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The photoionization (PI) spectra of small gas-phase yttrium monoxide clusters, YnO (n = 1–8), are investigated, and the adiabatic ionization energies are determined. The stable structures are obtained from density functional theory (DFT) calculations. The ground state structures are further confirmed by the CCSD(T) method. The PI spectra are calculated for these stable structures and are compared with the experimental PI spectra. The ground-state structures of the neutral and cation clusters are experimentally assigned with confidence on the basis of a favourable agreement between the experimental and calculated PI spectra. New structures are proposed for Y2O, Y6O, and Y8O compared to the previous literature. Y2O is a linear molecule in the ground state that was previously proposed as a C2v bent molecule. The YnO clusters become 3-dimensional from n ≥ 3. The O atom stays outside, bridging a triangular face of yttrium clusters. Chemical bonding between the yttrium and oxygen atoms is mostly ionic. The excess charge on the oxygen atom is around 1.4e−, transferred from the yttrium atoms bonded with it. Yttrium atoms are mostly covalently bonded. However, for the bigger clusters, free charges of both polarities appear on yttrium atoms that are not bonded with oxygen, indicating ionic interactions. Frontier orbitals consist of mainly delocalized 4d electrons with some 5s contributions, forming Y–Y bonding interactions, but with little contribution and zero contribution from the oxygen orbitals, regardless of the cluster size. The lost electron of YnO+ mostly comes from the 5s orbitals of all Y atoms in the cluster up to size n = 4, and then from 4d–5s hybrid orbitals from n ≥ 5, with the d contribution increasing with size. This is contrary to the previous view in the literature that photoionization occurs from a localized 4d orbital. [ABSTRACT FROM AUTHOR]

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

A tropylium‐catalyzed carboxylic acid O−H insertion with diazoesters was reported to provide α‐hydroxy esters through an activated carbene intermediate. This study presents a revised mechanism based on density functional theory (DFT) calculations involving a unique homoaromatic intermediate formed between the tropylium ion and the diazoester. The calculated energies of the intermediates and transition states support this revised mechanism. Our computational model explains the tropylium ion's binding to the diazoester, resulting in the homoaromatic intermediate. By comparing the reaction profiles of four different pathways, our findings contribute to a better understanding of the reaction mechanism and have potential implications for designing more efficient catalytic systems. [ABSTRACT FROM AUTHOR]

Fourteen highly reactive isomers of C5H and their ionic counterparts have been theoretically investigated using density functional theory (DFT) and coupled-cluster methods. The linear C5H (l-C5H) radical, pent-1,3-diyn-5-yliden-1-yl (1), along with its cationic form and the cyclic C5H (c-C5H), 1-ethynylcycloprop-1-en-2-yl-3-ylidene (2), have recently been detected in the Taurus Molecular Cloud-1. By using the UCCSD(T)/cc-pCVTZ level of theory, the calculated rotational constants and other spectroscopic parameters are found to be in good agreement with the available experimental data for isomers 1 and 2. Therefore, the current theoretical study may assist synthetic chemists and molecular spectroscopists in detecting other isomers in the laboratory or in the interstellar medium (ISM). Thermodynamically favorable rearrangement schemes for forming low-lying isomers 1, 2, and 3 have also been studied theoretically, and (2λ3-cycloprop-2-en-1-ylidene)ethenylidene (3) with a large dipole moment (μ = 4.73 Debye) is proposed to be a plausible candidate for detection in the ISM. [ABSTRACT FROM AUTHOR]

We investigated the structural and energetic properties of nanoclusters and nanoalloys composed of group 13 elements (B, Al, and Ga) up to a cluster size of 12. We conducted a comprehensive benchmark analysis of density functional and post-Hartree–Fock methods to identify efficient and accurate approaches for studying these systems using our benchmark dataset (BAlGa16) consisting of sixteen dimers and trimers. We compared different density functionals and post-Hartree–Fock methods using bond length and binding energy as parameters. B2PLYP closely follows CCSD(T) for geometry optimization, while REVPBE, BPBE, and PBE show cost-accuracy balanced performances. MRACPF was used as the reference for benchmarking energies, with NEVPT2 being the most accurate method, followed by CCSD(T) and DLPNO-CCSD(T). M06 and range-separated hybrid functionals perform well. Based on a cost-accuracy analysis, we recommend M06/def2-SVP as the preferred method. Additionally, we explored the structural evolution of pure, binary, and ternary clusters of group 13 elements up to 12 atoms, uncovering global and local minima. Ga clusters exhibited more rectangular faces compared to the predominantly trigonal faces of B and Al clusters. Binary clusters showed B in center positions, while Ga preferred outer positions, confirming the higher cohesion of B. The most favorable size of binary clusters (12) exhibited similar compositions of Al and Ga atoms. Compositions with 16.67–40% B, 16.67–60% Al, and 20–50% Ga were estimated to have negative mixing energies, indicating their relative stability. [ABSTRACT FROM AUTHOR]

Simple Summary: Tetra-coordinated carbon-containing molecules generally form tetrahedral carbon geometries. However, there are continuous searches for other possible geometries of tetra-coordinated carbon which are non-classical in nature. However, planar tetra-coordinated carbon (ptC), where all four bonds of the carbon atom are in the same plane or the pyramidane structure in which tetra-coordinated carbon with all four bonds are on the same side of a plane, are good examples of non-classical structures. However, synthesis and experimental realization of these molecules are very challenging in the laboratory. In this paper, we have theoretically investigated nine unusual isomers of the molecular formula C5H4 and studied their stability and novel bonding patterns. One of the ptC compounds has been found to be thermodynamically more stable compared to its tetrahedral counterpart with a high value of dipole moment (μ = 4.64 D), which may be helpful for experimental detection in the laboratory or in the low-temperature regions of the interstellar medium. We have theoretically investigated nine unusual isomers of the molecular formula C5H4 using coupled cluster (CC) and density functional theory (DFT) methods. These molecules possess non-classical structures consisting of two pyramidanes, three planar tetracoordinate carbon (ptC), and four spiro types of isomers. Both the pyramidanes (tetracyclo-[2.1.0.01,3.02,5]pentane; py-1 and tricyclo-[2.1.0.02,5]pentan-3-ylidene; py-2) are minima on the potential energy surface (PES) of C5H4. Among the three isomers containing ptC, (SP4)-spiro [2.2]pent-1-yne (ptC-2) is a minimum, whereas isomer, (SP4)-spiro [2.2]pent-1,4-diene (ptC-1) is a fourth-order saddle point, and (SP4)-sprio[2.2]pent-1,4-diylidene (ptC-3) is a transition state. The corresponding spiro isomers spiro[2.2]pent-1,4-diene (spiro-1), sprio[2.2]pent-1,4-diylidene (spiro-3) and spiro[2.2]pent-4-en-1-ylidene (spiro-4) are local minima, except spiro[2.2]pent-1-yne (spiro-2), which is a second-order saddle point. All relative energies are calculated with respect to the global minimum (pent-1,3-diyne; 1) at the CCSD(T)/cc-pVTZ level of theory. Quantum chemical calculations have been performed to analyze the bonding and topological configurations for all these nine isomers at the B3LYP/6-311+G(d,p) level of theory for a better understanding of their corresponding electronic structures. ptC-2 was found to be thermodynamically more stable than its corresponding spiro counterpart (spiro-2) and possesses a high dipole moment (μ = 4.64 D). The stability of the ptC structures with their higher spin states has been discussed. [ABSTRACT FROM AUTHOR]

The planar pentacoordinate carbon (ppC) atom is theoretically established here in [XC7H2]2+ and [XSi2C5H2]2+, where X = Be and Mg, using density functional theory. Inclusion compounds with alkali and alkaline earth metal ions are identified with the monomer units of tricyclic C7H2 and Si2C5H2 isomers with a planar tetracoordinate carbon (ptC) atom. While all alkali and some alkaline earth metals (Ca2+, Sr2+, and Ba2+) stabilize the ptC isomer in both cases, Be2+ and Mg2+ ions form a bond directly with the ptC atom, thus making it a ppC atom. The theoretical binding energies computed at the PBE0-D3/def2-TZVP level of theory are ∼−9.68, −10.42, −5.85, and −5.47 eV for [BeC7H2]2+, [BeSi2C5H2]2+, [MgC7H2]2+, and [MgSi2C5H2]2+, respectively. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) based calculations have been carried out to explore the potential energy surface (PES) of CSinGe4−n2+/+/0 (n = 1–3) systems. The global minimum structures in the di-cationic states (1a, 1b, and 1c) contain a planar tetracoordinate carbon (ptC). For the CSi2Ge22+ system, the second stable isomer (2b) also contains a ptC with 0.67 kcal mol−1 higher energy than that of the 1b ptC isomer. The global minima of the neutral and mono-cationic states of the designed systems are not planar. The 1a, 1b, and 1c structures follow the 18 valence electron rule. The relative energies of the low-lying isomers of CSiGe32+, CSi2Ge22+, and CSi3Ge2+ systems with respect to the global minima were calculated using the CCSD(T)/aug-cc-pVTZ method. Ab initio molecular dynamics simulations for 50 ps time indicate that all the global minimum structures (1a, 1b, and 1c) are kinetically stable at 300 K and 500 K temperatures. The natural bond orbital (NBO) analysis suggests strong σ-acceptance of the ptC from the four surrounding atoms and simultaneously π-donation occurs from the ptC center. The nucleus independent chemical shift (NICS) showed σ/π-dual aromaticity. We hope that the designed di-cationic systems may be viable in the gas phase. [ABSTRACT FROM AUTHOR]

The density functional theory (DFT) studies on mono- and dichloro derivatives of benzene, naphthalene, B12H(sub 12)(super 2-), four-atom-sharing condensed systems B20H16, and monocarborane isomers are used to compare the variation of relative stability and aromatically between condensed aromatics. The trends in the variation of the relative energies and aromaticity in these two- and three-dimensional systems are similar and the compatibility of the cap and ring orbitals decides the relative stability of CB19H16.

Though search algorithms are appropriate tools for identifying low-energy isomers, fixing several constraints seems to be a fundamental prerequisite to successfully running any structural search program. This causes some potential setbacks as far as identifying all possible isomers, close to the lowest-energy isomer, for any elemental composition. The number of explored candidates, the choice of method, basis set, and availability of CPU time needed to analyze the various initial test structures become necessary restrictions in resolving the issues of structural isomerism reasonably. While one could arrive at new structures through chemical intuition, reproducing or achieving those exact same structures requires increasing the number of variables in any given program, which causes further constraints in exploring the potential energy surface in a reasonable amount of time. Thus, it is emphasized here that an integrated approach between search algorithms and chemical intuition is necessary by taking the C12O2Mg2 system as an example. Our initial search through the AUTOMATON program yielded 1450 different geometries. However, through chemical intuition, we found eighteen new geometries within 40.0 kcal mol−1 at the PBE0-D3/def2-TZVP level. These results indirectly emphasize that an integrated approach between search algorithms and chemical intuition is necessary to further our knowledge in chemical space for any given elemental composition. [ABSTRACT FROM AUTHOR]

Four copper(II)-flavonolate compounds of type [Cu(LR)(fla)] {where LR = 2-(p-R-benzyl(dipyridin-2-ylmethyl)amino)acetate; R = –OMe (1), –H (2), –Cl (3) and –NO2 (4)} have been developed as a structural and functional enzyme–substrate (ES) model of the Cu2+-containing quercetin 2,4-dioxygenase enzyme. The ES model complexes 1–4 are synthesized by reacting 3-hydroxyflavone in the presence of a base with the respective acetate-bound copper(II) complexes, [Cu(LR)(OAc)]. In the presence of dioxygen the ES model complexes undergo enzyme-type oxygenolysis of flavonolate (dioxygenase type bond cleavage reaction) at 80 °C in DMF. The reactivity shows a substituent group dependent order as –OMe (1) > –H (2) > –Cl (3) > −NO2 (4). Experimental and theoretical studies suggest a single-electron transfer (SET) from flavonolate to dioxygen, rather than valence tautomerism {[CuII(fla−)] ↔ [CuI(fla˙)]}, to generate the reactive flavonoxy radical (fla˙) that reacts further with the superoxide radical to bring about the oxygenative ring opening reaction. The SET pathway has been further verified by studying the dioxygenation reaction with a redox-inactive Zn2+ complex, [Zn(LOMe)(fla)] (5). [ABSTRACT FROM AUTHOR]

Research has been conducted on the 1,2-carboranes and dehydrogeno derivatives. The aromaticity and relative stability of these compounds have been investigated in examining the polyhedral system with the bonding disturbed by dehydrogenation and the details are presented.

A phenothiazine-based photoremovable protecting group (PRPG) for single and dual release of carboxylic acids was developed. The change in the oxidation state of the sulfur atom of the phenothiazine PRPG resulted in singlet oxygen generation, rather than photorelease. The difference in the photochemistry between oxygen-free and oxygen-functionalized phenothiazine was investigated and supported by DFT calculations. [ABSTRACT FROM AUTHOR]

Metal nanoclusters are an important class of materials for catalytic applications. Sub nanometer clusters are relatively less explored for their catalytic activity on account of undercoordinated surface structure. Taking this into account, we studied platinum‐based sub nanometer clusters for their catalytic activity for oxygen reduction reaction (ORR). A comprehensive analysis with global optimization is carried out for structural prediction of the platinum clusters. The energetic and electronic properties of interactions of clusters with reaction intermediates are investigated. The role of structural sensitivity in the dynamics of clusters is unraveled, and unique intermediate specific interactions are identified. ORR energetics is examined, and exceptional activity for sub nanometer clusters are observed. An inverse size versus activity relationship is identified, challenging the conventional trends followed by larger nanoclusters. The principal role of atomicity in governing the catalytic activity of nanoclusters is illustrated. The structural norms governing the sub nanometer cluster activity are shown to be markedly different from larger nanoclusters. [ABSTRACT FROM AUTHOR]

Novel organomagnesium crown ether molecules have been computationally characterized using density functional theory (DFT). Monomer units of MgC6 are used as building blocks. Isomers of MgC6H2 have been extensively explored using both DFT and coupled‐cluster methods in the past by some of us. It had been concluded that the seven‐membered ring isomer, 1‐magnesacyclohept‐4‐en‐2,6‐diyne, was the thermodynamically most stable molecule at all levels. Thus, the latter has been used as the building block for designing new organomagnesium crown ethers. Both alkali (Li+, Na+, and K+) and alkaline‐earth (Be2+, Mg2+, and Ca2+) metal ions selective complexes have been theoretically identified. Theoretical binding energies (▵E at 0 K) and thermally corrected Gibbs free energies (▵G at 298.15 K) have been computed for these molecules with MgC6‐6‐crown‐2, MgC6‐9‐crown‐3, and MgC6‐12‐crown‐4 hosts. Higher binding affinity values obtained for Be2+ indicate that these new crown ether molecules could effectively be used for Be2+ encapsulation. [ABSTRACT FROM AUTHOR]

An efficient catalytic reaction featuring epoxide opening and tetrahydrofuran formation through homolytic substitution reactions at C-O and Ti-O bonds is described. The performance of the two key steps of the catalytic cycle is studied and adjusted by modifying the electronic properties of the catalysts by introducing electron-donating or uwithdrawing substituents to the titanocene catalysts.

Structures and energies of X3H3^2-, X3H4-, X3H5, and X3H6+ are investigated theoretically at B3LYP/6-311G(d) level. The global minimum structures of B were not found to be global minima for Al and Ga.

Five mononuclear RuII complexes supported by two pentadentate polypyridyl ligands, N,N‐bis(2‐pyridylmethyl)‐N‐(bis‐2‐pyridylmethyl)amine (N4Py) {[Ru(N4Py)(Cl)](PF6), 1Cl; [Ru(N4Py)(OH2)](PF6)2, 1Aq} and newly designed N‐benzyl‐N‐((6‐(6‐methylpyridin‐2‐yl)pyridin‐2‐yl)methyl)dipyridin‐2‐yl‐methanamine (N2Py‐MeBpy‐Bz) {[Ru(N2Py‐MeBpy‐Bz)(Cl)](PF6)·MeCN, 2Cl·MeCN; [Ru(N2Py‐MeBpy‐Bz)(OH2)](PF6)2·3H2O·MeOH, 2Aq·3H2O·MeOH and [Ru(N2Py‐MeBpy‐Bz)(MeCN)](PF6)2·0.5MeCN·H2O, 2ACN·0.5MeCN·H2O} were synthesized and characterized using different spectroscopic techniques such as UV/Vis, IR, 1D and 2D NMR spectroscopy, and mass spectrometry. The physicochemical properties of complexes 1Cl and 1Aq, and structural analysis of 1Aq were reported by Kojima and co‐workers (Chem. Sci. 2012, 3, 3421–3431). Structural characterizations of 1Cl, 2Cl·MeCN, and 2ACN·0.5MeCN·H2O were done by using single‐crystal X‐ray diffraction analyses. Catalytic water oxidation activities of aqua‐ligated RuII complexes, using CeIV as sacrificial electron acceptor at pH 1, were examined. Complex 2Aq shows higher activity as compared to 1Aq. Electrochemical study suggests that a formal [RuVI=O]4+ species is the active species which triggers the oxidation of water. Mechanistic investigation reveals that O–O bond formation takes place via water nucleophilic attack (WNA) pathway. The deactivation pathway of catalyst 2Aq has also been investigated. It was observed that complex 2Aq lost its water oxidation activity primarily due to ligand degradation via oxidative N‐debenzylation pathway. Chemically driven water oxidation activities of two mononuclear RuII‐aqua complexes supported by pentadentate ligand scaffolds were studied. A mechanism where a formal [RuVI=O]4+ species acts as an active intermediate triggering O–O bond formation via water nucleophilic attack is suggested. Furthermore, an initial side reaction involving oxidative N‐debenzylation leads to deactivation. [ABSTRACT FROM AUTHOR]

Abstract: HCN oligomerization is considered to be one of the important pathways in chemical evolution. Nucleobases, aminoacids, and many other complex organic molecules can evolve through this pathway. We report an explorative study based on an automated reaction search method that avoids the cognitive bias present when searching chemical reaction space. We discuss the chemical space of the HCN dimer in detail, and the important trimers and tetramers are discussed briefly. A component‐wise molecular‐fingerprint‐based methodology is proposed to identify molecular similarity. We present four different thermal routes to cis/trans‐2,3‐diaminomaleonitrile and 4‐amino‐1H‐imidazole‐5‐carbonitrile, which are important intermediates in prebiotic chemistry. [ABSTRACT FROM AUTHOR]

In this paper, we present fluorescent photoremovable protecting groups (FPRPG) based on bis-acetyl carbazole for the release of two different functional groups such as carboxylic acids, alcohols, thiols, and amines in a sequential fashion. Dualarm caged bis-acetyl carbazoles with different combinations of two unlike functional groups were synthesized. Photophysical studies showed that caged bis-acetyl carbazoles are blue fluorescent and their emission properties are sensitive to the environment. Sequential photorelease of two different functional groups by bis-acetyl carbazole was analyzed by HPLC, UV and emission spectroscopy. The mechanism of the dual release by bis-acetyl carbazole was investigated and supported by TD-DFT calculations. To demonstrate the applicability of the dual release ability of bis-acetyl carbazole FPRPG, we synthesized a drug delivery system (DDS) in which one arm of bis-acetyl carbazole is linked to the carboxylic functional group of chlorambucil (CBL) and the other arm is attached to the hydroxyl group of ferulic acid ethyl ester (FAEE). In vitro studies showed that our DDS presents excellent properties such as photoregulated dual drug delivery, cellular uptake, and biocompatibility. [ABSTRACT FROM AUTHOR]

Modern day computational chemistry is moving towards studying complex chemical systems, and global optimization algorithms are becoming increasingly important in successfully carrying out such studies. Herein, we report on a simple tabu-based strategy that generates sufficiently dissimilar trial structures for subsequent optimization, in which the minimum degree of similarity between initial trial structures is a user-definable parameter. This versatile tabu-based strategy was implemented for modeling aggregation as well as chemical reactions. The method was validated on molecular aggregates of water, CO 2 , and acetic acid, and was successful in finding the global minima and several of the important low-lying minima on the potential energy surface. This strategy was further extended to the efficient generation of trial geometries as applied to chemical reactions, and was validated by predicting the products of binary reactions using a set of 10 Diels-Alder reactions in the gas-phase. After the successful validation, our method was applied to the prediction of various products of Diels-Alder reactions on graphene models. [ABSTRACT FROM AUTHOR]

Following the report of the ferrocene structure, metal complexes containing the heteroatom-substituted cyclopentadienyl (Cp) analogue, that is the η5 pyrrolyl ligand, have been reported. While the Cp ligand continues to be a favorite ligand in organometallics, the transition metal chemistry of the pyrrolyl ligand is still in the developing stage. In view of this, we carried out the reaction between the multidentate ligand 2,3,4,5-tetrakis(3,5-dimethylpyrazolylmethyl)pyrrole (LH) and Mo(CO)6 or [W(CO)3(CH3CN)3] and isolated two new binuclear tricarbonyl Mo(0) and W(0) complexes, [Mo2(CO)6(μ–η2:η2-LH-κ4N)] (1) and [W2(CO)6(μ–η2:η2-LH-κ4N)] (2). Their X-ray structural analyses showed that the metal centers are bridged by the double bonds of the central pyrrole ring (μ–η2:η2), a rarely observed coordination mode. Interestingly, complex 1 is a catalyst precursor for the hydroamination reactions of phenylacetylene with a series of secondary amines at room temperature offering the regioselectively formed anti-Markovnikov product in excellent yields. In addition, DFT calculations were performed to understand the bonding nature of the pyrrole ring in 1 and 2 and to estimate the energy of six different conformations of LH. [ABSTRACT FROM AUTHOR]