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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]

In the process of handling and storage of radioactive actinides it is essential to selectively sequester the minor actinides, such as Am and Cm, through a competitive complexation process. Herein we computationally designed two core modified ligands (L21− and L3) through systematic oxygen substitution at the NH sites of dipyriamethyrin (L1_2H), a hexadentate expanded porphyrin, and studied their competitive complexation towards trivalent actinides (An = Am/Cm) from their trichlorides using density functional theory (DFT). We observed shorter An–N bonds and longer An–O bonds in complexes based on core modified ligands (L21− and L3). The An–Cl bond length increases with increasing axial coordination number (i.e., from L12− to L3) to accommodate the ligands. All the bonds were identified to be electrostatic in nature. L12− exhibits shorter bonds and larger bond orders on complexing with Am than with Cm. On moving from complexes of L21− to L3, the An–N bond lengths are shortened, while An–O bond lengths become larger. Between the complexes of Am and Cm, there is marginal difference in their bond distances with L21− and L3. Charge analysis shows ligand to metal charge transfer during coordination, with back-donation from An to N/O and Cl. The calculated spin-density analysis indicates that An remains in its trivalent oxidation state on complexation, while orbital occupation analysis shows that the 5f and 6d orbitals are involved in bonding; this was confirmed by molecular orbital (MO) analysis that shows the complexes of L21− and L3 to exhibit higher degeneracy in their overlapping MOs. Further, the energy decomposition analysis (EDA) confirms that all ionic bonds are primarily due to electrostatic contributions, where the orbital contributions increase from L12− to L3 complexes and maximum covalency was observed in Cm complexes due to the energy matching between the 5f orbitals of Cm and the 2p orbitals of N and Cl, compared to Am. To confirm the competitiveness in the complexation of the ligand towards Am vs. Cm, the thermodynamic parameters were analysed for the ligand and metal substitution reactions. L12− shows more affinity towards Am than Cm, while L21− and L3 prefer Cm. [ABSTRACT FROM AUTHOR]

A series of charge transfer cocrystals with fluorescence properties involving 1,2,4,5-tetracyanobenzene (TCNB, C10H2N4) as acceptor, fluorene (FR, C13H10) and its bromide 2-bromofluorene (2-BrFR, C13H9Br), carbazole (CZ, C12H9N) and its bromide 2-bromocarbazole (2-BrCZ, C12H8BrN) as donor were synthesized via cocrystal design strategies. The formation mechanism of the crystal structure was explored by density functional theory at the molecular level. The stacking structure of the cocrystal was formed by the combination of charge transfer interactions, π–π interactions and hydrogen bonding. The N atom of donors in TCNB–CZ and TCNB–2-BrCZ could enhance the charge transfer, appearing as a red shift of the fluorescence emission wavelength. Conversely, the Br atom in TCNB–2-BrFR and TCNB–2-BrCZ weakens the charge transfer, giving a blue shift in the fluorescence emission spectrum. The four new cocrystals exhibit tunable luminescence from green (529 nm) to yellow (552 nm) and to red (604 nm and 614 nm). It was found that the introduction of N and Br atoms in the assembly units can not only regulate the luminescence range of the cocrystals, but also adjust the luminescence efficiency, which provides a strategy for the development of promising organic luminescent materials. [ABSTRACT FROM AUTHOR]

Metalloviologens, as emerging electron-transfer photochromic compounds, have shown intriguing properties such as radiochromism, photochromism and photoconductance. However, only a limited number of them have been reported so far. Exploration of new metalloviologens is strongly desired. Herein, we report a new solvothermally synthesized metalloviologen complex [CdCl2(ND)2]n (1, ND = 1,5-naphthalenes) that exhibits photochromic and intrinsic white light emission properties. Density functional theory calculation results reveal that the photochromism could be assigned to photoinduced electron transfer from chlorine atoms to ND molecules. The photoinduced charge-separated states are heat/air stable, attributed to the delocalization of ND and strong intermolecular π–π interactions. Besides, complex 1 consistently emits intrinsic white light when excited with 340–370 nm UV light, achieving high color rendering index (CRI) values (82.54–94.04). By adjusting the excitation wavelength, both "warm" and "cold" white light emission can be produced, making it suitable for the application of a white light emitting diode (WLED). Thus, this work demonstrates that the ND-based metalloviologen is not only helpful in producing photochromism, but also beneficial for creating white-light emission. [ABSTRACT FROM AUTHOR]

In this paper, we synthesized layered crystals of bis(μ2-chlor)-tris(triphenylphosphine)-di-copper(I) (CTC) and bis(μ2-bromo)-tris(triphenylphosphine)-di-copper(I) (BTC) via electrochemical synthesis in an ambient environment. The crystal stands edge-on to the copper substrate in the electrochemical synthesis, which would enhance the charge transfer between the crystal and the substrate, promoting its photoelectric properties. Combined with density functional theory calculations, the optical absorption and emission are the crystals were studied to obtain a clarified mechanism. Using a chemical etching strategy, we can obtain BTC microtubes with tunable cavities, which can be used as microscopic containers. [ABSTRACT FROM AUTHOR]

Synthesis, characterization and thorough investigation of the photophysical and electrochemical properties of a new category of emissive homo- and heteroleptic Ru(II)-complexes derived from the [4′-(p-triphenylphosphonium methyl phenyl)-2,2′:6′,2′′-terpyridine]bromide (tpy-PhCH2PPh3Br) ligand have been executed in this work. Incorporation of the PhCH2PPh3+Br− group at the terpyridine motif appropriately adjusts the triplet metal-to-ligand charge transfer (3MLCT) and metal-centered (3MC) excited states so that the complexes luminesce at room temperature (RT) having lifetimes within the range of 6.82–9.63 ns. The RT emission characteristics of the complexes get further enhanced via aggregation phenomena through the use of different solvent/non-solvent mixtures (DMSO/H2O and DMSO/PhCH3 mixtures). Temperature dependent emission spectral measurements indicate that the emission intensity, quantum yield and lifetime increase upon dropping down the temperature, thereby designated as the on-state, while the increase of temperature causes a reduction of the said properties, indicating the off-state and the process is fully reversible. Taking advantage of the active methylene group coupled with a phosphonium motif, anion sensing characteristics of the complexes are investigated systematically in DMSO through the use of various optical channels and spectroscopic tools. The complexes are very much sensitive to fluoride and to a lesser extent acetate and dihydrogen phosphate among the studied anions. In essence, the complexes function as sensors for temperature and fluoride ion. Computational investigations were also executed via density functional theory (DFT) and time-dependent (TD)-DFT to obtain a clear understanding of the electronic structures of the metalloreceptors, appropriate assignment of the spectral bands and their mode of interaction with selected anions. [ABSTRACT FROM AUTHOR]

Nitrogen complexation with π-conjugated ligands is an effective strategy for synthesizing luminescent molecules. The asymmetric bridging ligands L (L1 and L2) have been designed. The terminal chelating sites of the L1 and L2 bridging ligands consisted of 2,2′-bipyridine (bpy) and 1,10-phenanthroline moieties (where L = L1 and L2; L1 = 2-(3-((4-([2,2′-bipyridin]-6-yl)benzyl)oxy)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline and L2 = 2-(3-((4-(6-phenyl-[2,2′-bipyridin]-4-yl)benzyl)oxy)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline). The full use of the synthetic strategy of the “complexes as ligands and complexes as metals” was expected to successfully design and synthesize a series of conjugated metal-exchange complexes linked by the asymmetric bridging ligands L1 and L2. These compounds included monometallic complexes Ru(L) and (L)Ru (C1, C2, C7, and C8), homometallic complexes Ru(L)Ru (C3 and C4), and heterometallic complexes Os(L)Ru and Ru(L)Os (C5, C6, C9, and C10) with Ru- or Os-based units. C3–C10 complexes exhibited various degrees of octahedral distortion around the Ru(II) or Os(II) center, which was consistent with the optimized geometry of the coordination complexes based on density functional theory calculation. These complexes exhibited intense spin-allowed ligand-centered transitions with high absorbance at around 288 nm upon absorbing visible light. Notably, all complexes exhibited spin-allowed metal-to-ligand charge transfer absorption of the Ru-based units in the 440–450 nm range. In addition, the heterometallic C5, C6, C9, and C10 complexes showed absorption of the Os-based units in the range of 565–583 nm. The intramolecular energy transfer of C3 and C5 was briefly discussed by comparing the emission intensity of monometallic C1 and C2 to that of binuclear complexes C3 and C5, respectively. The results indicated that the intramolecular energy transfer of the Ru(II)/Os(II) polypyridine complexes proceeded from the Ru(II)- to the Os(II)-based units in the heterometallic C5 and C6 complexes. [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]

Platinum(II) complexes with salophen ligands bearing carboxy substituents at different positions, [Pt{(COOH)n–salophen}] (n = 2 (1), 3 (2), 1 (3)), were synthesized and characterized by acquiring UV-vis and luminescence spectra. These complexes exhibited systematic variations in absorption spectra depending on the number of carboxy groups, and this effect was attributed to metal–ligand charge transfer with support from density functional theory calculations. The luminescence properties of these complexes were also correlated with structural differences. Complexes 1–3 showed systematic spectral changes by addition of organic acid and base, respectively. This is based on the protonation/deprotonation of the carboxy substituents. Furthermore, aggregation-induced spectra change was investigated in DMSO–H2O mixtures with various proportions of water. Peak shifts in the range of 95 to 105 nm occurred in the absorption spectra in conjunction with pH changes. These variations resulted from molecular aggregation and diffusion associated with protonation/deprotonation of the carboxy groups. Variations in luminescence emission intensity and peak shifts were also observed. This work provides new insights into the correlations between the optical properties of carboxy-appended molecular complexes and pH changes and will assist in the future design of pH sensing devices based on molecular metal complexes. [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]

A cationic Ir(III) complex, Ir2, with a diphenylamino (DPA)-substituted 2-phenylbenzothiazole derivative as the cyclometalating ligand was designed and synthesized. Ir2 shows obvious aggregation-induced phosphorescent emission (AIPE) in H2O/CH3CN, compared with a non-DPA-substituted Ir1. The AIPE-active Ir2 demonstrates efficient detection of 2,4,6-trinitrophenol, providing a higher quenching constant (KSV = 2 644 330 M−1vs. 73 583 M−1 for Ir1) and a lower limit of detection (LOD = 2.23 nM vs. 50.17 nM for Ir1). High-resolution mass spectrometry analysis and density functional theory calculations demonstrate that photoinduced electron transfer may be responsible for the emission quenching. Immobilized in an ethyl cellulose film, Ir2 exhibits high oxygen sensitivity (K appSV = 0.0572 Torr−1vs. 0.0090 Torr−1 for Ir1) and excellent reversibility in 10 cycles. This work reveals that the DPA group plays an important role in tuning the AIPE properties and increasing the performances of the luminescent probes. [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]

Unusual intermolecular π-stacking in a new charge transfer salt of pyrene (Py), (Py)2+(Ga2Cl7)−, has been observed. The structure obtained by single crystal X-ray crystallography indicates π-stacks of pyrene which were analyzed using a combination of density functional theory and the analysis of the bond length alternation patterns in the pyrene molecules in different charge states. There are relatively few crystal structures of charge transfer salts of pyrene in the literature, and this structure shows a unique charge separation in which half of the pyrenes are nearly neutral while the other half carry approximately +1 charge in an alternating fashion along the 1D stacks balancing one electron charge transfer to each (Ga2Cl7)− anion. The charge localization is attributed to the incomplete inter-pyrene overlap of the singly occupied molecular orbitals. [ABSTRACT FROM AUTHOR]

Complex formation between uranyl and carboxylate ligands (benzoate, nicotinate and isonicotinate) has been studied extensively by absorption and luminescence spectroscopy in acetonitrile medium. Experimental data had indicated the existence of stable and enhanced luminescent tris(carboxylato) uranyl(VI) complexes i.e. [UO2(L)3]− with D3h symmetry. The high luminescence of these complexes was due to the sensitization of the Oyl → U ligand to metal charge transfer (LMCT) emission by extremely intense equatorial (carboxylate ligands) LMCT bands. The variation in the experimentally observed parameters such as intensity of equatorial LMCT bands, luminescence lifetimes, quantum yields and structural parameters among tris(carboxylato) uranyl(VI) complexes are affirmed by quantum chemical calculations using density functional theory and the computational results are found to be in good agreement with experimental findings. Interestingly, in a very dilute mixture of [UO2(L)3]− and Eu(III), energy transfer from uranyl to Eu(III) is observed and it leads to the detection of europium at trace levels. This is an intriguing observation as none of the previous studies have reported such a low level of detection limit of Eu(III) by means of energy transfer from any metal. [ABSTRACT FROM AUTHOR]

Charge transfer cocrystals offer an opportunity to construct high performance organic photothermal materials. However, it is still challenging to modulate the degree of charge transfer of cocrystals to achieve rationally designed photothermal functional materials. Herein three charge transfer cocrystals composed of carbazole (CZ)/3,6-dichlorocarbazole (ClCZ)/3,6-dibromocarbazole (BrCZ) as π-donors (D) and 7,7′,8,8′-tetracyanoquinodimethane (TCNQ) as a π-acceptor (A), namely CZ/TCNQ, ClCZ/TCNQ and BrCZ/TCNQ, were obtained and subjected to spectroscopic and photothermal conversion studies as well as density functional theory calculations. The crystal structures reveal that the donor and acceptor molecules of each cocrystal adopt a ⋯DADADA⋯ mixed stack structure. With steric hindrance and electron withdrawing effects of chlorine/bromine atoms on carbazole, the charge transfer degree of CZ/TCNQ is reduced from 0.25 to 0.07 for ClCZ/TCNQ and 0.03 for BrCZ/TCNQ. The three cocrystals display broad absorption over the 300 to 900 nm range without significant photon emission. The near-infrared photothermal conversion efficiency reaches 53.7% (CZ/TCNQ), 48.5% (ClCZ/TCNQ) and 32.0% (BrCZ/TCNQ), respectively. These cocrystals have narrowed HOMO–LUMO gaps, which is attributed to the strong charge transfer transition and agrees with the photophysical and photothermal conversion properties of the cocrystals. This study demonstrates that the modulation of the charge transfer degree by intelligent design of donor–acceptor pairs can be an effective means to regulate the photothermal conversion efficiency of charge transfer cocrystals. Finally, CZ/TCNQ was successfully applied as an appealing photothermal material in photothermal imaging and functional electrical device control. [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]

Synthesis and isolation of molecular building blocks of metal–organic frameworks (MOFs) can provide unique opportunities for characterization that would otherwise be inaccessible due to the heterogeneous nature of MOFs. Herein, we report a series of trinuclear cobalt complexes incorporating dithiolene ligands, triphenylene-2,3,6,7,10,11-hexathiolate (THT) (13+), and benzene hexathiolate (BHT) (23+), with 1,1,1,-tris(diphenylphosphinomethyl)ethane (triphos) employed as the capping ligand. Single crystal X-ray analyses of 13+ and 23+ display three five-coordinate cobalt centers bound to the triphos and dithiolene ligands in a distorted square pyramidal geometry. Cyclic voltammetry studies of 13+ and 23+ reveal three redox features associated with the formation of mixed valence states due to the sequential reduction of the redox-active metal centers (CoIII/II). Using this electrochemical data, the comproportionality values were determined for 1 and 2 (log Kc = 1.4 and 1.5 for 1, and 4.7 and 5.8 for 2), suggesting strong resonance-stabilized coupling of the metal centers, with stronger electronic coupling observed for complex 2 compared to that for complex 1. Cyclic voltammetry studies were also performed in solvents of varying polarity, whereupon the difference in the standard potentials (ΔE1/2) for 1 and 2 was found to shift as a function of the polarity of the solvent, indicating a negative correlation between the dielectric constant of the electrochemical medium and the stability of the mixed valence species. Spectroelectrochemical studies of in situ generated multi-valent (MV) states of complexes 1 and 2 display characteristic NIR intervalence charge transfer (IVCT) bands, and analysis of the IVCT transitions for complex 2 suggests a weakly coupled class II multi-valent species and relatively large electronic coupling factors (1700 cm−1 for the first multi-valent state of 22+, and 1400 and 4000 cm−1 for the second multi-valent state of 2+). Density functional theory (DFT) calculations indicate a significant deviation in relative energies of the frontier orbitals of complexes 13+, 23+, and 3+ that contrasts those calculated for the analogous trinuclear cobalt dithiolene complexes employing pentamethylcyclopentadienyl (Cp*) as the capping ligand (Co3Cp*3THT and Co3Cp*3BHT, respectively), and may be a result of the cationic nature of complexes 13+, 23+, and 3+. [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]

Sluggish charge transfer is the major problem which restricts the development of metal–organic framework (MOF)-based photocatalysts. Recently, facet-engineering has been proven to be an effective method for solving this issue. However, due to difficulties in regulating the exposed facets of MOFs, there are few reports about the facet-engineering of MOF-based photocatalysts. Here, we firstly report facet-engineering for promoting the photocatalytic activity of NH2-UiO-66 crystals. In this study, by regulating the influence of kinetics and thermodynamics, cubic, tetra-decahedral, and octahedral forms of NH2-UiO-66 are synthesized. The photocatalytic hydrogen evolution rate of tetra-decahedral NH2-UiO-66 with co-exposed (100) and (111) crystal facets reaches 64.06 μmol g−1 h−1, which is approximately 2 and 1.5 times greater than that of the cubic and octahedral forms of NH2-UiO-66, respectively. The density functional theory (DFT) calculation and ultrafast spectroscopy results indicate that a slight staggering exists in the band structure of (100) and (111) facets, causing the facets junction to appear. The facet junction promotes the charge separation efficiency and prolongs the lifetime of the charge carriers, thereby giving tetra-decahedral NH2-UiO-66 optimal photocatalytic performance. This study demonstrates the feasibility and potential of facet-engineering for photocatalytic applications of MOFs. [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]

Molecular engineering schemes are essential for the construction of highly efficient and tunable long-wavelength fluorescent materials from the perspective of crystal engineering. Herein, three charge transfer (CT) cocrystals (Ia, Ib, and Ic) are successfully fabricated using cyanostilbene (CS) derivatives with various polycyclic motifs (naphthalene, anthracene, or pyrene) as the donor compounds and 1,2,4,5-tetracyanobenzene (TCNB) as the acceptor unit to tune their photophysical characteristics. The three CT cocrystals exhibit mixed stack arrangements in which the donor and acceptor align in a face-to-face fashion (Ia: DADA, Ib, and Ic: DAD–DAD) as revealed by single-crystal X-ray diffraction (SCXRD). These organic hybrid materials display tunable multicolor luminescence from yellow (Ia: 554 nm) to red (Ib: 650 and Ic: 620 nm) in the solid state depending on the polycyclic motif ionization potential (IP) as well as the organization of the donor species in the framework. Furthermore, the results of density functional theory (DFT) calculations also support the observed red-shifted emission of the three products. These results demonstrate that the engineering of CS is an effective approach for the development of future two-component multicolor fluorescent complexes, which could find applications in optoelectronic and electronic devices. [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]

The synthetic approaches for the preparation of trans(NO,OH)-cis(NO2,NO2)-[RuNO(L)2(NO2)2OH], where L = ethyl nicotinate (I) and methyl nicotinate (II), are reported. The structures of the complexes are characterized by X-ray diffraction and analyzed by Hirshfeld surface analysis. Both compounds show a nitric oxide release reaction under 445 or 532 nm irradiation of dimethyl sulfoxide (DMSO) solutions, which is studied by combined ultraviolet-visible- (UV-vis), infrared- (IR), and electron paramagnetic resonance (EPR) spectroscopy and density functional theory (DFT) calculations. The charge transfer from the OH–Ru–NO chain and nitrite ligands to the antibonding orbitals of Ru–NO is responsible for the photo-cleavage of the ruthenium–nitrosyl bond. The elimination of NO leads to a side reaction, namely the protonation of the parent hydroxyl compound. The cytotoxicity and photo-induced cytotoxicity investigations of both compounds on the breast adenocarcinoma cell line MCF-7 reveal that (I) and (II) are cytotoxic with IC50 values of 27.5 ± 2.8 μM and 23.3 ± 0.3 μM, respectively. Moreover, (I) shows an increase of the toxicity after light irradiation by 7 times (IC50 = 4.1 ± 0.1), which makes it a prominent target for deeper biological investigations. [ABSTRACT FROM AUTHOR]

Elucidating the structure–property relationships of ultra-small metal nanocluster with basic nuclear is of great significance for understanding the evolution mechanism in both the structures and properties of polynuclear metal nanoclusters. In this study, an ultra-small copper hydride (CuH for short) nanocluster was simply synthesized with high yield, and the large-scale preparation was also achieved. Single crystal X-ray diffractometer (SC-XRD) analysis shows that this copper NC contains a tetrahedral Cu4 core co-capped by four PPh2Py ligands and two Cl in which the existence of the central H atom in tetrahedron was further identified experimentally and theoretically. This CuH nanocluster exhibits bright yellow emission, which is proved to be the mixture of phosphorescence and fluorescence by the sensitivity of both emission intensity and lifetime to O2. Furthermore, the temperature-dependent emission spectra and density functional theory (DFT) calculations suggest that the luminescence of CuH mainly originates from the metal-to-ligand charge transfer and cluster-centered triplet excited states. This work offers new insights into understanding the structure–property relationship of basic nuclear CuH nanocluster. [ABSTRACT FROM AUTHOR]

The reaction of a triazole ligand, 2-(1H-1,2,3-triazol-4-yl)pyridine (L1), with 2-bromopyridine afforded three new ligands, 2,2′-(1H-1,2,3-triazole-1,4-diyl)dipyridine (L2), 2,2′-(2H-1,2,3-triazole-2,4-diyl)dipyridine (L3) and 2,2′-(1H-1,2,3-triazole-1,5-diyl)dipyridine (L4). A series of luminescent mononuclear copper(I) complexes of these ligands [Cu(Ln)(P^P)](ClO4) [n = 1, P^P = (PPh3)2 (1); n = 1, P^P = POP (2); n = 2, P^P = (PPh3)2 (3); n = 2, P^P = POP (4); n = 3, P^P = (PPh3)2 (5); n = 3, P^P = POP (6); n = 4, P^P = (PPh3)2 (9); n = 4, P^P = POP (10)] have been obtained from the reaction of Ln with [Cu(MeCN)4]ClO4 in the presence of PPh3 and POP. L3 was also found to form dinuclear compounds [Cu2(L3)(PPh3)4](ClO4)2 (7) and [Cu2(L3)(POP)2](ClO4)2 (8). All of the Cu(I) compounds have been characterized by IR, UV/vis, CV, 1H NMR, and 31P{1H} NMR. The molecular structures of 1–3, 5, and 7 have been further determined by X-ray crystallography. In CH2Cl2 solutions, these Cu(I) complexes exhibit tunable green to orange emissions (563–621 nm) upon excitation at λex = 380 nm. In the solid state, these complexes show intense emissions and it is interesting to note that 1 and 3 are blue-light emitters. Density functional theory (DFT) calculations revealed that the lowest energy electronic transition associated with these complexes predominantly originates from metal-to-ligand charge transfer transitions (MLCT). [ABSTRACT FROM AUTHOR]

A novel Ru(II) complex with a donor–acceptor–donor (D–A–D) ligand was designed and synthesized to prepare organic memory devices. The fabricated Ru(II) complex-based devices exhibited obvious bipolar resistance switching behavior with a low switching voltage (∼1.13 V) and a large ON/OFF ratio (105). The dominant switching mechanism can be explained by the distinct charge-transfer states endowed by the interaction between metals and ligands, which is verified by density functional theory (DFT) calculations. Excitingly, the device displays a much lower switching voltage than most of the previously reported metal complex based memory devices due to the intense intramolecular charge transfer caused by the strong built-in electric field in D–A systems. This work not only reveals the potential of the Ru(II) complex in resistive switching devices, but also provides new inspiration to manipulate the switching voltage at the molecular level. [ABSTRACT FROM AUTHOR]

The construction of an efficient non-noble-metal electrocatalyst towards alkaline hydrogen evolution is challenging but in great demand. The fabrication of a porous nanostructure and heteroatom doping are two productive strategies for developing effective electrocatalysts. In this contribution, we report the preparation of La, Ce and Er-doped Ni2P porous nanostructures through a facile water bath method and phosphorization strategy. The Er-doped Ni2P porous nanostructure exhibits superb hydrogen evolution reaction (HER) catalytic performance under alkaline conditions with a low cathodic overpotential of 87 mV (10 mA cm−2, glassy carbon) and a small Tafel slope of 65.4 mV dec−1. It also displays excellent electrochemical stability in alkaline electrolytes. First-principles density functional theory (DFT) calculations disclosed the mechanism of the alkaline HER catalysis. For pristine Ni2P, the P site acts as the optimal active site with the Gibbs free energy of H* absorption (ΔGH*) of 0.48 eV. After La, Ce and Er are doped, respectively, the P site is still the active center of the three doping systems. Notably, the ΔGH* value is reduced from 0.48 eV to 0.23 eV (P site in La-doped Ni2P), 0.20 eV (P site in Ce-doped Ni2P) and 0.18 eV (P site in Er-doped Ni2P), suggesting that doping with La, Ce and Er atoms plays a crucial role in decreasing the H* absorption energy on optimal P sites and the optimum active site with a smaller ΔGH* can expedite the charge transfer rate for H* midbody and H2 generation. This is particularly noticeable for Er doping, which is in accordance with the experimental result. [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]