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We present in this paper the stability of SWCNT hybrid systems with Py molecules. vdW type interactions are therefore the main interaction mechanism between encapsulated molecules and nanotubes, and the simplest model to describe these interactions is the Lennard-Jones potential. We have therefore performed energy minimization calculations on hybrid SWCNTs in a very wide range of diameters and of all chirality using the Lennard-Jones potential. The structure of the carbon nanotube is obtained from the winding of graphene on itself to form a hollow cylinder described by the pair of integers (n, m) entirely determining its structural characteristics, while the optimization of the geometry of the Py molecule is obtained by SIESTA using the exchange–correlation functional LDA. After minimisation, an approach that combines density functional theory, molecular mechanics, bond polarizability model, and spectral moment's method has been used to compute Raman spectra. Two types of vibration modes of SWCNTs attract our attention. Initially, the modifications of the modes of Py after encapsulation will be analyzed. In the following discussion, we examine how the vibrational properties of single-walled carbon nanotubes (SWCNTs) are affected by encapsulation, specifically in relation to the RBM and tangential modes. Our analysis of the Raman active modes supports the notion that the structural integrity of the SWCNTs remains intact and indicates the occurrence of a charge transfer between the Py molecules and SWCNTs. This charge transfer depends on the geometric position of Py in the SWCNT. [ABSTRACT FROM AUTHOR]

The host–guest complexes formed between [9–11]CPPs and C60 were studied extensively due to their excellent photoelectric conversion properties and photochemistry. The drastically increased electron accepting ability of Li+@C60 with respect to C60 may induce strong intermolecular charge transfer interaction with [9–11]CPP. In this paper, a comprehensive computational analysis of the structure, intermolecular interactions, absorption spectra, charge transfer characteristics and nonlinear optical properties of [9–11]CPP⊂C60 and [9–11]CPP⊂Li+@C60 were studied using density functional theory calculations. It was found that the intermolecular binding energies of [10]CPP⊂C60 and [10]CPP⊂Li+@C60 were −47.76 and −60.08 kcal mol−1, which were larger than those of [9, 11]CPP⊂C60 and [9, 11]CPP⊂Li+@C60. Thus, [10]CPP was found to be the most ideal fullerene encapsulator and most suitable for encapsulating C60. In addition, with the increase of the CPP ring size, the second hyperpolarizability (γ) values of [n]CPP⊂C60 increase gradually. In addition, the γ values of [9–11]CPP⊂Li+@C60 were all greater than those of [9–11]CPP⊂C60, indicating that embedding Li+ into fullerene spheres can effectively improve their third-order nonlinear optical responses. [ABSTRACT FROM AUTHOR]

In this paper, eight complexes M-1, M-2, M-3 and M-4 (M = Ir or Rh) in the general formula [M(C^N)2(N^N)] (C^N = cyclometalated ligands and N^N = ancillary ligands) are systematically investigated by density functional theory (DFT) and time-dependent DFT methods. With the aim to study the influence of metal centers for nonlinear optical (NLO) responses, the geometrical and electronic structures, first hyperpolarizabilities (βtot) and UV-Vis absorption spectra are investigated in detail. It is found that the βtot values increase 1.8–3.7 times as the metal atom changes from Rh to Ir. Among all the studied complexes, Ir-3 (C^N = 4-chloro-2-phenylquinoline with N^N = 2,9-dimethyl-1,10-phenanthroline) shows the highest βtot value with an amplitude of 2415.4 a.u. computed at the ωB97XD/6-31G+(d)/SDD level, which can be seen as a promising candidate for second-order NLO materials. In addition, the HOMO energy levels increase upon increasing the size of the metal atom, which contributes to a significant reduction in HOMO–LUMO gaps. The βtot values and HOMO–LUMO gaps are in an inverse relationship. Furthermore, tuning the center metals Ir/Rh can be seen as an effective method to modulate the charge transfer degree. We anticipate that this study may serve as a new strategy for the rational design and synthesis of second-order NLO materials. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) calculations have been carried out to investigate two synthesized iridium(III) complexes with substituted Phbd (1-phenyl-2-(pyridin-2-yl)-1H-benzo[d]imidazole) and Crbd (9-(4-(2-(pyridin-2-yl)-1H-benzo[d]imidazol-1-yl)phenyl)-9H-carbazole) as ancillary ligands. The aim of this paper is to study the effect of the substituent on the geometrical structures, electronic and second-order nonlinear optical (NLO) properties, and UV-vis absorption spectra. It is found that the first hyperpolarizabilities can be easily modulated by the introduction of Phbd and Crbd units. The complex with Phbd possesses larger first hyperpolarizability values compared to the complex with Crbd as an ancillary ligand. Significantly, the changes in the first hyperpolarizabilities can be qualitatively explained by means of the charge transfer pattern. It is anticipated that the theoretical investigation of these iridium(III) complexes will be helpful for designing high performance and versatile NLO materials. [ABSTRACT FROM AUTHOR]

In this work, particle swarm optimization (CALYPSO) is combined with density functional theory (DFT) to perform a comprehensive structure search for the Bn0/−Rb2 (n = 1–12) clusters. The ground-state structures of the Bn0/−Rb2 (n = 1–12) clusters were determined based on the total energy of the obtained structures. It was also found that when the number of B atoms was low, the doped cluster geometry mainly behaved as planar or planar-like. The addition of doped Rb atoms distorts the boron clusters, with the doping position around the main body of boron. The stability analysis shows that the B8Rb2 cluster with a double pyramidal structure and a symmetry of D7h has excellent stability in the studied system. The energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital is 6.14 eV. Bonding analysis is performed using molecular orbitals and density of states, and the results show that strong communications between the two Rb atoms and the B-atom bulk dominate their significant stability, where mainly the p atom orbital of the Rb atoms interacts with the s and p atom orbitals of the B atoms. Furthermore, the bond level density and naturally adapted orbital analysis revealed that the formation of effective π-type naturally adapted orbitals between the doped Rb atoms and the B atoms, with a higher delocalization index, is one of the reasons for the higher cluster stability. [ABSTRACT FROM AUTHOR]

Carbon nanohoop compounds have attracted extensive attention recently due to their aesthetically pleasing structures and unique properties. In order to reveal the structure–property relationship between the size-dependent effect and the nonlinear optical (NLO) response, a series of carbon nanohoops consisting of zigzag carbon nanotubes (CNTs), named D-CM2PnP-A (n = 4, 6, 8, 10, and 12), are systematically designed and investigated using density functional theory (DFT). Significantly, the first hyperpolarizability (βtot) of the system increases with the increasing structure size, which is primarily the result of the charge transfer transition. Subsequently, the major electronic transition changes from local excitation to charge transfer as the size of the structure increases, indicating that charge transfer becomes stronger significantly. Furthermore, a two-level model and the absorption spectrum can well explain the trend of the βtot value. In addition, the unit sphere representation (USR) and hyper-Rayleigh scattering (HRS) are used to further explain the nature of the second-order NLO response. More importantly, adding a π-bridge as an effective strategy further enhances the second-order NLO responses of the system. The relevant results are expected to provide a new perspective on the structure–NLO property correlation of donor (D)–conjugated bridge (π)–acceptor (A) type carbon nanohoops and theoretical guidance for the rational design and synthesis of fascinating carbon nanohoops as NLO materials. [ABSTRACT FROM AUTHOR]

A series of cyclometalated Ir(III) complexes possessing the general formula of [Ir(pqe)2(S^N)], pqe = 2-phenyl-quinoline-4-carboxylic acid methyl ester, S^N = pyridine-2-thiolate (Spy, B1); pyrimidine-2-thiolate (SpyN, B2); 5-(trifluoromethyl)-pyridine-2-thiolate (SpyCF3, B3); 2-thiazoline-2-thiolate (Stz, B4) and benzothiazole-2-thiolate (SBt, B5), were synthesized and characterized using several spectroscopies and analytical techniques. These compounds were photophysically investigated using UV-Vis absorption and photoluminescence spectroscopies. The complexes demonstrate strong red emissions in their CH2Cl2 solutions at 298 K but with different quantum efficiencies (B3 > B2 > B1 > B5 > B4). The emissions majorly originate from a 3MLCT (metal to ligand charge transfer) character along with smaller contributions of 3ILCT (intra ligand charge transfer) and 3L′LCT (ligand to ligand charge transfer; L = pqe, L′ = S^N). The esteric functional group (COOMe) on the pqe ligand can be easily converted to COO−Na+ in a hydrolysis process, resulting in the corresponding complexes [Na2{Ir(pqc)2(S^N)}], S^N = Spy, C1; SpyN, C2; SpyCF3, C3, being very water-soluble. Based on this hydrolysis, a large blue-shift is observed for the emissions of C1–C3 compared to B1–B5 which is supported by density functional theory (DFT) calculations. Also, the emission intensity of these complexes is sensitive to pH and steadily increases with the pH of solutions. The lifetime values as the other function of emission is changed by varying the pH values, wherein the graphs of lifetime/pH become quasi-linear. The slopes of the lines, as an index for the pH-sensitivity property, demonstrate the trend of C3 > C2 > C1 for the pH sensitivity of the complexes. [ABSTRACT FROM AUTHOR]

Molybdenum disulfide (MoS2)-based transition-metal chalcogenides are considered to be cost-efficient, environmentally-friendly, and stable materials in the application of electrocatalytic hydrogen production. However, the low density and poor reactivity of active sites within the basal plane of MoS2 hinder hydrogen evolution reaction (HER). Herein, we reported that N, P co-doped in the basal plane of MoS2 (N, P-MoS2) can convert the parts of 2H MoS2 to 1T MoS2 and enlarge interlayer spacing for an efficient HER. Subsequently, electrochemical tests revealed that N, P-MoS2 showed an overpotential of 179 mV at 10 mA cm−2, a corresponding Tafel slope of 143 mV dec−1, and remarkable long-term stability over 20 h. In addition, we combined these findings with theoretical results from density functional theory (DFT) simulations. The results confirmed that the synergistic effect of N and P activated the HER catalytic activity at the edge of N-MoS2. In short, the synergy improved the conductivity of N-MoS2 and promoted the rapid transfer of charge to achieve high-performance HER activity. The work provides new insight into the synergistic effect of N and P co-doped in the basal plane of MoS2, as well as a new pathway for the rational design of efficient HER electrocatalysts. [ABSTRACT FROM AUTHOR]

In the present work, the interaction between the B12N12, B12N12-16Hm, B23N5 and B47N53 fullerenes and lauric acid is analyzed. We perform in silico calculations at the Kohn–Sham scheme within the framework of density functional theory using the HSEh1PBE/6-31G(d) level of theory, in order to evaluate the adsorption of lauric acid on neutral [B12N12 (pristine), B12N12-16Hm (Hm = homonuclear bonds), and B47N53] and anionic fullerenes [B23N5]. The neutral systems present adsorption energy values in the range from −0.98 eV up to −2.26 eV, indicating a chemisorption generated between the oxygen atom of the lauric acid and a boron of the fullerenes. According to the quantum parameters, most systems are stable and could improve their solubility when complexes are formed with lauric acid. Also, the whole set of systems exhibits re-distribution and transfer of charge, which helps to stabilize them. In general, B12N12, B12N12-16Hm, and B47N53g present good performance to adsorb lauric acid, and they may be proposed as nanovehicles to transport this particular molecule in biological applications and so on. [ABSTRACT FROM AUTHOR]

The feasibility of the formation of sandwich and multidecker complexes between O2 molecules and alkali/alkaline earth metals has been analyzed in the light of density functional theory (DFT). The high value of the stabilization energy (SE) confirmed strong interactions in such sandwich and multidecker complexes. The total SE of the complexes increases with increase in the size of the complexes, and the average SE exhibits an opposite trend to that of the total SE. The solvent phase results indicate even stronger complexation upon the incorporation of a dielectric solvent. NBO analysis indicated charge transfer upon complexation from the metal to the antibonding π-orbital of O2. The interaction can be assumed to be primarily covalent in nature, and the process of complexation is thermodynamically favourable. TD-DFT calculations showed a red shift in the absorption maxima upon complexation, which indicates the ability to absorb more in the visible region. [ABSTRACT FROM AUTHOR]

Generation of molecular hydrogen by electrochemical water splitting is a promising approach, and its efficiency strictly depends on the electrocatalyst used. Therefore, it is an ongoing challenge to design materials having improved the electrocatalytic behaviour towards hydrogen evolution reaction. Here, using Co-MOF [Co4(BTC)3(BIm)6] as starting precursor, graphitic carbon encapsulated CoSe2 nanorods have been prepared through a single step selenization method. The carbon network in the CoSe2/C hybrid nanostructure forms channels, facilitating the accessibility of the electrolyte ions and maximizing the utilization of catalytic active centers. This makes the hybrid to show higher electrochemical accessible surface area, lower charge transfer resistance, and improved catalytic durability towards the electrocatalytic hydrogen evolution reaction with respect to the non-noble metal (graphite rod) counter electrode. Specifically, it needs only 253 mV of overpotential to reach the benchmarked current density (10 mA cm−2) with a lower Tafel slope. Further, the experimental findings have been supported by the theoretical analysis of the structure and electronic properties of CoSe2 and CoSe2/C hybrid by density functional theory (DFT) simulations. The interaction between CoSe2 and C is due to charge transfer from Co 3d orbital and Se 4p orbital of CoSe2 to the 2p orbital of carbon. Also, populated electronic states near Fermi level for C doped CoSe2 may infer towards increased conductivity of the material. Computed overpotentials for HER activities show a qualitative order of CoSe2/C < CoSe2, matching nicely with the experimental data. The synergic effect of increased conductivity, improved surface area, and superior electrocatalytic activity due to C doping is responsible for the superior HER catalytic performance. [ABSTRACT FROM AUTHOR]

The photoelectrocatalytic performance of (Sb,N)–MnO2 is explored by experiment and first principles calculation based on density functional theory. The photoelectrochemical performance test shows that 6% (Sb,N)–MnO2 with a maximum electrochemically active area and minimum charge transfer resistance has an oxygen evolution potential of 1.59 V. At this ratio, the photocurrent density reaches 8.00 mA cm−2 and the degradation rate is 87.89%. Furthermore, the possible role of Sb and N doping in modifying the photoelectrocatalytic performance is studied theoretically. The band gap decreases from 0.944 eV to 0.203 eV due to the formation of the charge compensation effect, which is conducive to the photoelectrocatalytic performance. The theoretical predictions agree well with the experimental results, which can provide an ideal alternative material for wastewater treatment. [ABSTRACT FROM AUTHOR]

In this work, based on the N-phenyl carbazole fluorescent group, a new molecule named 2-(4-(9-phenyl-9H-carbazol-3-yl)benzylidene)-1H-indene-1,3(2H)-dione (PCBI) is firstly synthesized and used as a fluorescent probe for detecting N2H4 in aqueous solutions. The PCBI probe exhibits an excellent aggregation-induced emission (AIE) effect with a good fluorescence response to N2H4 in a DMF–H2O (fw = 90%) system. A fitting curve between the fluorescence intensity at 628 nm of probe and the concentration of N2H4 shows excellent linear in the range of 0–6 × 10−6 mol L−1. Meanwhile, the PCBI probe exhibits good sensitivity and selectivity. Based on the density functional theory, the sensing mechanism of this probe is attributed to a change of the molecular aggregation state and an induced charge transfer (ICT) effect from group conversion. The PCBI test strip can be applied successfully to detect N2H4 rapidly in water. [ABSTRACT FROM AUTHOR]

The structural stability of carbon and the high theoretical capacity of silicon was the motivation for investigating the prospects of layered silicon carbide (SiC). The density functional theory (DFT) based computations and first-principles molecular dynamics (MD) simulations were performed to determine the likelihood of being able to use 2D SiC layers as a lithium intercalation compound. The calculations were performed using dispersion corrected exchange correlation and this revealed the stability of the layers, and the transfer of charge from Li to the host during intercalation was at a maximum storage capacity of 699 mA h g−1. The layers offered better flexibility, a higher rate capability and a three times larger capacity when compared to graphite bilayers. The diffusion barrier calculated here, with a small energy barrier of 0.40 eV, illustrated a good rate capability. The findings and comparison with graphite revealed that layered SiC is an appropriate anode material for used in lithium ion batteries (LIBs) because of its structural firmness, high electronic conductivity, low diffusion barrier and high storage capacity. [ABSTRACT FROM AUTHOR]

Two novel complexes were constructed by adsorption of two typical organic molecules, including one electron-donating molecule (TTF = tetrathiafulvalene) and one electron-withdrawing molecule (TCNQ = tetracyanoquinodimethane), on the surface of black phosphorus quantum dots (BPQDs). There exist considerable charge transfer and strong non-covalent interaction between organic molecules and BPQDs. The results of density functional theory (DFT) calculations show that the static first and second hyperpolarizabilities can be significantly enhanced by introducing TTF/TCNQ groups on BPQDs. Apart from static nonlinearity, hyper-Rayleigh scattering (HRS) first hyperpolarizability shows a remarkable value at a dispersion frequency of 1907 nm. Besides, the frequency-dependent first hyperpolarizability increases significantly while going from the gas to solvent phase. BPQDs–TTF presents a strong dipolar character, whereas BPQDs–TCNQ presents a relatively larger octupolar behavior. Compared with BPQDs–TTF, BPQDs–TCNQ exhibits better stability and larger first hyperpolarizability. This work highlights the superiority of combining TCNQ and BPQDs to construct high-performance nonlinear optical (NLO) molecules. [ABSTRACT FROM AUTHOR]

The electrochemical nitrogen reduction reaction (NRR) is currently the most attractive method for ammonia production, in which the development of high efficiency and low-cost electrocatalysts is still a challenge. A lot of recent research has been focused on B single-atom catalysts. However, doping carbon materials with multiple hetero-elements has been rarely explored. Herein, we investigate the catalytic performance of B doped, N doped, and BN co-doped defective graphdiyne (B@GDY, N@GDY and BN@GDY) for nitrogen reduction by using density functional theory. Our results reveal that BN@GDY exhibits higher catalytic efficiency relative to that of single B doping, which is manifested by a significant decrease in overpotential (0.32 V vs. 0.61 V) via the enzymatic mechanism. The projected density of states and Bader charge analysis indicate that BN@GDY can promote the charge transfer from the catalytic substrate to adsorbed N2, in which the addition of N can convert B from sp2 to sp3 hybridization. Meanwhile, the competing hydrogen evolution reaction (HER) can be well inhibited during the NRR for both B/BN@GDY substrates, especially in BN@GDY, indicating the high selectivity of BN@GDY towards the NRR. Above all, this work puts forward a novel metal-free electrocatalyst for the NRR and may provide useful guidance for the design of new non-metal nitrogen reduction electrocatalysts. [ABSTRACT FROM AUTHOR]

A novel fluorescent sensor (LJ-1) as a Zn2+ and nitro oxide (NO) relay recognition probe was designed and synthesized based on the aminomethylnaphthol moiety. In PBS buffer, LJ-1 showed high selectivity and ratiometric fluorescence response to Zn2+ on the basis of the intermolecular charge transfer (ICT) mechanism. Spectroscopic titrations showed that LJ-1 could be recognized as a fluorescent turn-on probe with a 10−8 M detection level. Subsequently, the resultant LJ–Zn2+ complex could act as a turn-off probe for the detection of NO in several seconds at the 10−8 M detection level. Furthermore, the binding modes of Zn2+ and NO with LJ-1 were elucidated by a computational study using density functional theory (DFT). The results demonstrated that LJ-1 can serve as a ratiometric fluorescent probe for relay recognition of Zn2+ and NO in an aqueous medium at physiological pH value. [ABSTRACT FROM AUTHOR]

A hot exciton model is a widely accepted mechanism for the generation of photocurrent in organic bulk-heterojunction solar cells, in which the charge is transferred from the high-energy Frenkel exciton state (FE state) of the donor to the low-energy charge transfer states (CT states) and then is further separated into free charges. However, the FE state energy of the acceptor (FEA state) is usually lower than the values of CT states, which could hinder the pathway of efficient charge transfer from the FEA state to CT states. In order to take full advantage of this pathway, in this study, acceptor molecule 1 which breaks the Kasha's rule was selected to constitute the donor/acceptor (D/A) interface with donor molecule PTB7-Th. The density functional theory (DFT) and the time-dependent density functional theory (TD-DFT) calculations focusing on the charge transfer mechanism were carried out to verify our supposition. The results indeed show higher energy in the FEA state than the lowest CT states and enhanced charge transfer contribution (about 90%), which implies the realization of this additional pathway. Meanwhile, based on acceptor molecule 1, molecules 2–6 were designed by introducing different functional groups with the aim of enhancing the open circuit voltage (VOC) and photo-absorption ability while maintaining the advantage of the higher FE state energy, which demonstrates the improvement in hole and electron generation efficiency to some extent. Therefore, this study may provide a good strategy for designing new non-fullerene acceptors for organic solar cells (OSCs). [ABSTRACT FROM AUTHOR]

While a plenty of work has been done on metal complexes incorporating N- and O-functionalised dicarboxylic acids (iminodiacetic acid and oxydiacetic acid, respectively), S-functionalised dicarboxylic acid, i.e. thiodiglycolic acid (H2tdga), is less explored and requires attention. In this study, two dinuclear complexes, namely [Mn2(tdga)2(phen)2]·2CH3OH (1) and [Cu2(tdga)2(phen)2]·H2tdga (2), were characterised employing spectral, single-crystal X-ray diffraction and DFT/TD-DFT studies. Time-dependent density functional theory (TD-DFT) reveals the types of electronic transition between metal-to-ligand charge transfer (MLCT) and intra-ligand charge transfer (ILCT). The crystal structure reveals the presence of various non-covalent interactions, which are further corroborated from Hirshfeld surface analysis. In EPR spectral analysis, 1 shows an isotropic signal at g = 1.99 due to Mn2+ (d5) with ground-state term 6S having a six-coordinate distorted octahedral geometry, while 2 shows two resonances, namely, g‖ = 2.21 and g⊥ = 2.11 due to the Jahn–Teller distortion of Cu2+ (d9) ions. The anisotropic g values are in the order of g‖ > g⊥ > 2.0, which is characteristic of an axially elongated tetragonal distortion with a dx2–y2 ground-state energy level. Assessment of catecholase-like activity provides Kcat = 962.56 (h−1) for 2, indicating enhanced enzymatic activity of 2 towards the oxidation of catechol (3,5-DTBC) to a quinone derivative (3,5-DTBQ). The catecholase activity of 2 is also corroborated by density functional theory (DFT) analysis. [ABSTRACT FROM AUTHOR]

Quantum chemical calculations at both density functional theory (DFT) and single-point CCSD(T) levels suggest that Be2B6 (D6h, 3A1g) and Be2B7+ (D7h, 3A2′) clusters adopt interesting inverse sandwich structures with spin-triplet ground states, featuring a perfect planar B6 (or B7) monocyclic boron ring being sandwiched by two lone Be atoms. There is pronounced charge transfer from the Be atoms to the monocyclic boron rings, leading to [Be]2+[B6]4−[Be]2+ and [Be]2+[B7]3−[Be]2+ charge transfer complexes. Chemical bonding analysis showed that Be2B6 and Be2B7+ clusters have σ/π double aromaticity with 4σ and 6π delocalized electrons on the boron rings. The Be2B6 inverse sandwich possesses the smallest monocyclic boron ring motif in Be-doped boron clusters to date. [ABSTRACT FROM AUTHOR]

Linear conducting polymers are extensively studied as sensors for various analytes, whereas studies on cyclic analogues are limited. In this study, sensor applications of cyclic oligothiophenes (nCTs) have been explored by means of DFT (density functional theory) calculations. Three models, namely, five (5CT)-, six (6CT)- and seven (7CT)-membered cyclic oligothiophenes are evaluated against twelve different gaseous analytes. For optimization of geometries and interaction energies, the B3LYP method including Grimme's dispersion correction (B3LYP-D3) was applied with the 6-31++G(d,p) basis set. Chemical interactions of nCTs with NH3, CO, CO2, N2H4, HCN, H2O2, H2S, CH4, CH3OH, SO2, SO3 and H2O analytes are analyzed via interaction energies, Gibbs free energies, electronic properties and UV-Vis analysis. The interaction energies are quantitatively correlated with the volume of the cyclic oligothiophene (nCT). The electronic properties are calculated at the widely accepted B3LYP/6-31G(d) level of theory; however, the TD-B3LYP/6-31G(d) method is used for the UV-Vis analysis. Symmetry-adapted perturbation theory reveals that the 5CT system is highly sensitive towards analytes as compared to the 6CT and 7CT systems. This assumption is also strengthened by the HOMO–LUMO gaps and excited state properties. ESAPT, HOMO–LUMO gaps, NCI, and NBO charge transfer suggest that nCTs are highly sensitive towards SO3 followed by SO2. The density of state spectra shows the reasonable variation in the peaks of nCTs upon interaction with SO2 and SO3 analytes. The findings of this study suggest that cyclic oligothiophenes can effectively be used for the rational design of atmospheric sensors, which are superior to the conventional sensors. [ABSTRACT FROM AUTHOR]

Focusing on the remarkably various cyclometalated Pt(ii) acetylcetonate complexes bearing an isomeric donor (D)–acceptor (A) conjugation framework ligand by virtue of adjusting the nitrogen atom coordination position, we have systematically investigated the geometric and electronic structures, redox properties, polarizabilities, first hyperpolarizabilities (βtot), and first hyperpolarizability densities of these intriguing isomeric Pt(ii) complexes using density functional theory with the view to rationalizing the nonlinear optical (NLO) structure–function relationships. Our calculations demonstrated that modulating the coordination position that affects the intramolecular D–A interactions gives rise to large second-order NLO responses in the studied complexes, which are qualitatively elucidated in terms of the change in the charge transfer (CT) patterns using time-dependent density functional theory. In particular, for complex 2, coordination with the stronger electron donating capacity of triphenylamine and the electron-withdrawing ability of the [1,2,5]thiadiazolo[3,4-c]pyridine unit produces the highest βtot value (329 × 10−30 esu) owing to the obvious bidirectional CT transition, which is the most fascinating candidate for a NLO material among all of the investigated complexes. Significantly, a noteworthy finding was that remarkable βtot contrasts were observed for these isomeric Pt(ii) complexes upon redox process, illustrating that they could be applicable for efficient redox-triggered NLO switches, especially using an oxidation stimulus with the highest on/off ratio, approaching 168.6 for complex 3. Furthermore, we have also quantitatively investigated the solid-state polarization effects on the βtot values for neutral complexes using the polarizable continuum model. Therefore, it can be anticipated that the present work may be advantageous to the experimental and theoretical design of novel smart cyclometalated Pt(ii) complexes for functional NLO materials. [ABSTRACT FROM AUTHOR]

The charge transport properties of a series of tetraazapyrene derivatives are theoretically investigated by means of quantum chemical calculations based on density functional theory. The effect of modifying the molecular structures on the charge transport properties is explained with quantitative Kohn–Sham molecular orbital analyses and corresponding energy decomposition analyses of the intermolecular interactions. The results reveal that the charge transfer does not depend on the substituent groups, such as the introduction of electron-attracting groups. Nevertheless, there is crucial evidence that the extension of the main chain and the increase in the number of heterocycles strengthen charge transfer in the systems. 3D visual diagrams of the anisotropy of the charge mobility in two different crystalline models of the same molecule are used to estimate the effect of molecular stacking motifs on the charge transfer properties. The maximum mobility is considered to be along the direction that is perpendicular to the molecular π–π stacking layers with the largest transfer integral values. In addition, spectral analyses of the polyheterocyclic derivatives provide novel conclusions about the effect of the molecular structures on the photophysical properties. [ABSTRACT FROM AUTHOR]

The charge transfer complexes of the donor 4-isopropyl-2-benzyl-1,2,5-thiadiazolidin-3-one1,1-dioxide (SF) with π acceptors 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and tetracyanoethylene (TCNE) have been studied spectrophotometrically in chloroform and methanol at room temperature. The results indicated the formation of CT-complexes with a molar ratio of 1 : 1 between donor and each acceptor. The physical parameters of the CT-complexes were evaluated using the Benesi–Hildebrand equation. The data were analyzed in terms of their stability constant (K), molar extinction coefficient (εCT), thermodynamic standard reaction quantities (ΔG0, ΔH0, ΔS0), oscillator strength (f), transition dipole moment (μEN) and ionization potential (ID). The experimental studies were complemented by quantum chemical calculations by the time-dependent density functional theory (TD-DFT) at the B3LYP level. The theoretical UV visible and FT-IR spectra were compared with those obtained experimentally. The first order hyperpolarizability (β0) and related properties (α0 and Δα) are calculated using the B3LYP method on the finite-field approach. The Mulliken charges, MEP calculations, the electronic properties, HOMO and LUMO energies and NBO analysis were performed on an optimized charge transfer complex of SF-DDQ. [ABSTRACT FROM AUTHOR]

We have designed three dimensional conjugated three- and four-armed molecules for organic solar cells, featuring a bithiophene donor (DF) fragment connected to a pyridine-thiadiazole acceptor fragment (AF) via an ethyne π-spacer (Ps) as the arms, which are linked to different central core atoms (N, B, C and Si atoms) based on two topologies, “core-D–π–A” (molecules are named N3-Mol, B3-Mol, Si4-Mol and C4-Mol) and “core-A–π–D” (molecules are named N3-RMol, B3-RMol, Si4-RMol and C4-RMol). A combination of density functional theory (DFT) and time-dependent-DFT (TD-DFT) approaches is applied to understand the effect of different central cores on the optical, electronic and charge transport properties of the two topologies. The “core-A–π–D” type molecules display smaller Eg values than those of the “core-D–π–A” type molecules. Therefore, the “core-A–π–D” type molecules show a significant red shift in λmax compared to the “core-D–π–A” type molecules. The molecules C4-RMol, Si4-RMol, B3-RMol and N3-RMol show red shifts of 59, 14, 28 and 39 nm in λmax as compared to C4-Mol, Si4-Mol, B3-Mol and N3-Mol, respectively. Three-armed N3-Mol and N3-RMol display the largest λmax of the designed molecules. Interestingly, B3-RMol and C4-RMol show more or less same λmax values. However, B and Si cores also show more intense absorption bands than N and C cores, respectively. Both the reorganization energy and mobility results reveal that the four-armed molecules show higher charge transport rates than the three-armed molecules because of their better dimensionality. N3-RMol exhibits μe and μh mobilities of up to 2.8 × 10−2 cm2 V−1 s−1 and 3.3 × 10−2 cm2 V−1 s−1 respectively while C4-RMol shows higher μe and μh mobilities of up to 0.163 cm2 V−1 s−1 and 4.14 × 10−2 cm2 V−1 s−1 respectively in the crystalline state, which have been predicted using the P21/c space group. Thus, the comparative analysis of the designed molecules reveals that the “core-A–π–D” topology with the substitution of N and C cores results in molecules which exhibit a narrow Eg, broad and intense absorptions and an anisotropic high charge carrier mobility in the crystalline phase, which is associated with low reorganization energies for organic solar cells. [ABSTRACT FROM AUTHOR]

Hexagonal boron nitride (h-BN) has attracted extensive attention due to its broad applications in electronic devices. Among various methods, the chemical vapor deposition (CVD) method has the most potential for obtaining high-quality h-BN films. A deep understanding of the initial nucleation process is essential for the rationally designed synthesis of h-BN. In this work, we systematically studied the stabilities of various BN clusters on Ru(0001) and Rh(111) surfaces by density functional theory simulations. Our results show that geometry types, docking sites, edged atoms, symmetry of geometries, and metal substrates can influence the stabilities of BN clusters. A structure crossover from a chain-like to the sp2 honeycomb geometry occurs at a critical size of 6 on both metal surfaces. After this, the honeycomb geometry is the energy-favoured one and down-hill growth continues until full coverage of h-BN is reached. The nucleation of h-BN is an energy-driven process governed by the charge transfer between BN clusters and underlying metals. The atomic scale understanding should provide helpful information on the rationally designed synthesis of h-BN and other binary 2D materials. [ABSTRACT FROM AUTHOR]

A new series of luminescent phosphine copper(I) complexes with cyano- and hydroxyl-substituted 2,2′-bipyridine ligands [CuI(bpy(CN)2)(P(PhX)3)2](ClO4) [X = H (1); Me (2); Cl (3)], [CuI(bpy(CN)2)(POP)](ClO4) (4), [CuI(bpy(OH)2)(PPh3)2](ClO4) (5) and [CuI(bpy(OH)2)(POP)](ClO4) (6) have been synthesized and characterized. Three of these complexes have been structurally characterized by using X-ray crystallography. The effect of the attaching –CN and –OH groups at the ortho-positions of bpy ligand was investigated. In CH2Cl2 solution, these complexes show yellow to orange phosphorescence, with the emission maxima not only sensitive to the electronic nature of the bipyridine ligands, but also considerably varied with the modification of phosphine ligands. In addition, these complexes show intense tunable green to yellow emissions in their solid state. To elucidate the electronic structures and transitions of these complexes, density functional theory (DFT) calculations on representative examples revealed that the lowest energy electronic transition associated with these complexes predominantly originates from metal-to-ligand charge transfer transitions (MLCT). [ABSTRACT FROM AUTHOR]

Monolayered carbon phosphide (CP), with semi-metallic electrical conductivity and graphene-like Dirac cone responses, has attracted significant attention from the advanced nanoelectronics community, for use in gas sensing devices. The CP monolayer exhibits semi-metallic behavior in the x-direction and semi-conducting behavior in the y-direction. With the presence of graphene-like Dirac cones, it holds highly anisotropic carrier mobility characteristics. Here, we introduce the first-principle theoretical calculations for understanding the adsorption mechanism of different gas molecules – CO, CO2, NH3, NO and NO2 – on the monolayer for electronic sensing devices. The binding strengths of these gas molecules adsorbed on the CP layer are much stronger than for other reported two-dimensional materials, such as graphene, blue phosphorene, germanene, etc. Additionally, the charge transfer analysis also supported an enhanced binding strength due to the sufficient amount of charge sharing between the CP monolayer and gas molecules. We further present an extensive study about the transport properties of CP monolayer sensor devices with electrodes made out of identical materials. The transmission characteristics, the density of states, and I–V response are supported by analysis of the charge distribution of the CP monolayer upon adsorption of CO, CO2, NH3, NO and NO2. Molecules have been calculated using density functional theory and non-equilibrium Green's function. The presented theoretical investigations reveal that the CP monolayer-based device exhibits improved characteristics and could be the foundation towards constructing highly sensitive nanosensor devices. [ABSTRACT FROM AUTHOR]

Two mononuclear complexes of Co(II) and Zn(II) with a [MO6] coordination sphere, [Co(L)2(H2O)2] (1) and [Zn(L)2(H2O)2] (2), are prepared and characterized through spectral, single crystal X-ray and DFT/TD-DFT studies. The X-ray structure reveals an octahedral geometry with all the oxygen donor sets around the metal ion. DFT studies confirm the cobalt complex is high spin with a +2 oxidation state. Time dependent density functional theory (TD-DFT) shows the electronic transitions to be metal to ligand (MLCT) and intra-ligand charge transfer (ILCT) type. The complexes consolidate the crystal lattice via extensive non-covalent interactions, which are verified by Hirshfeld surface analysis. These non-covalent interactions are also responsible for the enhanced DNA binding affinity of the complexes as confirmed theoretically by molecular docking studies. The Zn(II) complex binds to DNA with more affinity due to the lesser HOMO–LUMO energy gap calculated by DFT analysis. The complexes are assessed for catecholase like activity for oxidation of 3,5-DTBC to 3,5-DTBQ in ethanol. 1 shows catecholase activity with the parameters Kcat = 168.5 h−1, KM = 0.00043 M and Vmax = 4.68 × 10−2 M min−1. ESI-MS identifies possible intermediates formed during the catalytic cycle while EPR and cyclic voltammetry confirm the mechanism of the catalytic oxidation to be metal centered rather than radical formation. The catecholase activity of 1 and inactivity of 2 are also corroborated by density functional theory (DFT) analysis. The theoretical analysis results are in good agreement with the experimental findings concerning the structure, electronic spectra, DNA binding affinity and catecholase like activity. Most interestingly, the present Co(II) complex is discovered to be a better catecholase mimic and the activity could be tuned by modifications in the metal or structural features of the ligand(s) and complexes. [ABSTRACT FROM AUTHOR]

A new multifunctional NBD-based probe has been developed having high sensitivity and selectivity towards Cu2+/Ni2+ over other metal ions over a wide pH range. The probe 1 could be used for the simultaneous estimation of Cu2+ and Ni2+ ions through its visible color change from yellow to blue and light green, respectively, in semi-aqueous systems. The binding mode of probe 1 to Cu2+ and Ni2+ was determined to be a 1 : 1 complexation stoichiometry using a Job's plot. Ethylenediamine tetraacetate showed high selectivity towards the in situ prepared Cu2+ complex over the Ni2+ complex, which is applied to distinguish Ni2+ and Cu2+ ions. The detection limits for Cu2+ and Ni2+ ions, 1.8 × 10−7 M and 1.1 × 10−6 M, respectively, were lower than those recommended by the WHO guidelines for drinking water. Moreover, probe 1 could be used as a practical, visible colorimetric test kit for Cu2+ ions. The sensing mechanism of Cu2+ and Ni2+ ions was supported by DFT-calculations. [ABSTRACT FROM AUTHOR]

The role of the metal formal charge in the cation–π interactions has been evaluated with relativistic DFT methods involving a versatile π-cryptating structure, namely [2.2.2]paracyclophane. Our study focuses on experimentally characterized [([2.2.2]pCp)M]n+ systems with M = Ag+ and Sn2+ and their Cd2+ and In+ counterparts, which exhibit 5s05p0 and 5s25p0 electron configurations. The acceptor capabilities increase when the metal charges go from 1+ to 2+, resulting in a large stabilization of the interaction. For the studied 5s05p0 cations Ag+ and Cd2+, the most stable conformation namely [(η2:η2:η2-[2.2.2]pCp)M]n+, the electrostatic contribution is more favorable by −9.3 kcal mol−1, whereas the ΔEOrb contribution increases by −151.6 kcal mol−1 towards a more favourable situation in the 2+ counterpart. Similarly in the 5s25p0 cationic group, the isoelectronic Sn2+ and In+ systems depict variation of the electrostatic and orbital terms, with a considerable decrease of the stabilizing ΔEOrb contribution, and in a lesser amount the ΔEElstat term. Thus, the variation of the interaction energy between the M+ and M2+ isoelectronic counterparts can be ascribed mainly to the variation of the ΔEOrb term, leading to a more covalent character of the interaction retaining a similar bonding scheme. [ABSTRACT FROM AUTHOR]