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Here, we introduce a hybrid method, named Kick-Fukui, to explore the potential energy surface (PES) of clusters and molecules using the Coulombic integral between the Fukui functions in the first screening of the best individuals. In the process, small stable molecules or clusters whose combination has the stoichiometry of the explored species are used as assembly units. First, a small set of candidates has been selected from a large and stochastically generated (Kick) population according to the maximum value of the Coulombic integral between the Fukui functions of both fragments. Subsequently, these few candidates are optimized using a gradient method and density functional theory (DFT) calculations. The performance of the program has been evaluated to explore the PES of various systems, including atomic and molecular clusters. In most cases studied, the global minimum (GM) has been identified with a low computational cost. The strategy does not allow to identify the GM of some silicon clusters; however, it predicts local minima very close in energy to the GM that could be used as the initial population of evolutionary algorithms.

It is here reported that the NaBH3- cluster exhibits a Na⋅B one-electron bond, a well-established type of electron-deficient bonding in the literature. The topological analysis of the electron localization function, at the correlated level, reveals that Na- , when approaching the bonding distance, fairly distributes its valence electron pair between two lobes. One of these electrons is used to bond with BH3 , which participates through its boron empty p-orbital. Furthermore, the bonding situation of LiBH3- , KBH3- , MgBH3 , and CaBH3 global minima structures are similar to that of NaBH3- , extending the family of these new one-electron bond systems with biradicaloid character.

Expanded porphyrins arise as an alternative for potential application as chromophores in dye-sensitized solar cells. (DSSCs). The modification of the core of these compounds provides remarkable changes in the photoelectronic behavior. In the present article, the improvement of its properties for a potential application as UV/vis/NIR chromophores in DSSCs has been studied, when an oxazolone moiety has replaced an imine ring in analogy to the porpholactones first synthesized by Crossley et al. ( J. Chem. Soc., Chem. Commun. 1984, 920-922). These expanded porpholactones present a noticeable red shift as well as an increase in the intensity of the Q-bands regarding the parent compounds. The photophysical properties of Sapphyrin have been explored through DFT calculations and vibrationally resolved absorption spectra simulations. Energetic parameters showed favorable electron injection from the chromophore to the TiO2 semiconductor. In addition, aromaticity was analyzed and rationalized using magnetic and delocalization criteria. Results showed qualitatively similar trends between aromaticity descriptors and Q bands giving a great opportunity to the use this property in the rational design of chromophores. Finally, the nonequilibrium Green's function formalism shows the ability of expanded porpholactones in electron transport.

Here, we analyze the possibility of predicting local and global current densities in a series of bicyclic hydrocarbons with 4n and 4n + 2 π-electrons from the nucleus-independent chemical shifts (NICS) computations. Our results show that although it is possible to establish the net current flows through C–C bonds, it is impossible to predict all the local and global weak current density flows. Thus, for polycyclic systems, it is essential to analyze magnetically induced current densities in conjunction with NICS measurements, or with induced magnetic fields, to have an adequate representation of the molecules’ magnetic behavior and their relationship with the aromaticity phenomenon.

Despite the belief that noble gases (Ng) are completely inert and cannot form stable molecules, a variety of Ng compounds have been reported under laboratory conditions and others were recently detected in the interstellar media, raising interest in knowing and studying their bond nature and the physicochemical properties associated with their stability. In the present work, a systematic analysis of the thermodynamic stability of noble gas halide cations (NgX+ ) at the CCSD(T)/def2-QZVP level have been performed. In addition, chemical bond was characterized through Natural Bonding Theory (NBO), Quantum Theory of Atoms in Molecules (QTAIM) and Energy Decomposition Analysis (EDA) with relativistic corrections. All methods suggest that NgX+ compounds possess a strong covalent bond. However, results show that only compounds containing Ar-Rn atoms are thermodynamic stable with a highly energetic and endergonic dissociation process. For these reasons, it is possible to suggest that several compounds that have not yet been reported could be obtained at the laboratory level or observed in the interstellar medium.

The relativistic effects on the aromaticity of a set of benzene analogues, E3M3H3 (E = C–Pb; M = N–Bi) heterocycles, using magnetically induced current density (MICD) and the NICSzz component of the conventional nucleus independent chemical shift (NICS), is hereby examined. The relativistic effects were evaluated by means of four-component relativistic MICD, and two-component NMR relativistic shielding tensor methods. MICD and NICS were also computed in a non-relativistic fashion, to assess the influence of scalar-relativistic and spin–orbit effects. Most of the studied compounds exhibit a net diatropic ring current (aromatic), excluding the nitrogen-containing compounds which are non-aromatic (except for C3N3H3), in agreement with their higher E–N electronegativity difference. Only in the case of bismuth compounds, E3Bi3H3, aromaticity is substantially decreased when relativistic effects are included (mainly due to the spin–orbit contribution). The larger the mass of the system, the larger the magnitude of this change, in line with the expected relativistic effects for heavier elements. The analysis based on the NICSzz computations agrees with that of the MICD, thus supporting both the magnetic behavior and the aromatic character of these compounds.

We computationally explore an alternative to stabilize one-dimensional (1D) silicon-lithium nanowires (NWs). The Li12Si9 Zintl phase exhibits the NW [Li6Si5]∞1, combined with Y-shaped Si4 structures. Interestingly, this NW could be assembled from the stacking of the Li6Si5 aromatic cluster. The [Li6Si5]∞1@CNT nanocomposite has been investigated with density functional theory (DFT), including molecular dynamics simulations and electronic structure calculations. We found that van der Waals interaction between Li’s and CNT’s walls is relevant for stabilizing this hybrid nanocomposite. This work suggests that nanostructured confinement (within CNTs) may be an alternative to stabilize this free NW, cleaning its properties regarding Li12Si9 solid phase, i.e., metallic character, concerning the perturbation provided by their environment in the Li12Si7 compound.

International audience; Transparent and colorless solar cells are attractive new photovoltaic devices as they could bring new opportunities to harness sunlight energy and particularly for their integrations in windows. In this work, a new zinc phthalocyanine was synthesized and investigated as sensitizer in dye sensitized solar cell (DSSC) for this purpose. The zinc phthalocyanine features a benzoic acid anchoring group and six thio(4-tertbutylphenyl) substituents in position alpha of the phtalocyanine. The dye was characterized by absorption and emission spectroscopy and by electrochemistry. The physico-chemical properties show that the dye fulfills the criteria for such an application. A detailed computational study indicates that the electronic communication with TiO2 conduction is weak owing to the absence of overlapping of the wavefunctions of the dye with those of the TiO2 semiconductor. The photovoltaic performances of the zinc phthalocyanine were measured in TiO2 based DSSC and revealed inefficient electron injection and certainly explained by the weak electronic coupling of the 2 dye with TiO2 that limits electron injection efficiency. Strategy is proposed to make better performing sensitizers.; Les cellules solaires transparentes et incolores sont de nouveaux dispositifs photovoltaïques attrayants car ils pourraient offrir de nouvelles possibilités d'exploiter l'énergie du soleil, notamment pour leur intégration dans les fenêtres. Dans ce travail, une nouvelle phtalocyanine de zinc a été synthétisée et étudiée comme sensibilisateur dans une cellule solaire sensibilisée par un colorant (DSSC). La phtalocyanine de zinc présente un groupe d'ancrage acide benzoïque et six substituants thio(4-tertbutylphényle) en position alpha de la phtalocyanine. Le colorant a été caractérisé par spectroscopie d'absorption et d'émission et par électrochimie. Les propriétés physico-chimiques montrent que le colorant remplit les critères pour une telle application. Une étude computationnelle détaillée indique que la communication électronique avec la conduction du TiO2 est faible en raison de l'absence de recouvrement des fonctions d'onde du colorant avec celles du semi-conducteur TiO2. Les performances photovoltaïques de la phtalocyanine de zinc ont été mesurées dans des DSSC à base de TiO2 et ont révélé une injection d'électrons inefficace, certainement expliquée par le faible couplage électronique du colorant avec le TiO2 qui limite l'efficacité de l'injection d'électrons. Une stratégie est proposée pour fabriquer des sensibilisateurs plus performants.

The larger stability of phenacenes compared to their acene isomers in their ground states is attributed to the larger aromaticity of the former. To our knowledge the relative stability of acenes and phenacenes in their lowest-lying triplet states (T1) has not been discussed yet. Using unrestricted density functional theory calculations, our results show that for the smallests members of the series, acenes in their T1 states are more stable than the corresponding phenacenes. However, when the number of the rings (n) involved increases, the energy difference is reduced and for n > 12, phenacenes become more stable than acenes in their T1 states. To rationalize this trend, we analyze the aromaticity of acenes and phenacenes using a set of aromaticity descriptors. We find that in the T1 states of both acenes and phenacenes, the outer rings form aromatic Clar π-sextets. In acenes, delocalization of spin density in the central rings leads to the preferred formation of the largest antiaromatic diradical. Resonant structures in the form of antiaromatic diradical Baird π-octadectets and π-tetradectets are the major contributors, while the smaller ones, such as π-doublets and π-sextets, contribute the least. In phenacenes, structures with diradical antiaromatic Baird π-sextets in some of the central rings contribute the most. These results are relevant to understand the (anti)aromaticity of larger polycyclic aromatic hydrocarbons in their triplet states R.B-G. is grateful for the financial support of FONDECYT Postdoctorado 3210037. Powered@NLHPC. This research was partially supported by the supercomputing infrastructure of the NLHPC (ECM-02). M.S. acknowledges the financial support from the Ministerio de Economía y Competitividad of Spain (project CTQ2017-85341-P) and the Generalitat de Catalunya (project 2017SGR39)

An alternative response function, based on the dual descriptor in terms of Koopmans' approximation, is hereby proposed for the description of chemical reactivity in systems with (quasi-) degenerate frontier molecular orbitals. This descriptor is constructed from Fukui functions that include contributions from different orbitals, i.e., orbital-weighted Fukui functions. The methodology is applied to three case studies: the first case consists of a series of benchmark organic and inorganic molecules from which the dual descriptor, based only on frontier orbitals, is not appropriate to describe their reactivity. The second case deals with the proper description of chemical reactivity in Diels-Alder reactions between fullerene C60 and cyclopentadiene (CP), revealing the importance of considering secondary orbital interactions for an adequate regioselectivity description. The third, and last case, consists of a series of polycyclic aromatic hydrocarbons (PAHs) possessing molecular orbital degeneracy. By means of analyzing of this descriptor, an alternative approach to the description of aromaticity is proposed. In all cases, the proposed index called "orbital-weighted dual descriptor" has proven to accurately describe the chemical reactivity and aromaticity of the studied systems.

In all molecules, a current density is induced when the molecule is subjected to an external magnetic field. In turn, this current density creates a particular magnetic field. In this work, the bifurcation value of the induced magnetic field is analyzed in a representative set of aromatic, non‐aromatic and antiaromatic monocycles, as well as a set of polycyclic hydrocarbons. The results show that the bifurcation value of the ring‐shaped domain adequately classifies the studied molecules according to their aromatic character. For aromatic and nonaromatic molecules, it is possible to analyze two ring‐shaped domains, one diatropic (inside the molecular ring) and one paratropic (outside the molecular ring). Meanwhile, for antiaromatic rings, only a diatropic ring‐shaped domain (outside the molecular ring) is possible to analyze, since the paratropic domain (inside the molecular ring) is irreducible with the maximum value (attractor) at the center of the molecular ring. In some of the studied cases, i. e., in heteroatomic species, bifurcation values do not follow aromaticity trends and present some inconsistencies in comparison to ring currents strengths, showing that this approximation provides only a qualitative estimation about (anti)aromaticity.

A systematic study for the rational design of porphyrins (P4 spider-shaped derivatives) with potential application in dye-sensitized solar cells is presented. Using density functional theory (DFT) (B3LYP/6-31G*) and time-dependent DFT (M06/6-31G*) we show that the UV-vis absorption properties of a spider-shaped Zn(ii) porphyrin, previously synthesized by Stangel et al., may be greatly improved by applying some push-pull strategies in meso positions. We found that the selected triphenylamine push group induces a remarkable improvement in the absorption bands of P4 spider-shaped derivatives. The pull effect reached through the π-electron-rich phenyl group and the benzodithiazole (BTD) group allowed the Q bands to be red-shifted up to 689 nm, much longer than the 593 nm reported experimentally for the original spider-shaped porphyrin. The adsorption results of the P4 spider-shaped derivatives onto a TiO2-anatase surface model [Ti16O34H4] through the carboxylic acid group showed that the adsorptions energies were favourable and very similar in all cases. Natural bond orbitals (NBO) indicated a two-center bond (BD) O(carboxyl)-Ti(TiO2) for the porphyrin with the highest adsorption energy (8.27 kcal mol-1), and donor acceptor interactions from LP O(carboxyl) to Ti(TiO2) for the other porphyrins. The natural transition orbitals (NTO) for P4-derivatives-TiO2 confirm the nature of the excited states associated with Q and Soret bands. Finally, the frontier molecular orbitals revealed charge-separated states between those occupied and unoccupied, indicating a favourable charge-transfer process between the dyes and the surface conduction bands. In conclusion, this work showed a systematic study based on the push-pull strategy that improves the performance of porphyrins with the purpose to be used in dye-sensitized solar cells.

The capability of the BH2+ parent cation to bind noble gases (Ng) has been evaluated. The results show its potential to form borenium (BH2Ng+) and boronium (BH2Ng2+) cations. Conformational search using the recently developed AUTOMATON program and Coalescence Kick method, in addition to thermochemical and Born–Oppenheimer molecular dynamics (BOMD) calculations, were performed. Results show that compounds containing Ng = Ar–Rn are thermodynamically and kinetically stable. Furthermore, it was found that the B–Ng bond has high dissociation energy values at both DFT and CCSD(T) levels suggesting a strong interaction. The nature of the chemical bond has been assessed according to the Quantum Theory of Atoms in Molecules (QTAIM), Natural Bond Orbital Theory (NBO) and Energy decomposition Analysis (EDA). Negative values of local energy density H(rc) and high values of the Wiberg bond Index (WBI) reveal its covalent nature that is confirmed by localized natural bond orbitals with 2.0 |e| occupations. Additionally, it could be observed that the orbital term (ΔEorb) is the most important component (84.6–90.1%) of the interaction energy between the parent BH2+ and Ng atoms, supporting the polar covalent nature of the B–Ng bond.

Indole (1) is a heterocyclic aromatic compound consisting of a pyrrole ring (5MR) fused with a benzene ring (6MR). This compound is highly stable, found in several natural products, and used as a building block for the synthesis of novel organic compounds. On the other hand, its isomers isoindole (2) and indolizine (3) are much less stable and are normally isolated when bonded to other stable compounds. The stability of these compounds has been analyzed in terms of local aromaticity using magnetic, geometric, and delocalization criteria. All criteria used indicate that there is a continuing reduction in aromaticity of the 6MR whereas, for the 5MR, the aromaticity increases when going from 1 to 3. This is confirmed by Natural Resonance theory calculations indicating that the resonant structures which retain the aromaticity of 5MR are the ones having the largest contribution. The results obtained suggest that the relative stability of indole isomers is a consequence of the Glidewell-Lloyd rule M.S. acknowledges the financial support from the Ministerio de Economía y Competitividad of Spain (project CTQ2017-85341-P) and the Generalitat de Catalunya (project 2017SGR39)

The aromaticity in porphyrinoids results from the π conjugation through two different annular perimeters: the macrocyclic ring and the local heterocyclic rings appended to it. Analyses, based on aromatic stabilization energies (ASE), indicate that the local circuits (6π) are responsible for the significant aromatic stabilization of these systems. This local aromaticity can be coupled with the one from 4n + 2π macrocyclic circuit. It can either compensate for the destabilization due to a 4n π macrocyclic circuit, or be the only source of aromatic stabilization in porphyrinoids with macrocycles without π-conjugated bonds. This “multifaceted” aromatic character of porphyrinoids makes it challenging to analyze their aromaticity using magnetic descriptors because of the intricate interaction of local versus macro-cyclic circulation. In this contribution, we show that the analysis of the bifurcation of the induced magnetic field, Bind, allows clear identification and quantification of both local, and macrocyclic aromaticity, in a representative group of porphyrinioids. In porphyrin, bifurcation values accurately predict the local and macrocyclic contribution rate to overall aromatic stabilization determined by ASE.

Herein the performance of a modification within the hybrid algorithm implemented in the AUTOMATON program is introduced and evaluated. For the creation of the initial population, AUTOMATON combines a probabilistic automata procedure with a genetic algorithm used to evolve this population. The proposed modification is addressed to efficiently identify the minimum energy structures of systems composed of more than one type of atom and with a low computational cost. The effectiveness of this approach is evaluated in the determination of the minimum energy structures of Be6B11−. The modification, aimed to explore the potential energy surface, consisted of filling the cells first with Be atoms in the process of creating the initial population. This order obeys the structural pattern established in the Be–B clusters reported to date. The results show that this variation not only identifies a more significant number of viable isomers but also to find a better putative global minimum than those previously reported in the literature. Therefore, it is recommended to be used as a complement to the standard searching process.

Indexación: Scopus. The aromaticity of benzene, Al4 2- cluster, cyclopropane, borazine and planar cyclooctatetraene (COT) was analyzed according to different strategies based on nucleus-independent chemical shift (NICS) computations. The analysis of NICS-components evolution along the main molecular axis seems to be the most adequate and simplest strategy to predict the aromatic or antiaromatic character of the studied systems. Moreover, the analysis of the σ- and π-electron contributions to the out-of-plane component of NICS (NICSzz) leads to the same qualitative and quantitative conclusions previously obtained by the analysis of the magnetically induced ring current densities. © 2018 The Royal Society of Chemistry. https://pubs.rsc.org/en/content/articlepdf/2018/ra/c8ra01263f

Theoretical studies are essential for the structural characterization of clusters, when it comes to rationalize their unique size-dependent properties and composition. However, the rapid growth of local minima on the potential energy surface (PES), with respect to cluster size, makes the candidate identification a challenging undertaking. In this article, we introduce a hybrid strategy to explore the PES of clusters. This proposal involves the use of a biased initial population of a genetic algorithm procedure. Each individual in this population is built by assembling small fragments, according to the best matching of the Fukui function. The performance of a genetic algorithm procedure. The performance of the method is assessed on the PES exploration of medium-sized Sin clusters (n = 12-20). The most relevant results are: (a) the method converges at almost half of the time used by the canonical version of the GA and, (b) in all the studied cases, with the exception of Si13 and Si16 , the method allowed to identify the global minimum (GM) and other important low-lying structures. Additionally, the apparent deficiency of the proposal to identify the GM was corrected when a Si atom, or other low-lying isomers, were considered to build the clusters. © 2017 Wiley Periodicals, Inc.

A new approach to stabilize compounds containing a planar tetracoordinate carbon (ptC), embedded in aromatic hydrocarbons, is presented herein. This is achieved by using ligands that promote the formation of a 3c–2e σ-bond with the ptC under two conditions: without altering the sp2 hybridization of the aromatic carbons; and containing empty orbitals perpendicular to the aromatic ring to participate in the aromatic π-electronic delocalization.

The purpose of this study is to show that H2 is easily dissociated on lithium edge decorated carbon systems to form strong C–H and Li–H bonds. This mechanism has not been considered in previous studies where these kinds of systems have been proposed as good candidates to serve as hydrogen storage materials. The reactivity of molecular hydrogen (H2) on three representative lithium edge-decorated carbon systems (on the clusters C5Li7+ (1) and C6Li6 (2), and on lithium edge-decorated zig-zag graphene nanoribbon (GNR-Li) (3)) have been studied using ab initio calculations based on the density functional theory with dispersion-corrected van der Waals exchange correlation functional. Our calculations show, on the one hand, that heterolytic hydrogen dissociation can precede with relatively low reaction barriers (0.60, 0.45 and 0.56 eV for systems 1, 2 and 3, respectively) along the minimum energy path and, on the other hand, that chemisorption energies are highly stabilizing (in the range of 1.15–1.54 eV). It is important to note that the highest activation barrier is found for the unique system, characterized as global minimum, on its corresponding potential energy surface (PES), which is system 1. These findings suggest that reversibility of the hydrogen absorption/desorption reactions, required in promising hydrogen storage materials, does not apply in these systems.

The stability, electronic and optical properties of an isomer of B116N124 fullerene were analyzed by using the DFT calculations. The results indicate that the structure is stable and exhibits a high cohesion energy (Ecoh = −7.82 eV/atom). The quantum descriptors of this fullerene revealed: low values for polarity, chemical reactivity and work function, as well as electronic behavior like conductor. According to above features, this system can be considered in electrical, electronic or biological applications. This cluster presents its highest absorption peak around 244–281 nm and it was characterized through the natural transition orbitals showing a π → π* behavior.

Systematic analysis of the noble gas (Ng = He – Rn) trapping capacity of the B12N12 cluster were performed at the PBE0-D3/def2-TZVP level by means of thermochemical data, topological analysis of the electron density (QTAIM), non-covalent interactions index (NCI), and energy decomposition analysis (EDA). The results indicate that the Ng n@B12N12 (n = 1, 12) cluster can be obtained below room temperature. Additionally, it was found that this cluster can trap up to 12 noble gas atoms without losing stability, Finally, the effect of an applied electric field has been analysed, showing that the interaction energy can be improved through this strategy.

A systematic analysis of the photoelectronic properties and aromaticity in meso and beta halogenated expanded porphyrins (Sapphyrin and Orangarin), have been carried out by means of Time Dependent Density Functional Theory (TD-DFT) and magnetic criteria of aromaticity. Results indicate that there is a notorious redshift in the Soret-type (Q-type) bands. The electronic absorption of meso-substituted compounds showed a strong redshift in aromatic porphyrins compared to its beta counterpart and can be attributed to the lower energy gap. For antiaromatic derivatives an inverse trend is observed where beta compounds have a greater redshift than meso compounds. Additionally, major redshifts are observed for the Q bands in iodine-derived compounds. Magnetic aromaticity analysis showed that there is a systematic decrease for aromatic derivatives, following a periodical trend (F to I), whereas a decrease in antiaromaticity for orangarin derivatives is found. Finally, correlations have been found between the energy gaps and Q-type bands of the aromatic porphyrins studied. Halogenation strategy for enhancing the properties in aromatic/antiaromatic porphyrins could be useful in the design of chromophores with potential application in dye sensitized solar cells.

The effectiveness of our proposed approach to stabilize a planar tetracoordinate carbon (ptC) in cyclic aromatic hydrocarbons, introduced in the title article, is unquestionable as our exhaustive searches on the singlet and triplet potential energy surfaces of the new ptC molecules identified as viable species are reproducible. Besides, the T1 diagnostic value for the Si2C5H2 system reported in the comment seems to be the T1 amplitudes. We recomputed the T1 diagnostic value using different software (Gaussian and ORCA), which gave similar values to that reported in our communication. Additionally, a multiconfigurational (complete active space SCF) calculation fully confirms the mono-configurational character of the questioned Si2C5H2 ptC structure. We accept that the linear isomer for the C7H2 system, in the triplet electronic state, is competitive with the isomer reported in our article, in the singlet electronic state, as mentioned in the title comment. However, this is a minor correction that does not affect the primary goal and main conclusions of our communication.

The prediction of reactivity is one of the long-standing objectives of chemistry, contributing to enforce the link between theory and experiment. In particular, the regioselectivity of aromatic molecules has motivated the proposal of different reactivity descriptors based on foundational theories, like Frontier Molecular Orbital (FMO) theory and density functional theory, to predict and rationalize such regioselectivity. This article examines cases where reactivity descriptors, based on FMO theories, are known to have failed, specifically on electrophilic aromatic substitution reactions, through a simple but effective new reactivity model: the Orbital-weighted Fukui function ( fw-(r)) and its topological analysis. Interestingly, this descriptor proves to be effective in adequately predicting regioselectivities where other approximations failed. © 2017 Wiley Periodicals, Inc.

The magnetic aromaticity of 6-membered monoheterocycles containing Group 13 to 16 elements (C5H5X, where X = SiH, GeH, N, P, As, O+, S+, Se+) was assessed by using 2 magnetic descriptors: the π-electron contribution to the out-of-plane component of the nucleus-independent chemical shifts (NICSzz,π) and ring current strength. The results show that both descriptors lead to the same conclusion regarding magnetic aromaticity. However, they do not agree with the predictions obtained by isotropic NICS, which is a most commonly used method. Ring current strength and NICSπ predict that benzene is the most aromatic molecule of the series, with an only slightly less aromatic pyridine. Additionally, aromaticity decreases when going down in the same group of the periodic system. The only exception is the pyrylium cation, which is predicted as the least aromatic species of this series.