these complexes.

Oligostilbenoids from the heartwood of N.†Heimii: role of non-covalent association in their biogenesis.

Four new oligostilbenes, including one dimer and three tetramers of resveratrol, that is, heimiols B-E (1-4) were isolated from the heartwood of Neobalanocarpus heimii (Dipterocarpaceae), together with thirteen known resveratrol oligomers (5-17). Examination of the structural diversity of the isolated oligostilbenes led to hypothesis of their biogenetic origin through a small number of versatile chemical pathways. These hypotheses are strongly supported by computational calculations (based on the density functional theory, DFT) that were performed to rationalize conformational re-arrangements and thus provide insights into the mechanism of oligostilbenoid biosynthesis. Non-covalent complexes are believed to drive the regio- and stereoselectivity of the oligomerization reactions.

Antioxidant properties of phenolic Schiff bases: structure-activity relationship and mechanism of action.

Phenolic Schiff bases are known for their diverse biological activities and ability to scavenge free radicals. To elucidate (1) the structure-antioxidant activity relationship of a series of thirty synthetic derivatives of 2-methoxybezohydrazide phenolic Schiff bases and (2) to determine the major mechanism involved in free radical scavenging, we used density functional theory calculations (B3P86/6-31+(d,p)) within polarizable continuum model. The results showed the importance of the bond dissociation enthalpies (BDEs) related to the first and second (BDEd) hydrogen atom transfer (intrinsic parameters) for rationalizing the antioxidant activity. In addition to the number of OH groups, the presence of a bromine substituent plays an interesting role in modulating the antioxidant activity. Theoretical thermodynamic and kinetic studies demonstrated that the free radical scavenging by these Schiff bases mainly proceeds through proton-coupled electron transfer rather than sequential proton loss electron transfer, the latter mechanism being only feasible at relatively high pH.