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Recently, π–π stacked antiaromatic π‐systems have received considerable attention because they can exhibit stacked‐ring aromaticity due to substantial intermolecular orbital interactions. Here, we report three antiaromatic norcorrole dimers that self‐assemble to form supramolecular architectures through chiral self‐sorting. A 2,2'‐linked norcorrole dimer with 3,5‐di‐tert‐butylphenyl groups forms a π‐stacked dimer both in solid and solution states via homochiral self‐sorting. Its association constant in solution is (3.6±1.7)×105 M−1 at 20 °C. In the solid state, 3,3'‐linked norcorrole dimers with 3,5‐di‐tert‐butylphenyl and phenyl groups afford macrocyclic and helical supramolecular assemblies via heterochiral and homochiral self‐sorting, respectively. Notably, the subtle modification in the substituent resulted in a complete change in the structure of the aggregates and the chiral self‐sorting mode. The present findings demonstrate that structural manipulation in antiaromatic monomer units leads to the formation of various supramolecular assemblies on the basis of the attractive interactions between antiaromatic π‐systems. [ABSTRACT FROM AUTHOR]

Norcorrole Ni(II) complexes have recently received considerable attention because they are readily accessible antiaromatic molecules. Their high stability under ambient conditions and ease of synthesis have enabled the exploration of the intrinsic properties of antiaromatic molecules. Here, we report the synthesis and properties of meso–meso singly linked porphyrin‐norcorrole hybrids and a triply linked porphyrin‐norcorrole hybrid. The singly linked and triply linked porphyrin‐norcorrole hybrids were fully characterized, including an X‐ray structural analysis. Due to their orthogonal conformation, the singly linked hybrids maintain the individual electronic properties of their porphyrin and norcorrole subunits, while the triply linked hybrid shows a significantly smaller electrochemical HOMO–LUMO gap (0.45 eV) than that of Ni(II) dimesitylnorcorrole (1.08 eV). Furthermore, the triply linked hybrid exhibits singlet diradical characteristics, as confirmed by VT NMR, ESR, and SQUID experiments. [ABSTRACT FROM AUTHOR]

Substances containing two π‐congested aromatic systems are attractive targets in synthetic studies as well as efforts designed to explore the unique properties that originate from π‐congestion. Since the time of the computational studies by Schleyer and Warner, the concept of stacked aromaticity created by the encounter of two antiaromatic rings has received much attention. A structure containing π‐congestion between two antiaromatic norcorrole rings was prepared by Shinokubo et al. In contrast, questions about what happens when two aromatic rings are closely stacked have remained unanswered. Specifically, the electronic consequences of stacking of two aromatic π‐conjugated systems have not been fully evaluated. To the best of our knowledge, only one computational study has been performed by Herges, the results of which suggest that [2.2]paracyclophane, possessing short distance (<3.00 Å) between two aromatic ring planes, has a paratropic ring current between two the benzene rings. This observation is consistent with the conclusion that stacked antiaromaticity exists within the π‐congested space between aromatic rings. Herein, we investigated the stacked antiaromaticity of highly π‐congested anthracene dimers using anthracenophane, which possesses a short interplane carbon–carbon distance of ca. 2.80 Å. The absorption spectrum of this substance contains a weak broad band from 450 to 550 nm that is attributed to the HOMO–LUMO transition. These properties exist in planar cyclooctatetraene derivatives that have 8π‐electron antiaromaticity. The results of nucleus‐independent chemical shift and anisotropy of the induced current density calculations indicate that a relatively weak antiaromatic character exists between the central six‐membered rings of the two anthracene moieties in anthracenophane. In addition, an attempt to enhance the stacked antiaromaticity of anthracenophane using pressure to enhance π‐congestion was unsuccessful. [ABSTRACT FROM AUTHOR]

Four difluorenoheteroles having a central quinoidal core with the heteroring varying as furan, thiophene, its dioxide derivative and pyrrole have shown to be medium character diradicals. Solid‐state structures, optical, photophysical, magnetic, and electrochemical properties have been discussed in terms of diradical character, variation of aromatic character and captodative effects (electron affinity). Organic field‐effect transistors (OFETs) have been prepared, showing balanced hole and electron mobilities of the order of 10−3 cm2 V−1 s−1 or ambipolar charge transport which is first inferred from their redox amphoterism. Quantum chemical calculations show that the electrical behavior is originated from the medium diradical character which produces similar reorganization energies for hole and electron transports. The vision of a diradical as simultaneously bearing pseudo‐hole and pseudo‐electron defects might justify the reduced values of reorganization energies for both regimes. Structure‐function relationships between diradical and ambipolar electrical behavior are revealed. [ABSTRACT FROM AUTHOR]

The dianion and dication of tetramesityl‐substituted tetracyclopentatetraphenylene, a circulene consisting of alternating five‐ and six‐membered rings, have been generated by reduction with alkali metals and oxidation with antimony(V) halides, respectively. They are theoretically predicted to adopt double annulenoid structures called annulene‐within‐an‐annulene models in which the outer and inner conjugation circuits are significantly decoupled. The theoretical structures were experimentally proven by X‐ray crystallographic analyses and the electronic configurations were supported by MCD spectra. Based on the 13C NMR chemical shifts, negative and positive charges are shown to be located mainly at the outer periphery, indicating that the dianion and dication have delocalized 22‐π and 18‐π electron outer perimeters, respectively, and 8‐π electron structure at the inner ring. Notably, the dianion has an open‐shell character, whereas the dication has a closed‐shell ground state. [ABSTRACT FROM AUTHOR]

We examine the effects of fusing two benzofurans to s‐indacene (indacenodibenzofurans, IDBFs) and dicyclopenta[b,g]naphthalene (indenoindenodibenzofurans, IIDBFs) to control the strong antiaromaticity and diradical character of these core units. Synthesis via 3‐functionalized benzofuran yields syn‐IDBF and syn‐IIDBF. syn‐IDBF possesses a high degree of paratropicity, exceeding that of the parent hydrocarbon, which in turn results in strong diradical character for syn‐IIDBF. In the case of the anti‐isomers, synthesized via 2‐substituted benzofurans, these effects are decreased; however, both derivatives undergo an unexpected ring‐opening reaction during the final dearomatization step. All the results are compared to the benzothiophene‐fused analogues and show that the increased electronegativity of oxygen in the syn‐fused derivatives leads to enhancement of the antiaromatic core causing greater paratropicity. For syn‐IIDBF increased diradical character results from rearomati‐zation of the core naphthalene unit in order to relieve this paratropicity. [ABSTRACT FROM AUTHOR]

The singlet open‐shell character and antiaromaticity are intriguing features in π‐conjugated carbocycles. These two exhibit similar chemical and physical properties. However, they rarely coexist in the same molecule. Understanding the interrelation between the open‐shell and antiaromatic characteristics in the same molecule is crucial to control the electronic properties. Herein we describe the synthesis and characterization of a new member of diareno[a,f]pentalene, benzo[a]naphtho[2,3‐f]pentalene 6. Unlike its isomer 5 with a closed‐shell ground state, 6 exhibits an appreciable open‐shell character and a moderate antiaromatic feature. The behaviors of the open‐shell index (y0) against the difference of the proton chemical signal (Δδ(H1)) between pentalenide dianions/neutral pentalenes for our reported pentalenes 1, 4, 5, and 6 give a thought‐provoking conclusion about the interrelation between open‐shell and antiaromatic characteristics in this series. The mode of the incorporated quinoidal moiety and the formal molecular symmetry are critical to balance these two characteristics. [ABSTRACT FROM AUTHOR]

Upon photon absorption, π‐conjugated organics are apt to undergo ultrafast structural reorganization via electron‐vibrational coupling during non‐adiabatic transitions. Ultrafast nuclear motions modulate local planarity and quinoid/benzenoid characters within conjugated backbones, which control primary events in the excited states, such as localization, energy transfer, and so on. Femtosecond broadband fluorescence upconversion measurements were conducted to investigate exciton self‐trapping and delocalization in cycloparaphenylenes as ultrafast structural reorganizations are achieved via excited‐state symmetry‐dependent electron‐vibrational coupling. By accessing two high‐lying excited states, one‐photon and two‐photon allowed states, a clear discrepancy in the initial time‐resolved fluorescence spectra and the temporal dynamics/spectral evolution of fluorescence spectra were monitored. Combined with quantum chemical calculations, a novel insight into the effect of the excited‐state symmetry on ultrafast structural reorganization and exciton self‐trapping in the emerging class of π‐conjugated materials is provided. [ABSTRACT FROM AUTHOR]

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Para‐quinodimethane (pQDM) is a fundamental structural component in many π‐conjugated organic molecules and materials. The incorporation of phosphorus atom into π‐conjugated frameworks offers unique opportunities for controlling the properties of derived species. A phosphorus analogue of p‐quinodimethane (pQDM), (IPrC)2P4 [5, IPr=C{N(Ar)CH2}2; Ar=2,6‐iPr2C6H3] featuring a planar P4 ring, was readily accessible by KC8‐reduction of (IPrC)(PCl2)2 (2). Base‐mediated C−H functionalization of IPrCH2 (1) with PCl3 afforded 2. The formation of 5 was expected to occur through a dimerization of the transient 3H‐diphosphirene (IPrC)P2 (4), which was theoretically suggested to have an intermediate diradical character. Compound 5 underwent photo‐induced ring‐contraction reaction to form the singlet diradicaloid (IPrCP)2VI and white phosphorus (P4). The formation of and VI and P4 suggested the formal diphosphorus (P2) elimination from 5. Indeed, photolysis of a mixture of 1,3‐cyclohexadiene (CHD) and 5 led to the formation of P2‐entrapped product (CHD)2P2 (6). The compound 5 represents the first organophosphorus species that functions as a P2 source. Metal‐free P2 transfer: A phosphorus analogue of p‐quinodimethane [(IPrC)2P4] (5, IPr=1,3‐Bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene),was readily accessible through KC8‐reduction of (IPrC)(PCl2)2 (2). The P4 ring of 5 is perfectly planar and embedded with trans‐apical N‐heterocyclic vinylidene ligands. Compound 5 served as a metal‐free diphosphorus (P2) source, which was captured with 1,3‐cyclohexadiene (CHD), giving P2(CHD)2 (6). [ABSTRACT FROM AUTHOR]

The singlet fission (SF) dynamics of pentacene linear aggregate models are investigated using the quantum master equation method by focusing on the Frenkel excitonic (FE) coupling effects on the SF rate and double triplet (TT) yield as well as on their aggregate size dependences. It is found that for the dimer model, unrealistically large FE couplings are needed to provide significant effects on the SF dynamics, while for the larger aggregate models a realistic FE coupling causes significant variations in the SF dynamics: as increasing the aggregate size, the SF rate rapidly increases, attains the maximum at 8‐mer (~3 times enhancement as compared to the non‐FE‐coupling case) and then decreases, approaching a stationary value after 12‐mer, although the stationary TT yield at 20‐mer remains slightly smaller than that in the non‐FE‐coupling case. These features are explained based on the relative relaxation factors between the adiabatic exciton states. The present results contribute to constructing the design guidelines for highly efficient SF aggregates. © 2018 Wiley Periodicals, Inc. The singlet fission (SF) dynamics of pentacene linear aggregates are investigated using the quantum master equation method by focusing on the Frenkel excitonic (FE) coupling effects on the SF rate and double triplet yield as well as on their aggregate size dependences. It is found that a realistic FE coupling causes significant size‐dependent variations in the SF rate, which are explained by the relative relaxation factor analysis. [ABSTRACT FROM AUTHOR]

Two‐fold C−C cross‐coupling of N‐heterocyclic carbenes [NHCs; SIPr=C(NArCH2)2, 1; IPr=C(NArCH)2, 2; Me‐IPr=C(NArCMe)2, 3; Ar=2,6‐iPr2C6H3] with 4,4′′‐diiodo‐p‐terphenyl under Ni catalysis furnished [(SIPr)(C6H4)3(SIPr)](I)2 (4), [(IPr)(C6H4)3(IPr)](I)2 (5), and [(Me‐IPr)(C6H4)3(Me‐IPr)](I)2 (6). Two‐electron reduction of 4–6 with KC8 readily afforded NHC analogues of Müller's hydrocarbon (MH), [(SIPr)(C6H4)3(SIPr)] (7), [(IPr)(C6H4)3(IPr)] (8), and [(Me‐IPr)(C6H4)3(Me‐IPr)] (9), respectively, as highly colored crystalline solids. Quantum chemical calculations suggested that the singlet ground state for 7–9 possesses a vertical singlet–triplet energy gap ΔES‐T of −7.24 to −7.60 kcal mol−1, which is significantly lower compared to that of the NHC analogues of Thiele's (TH) and Chichibabin's (CH) (18–38 kcal mol−1) hydrocarbons. Importantly, the calculated diradical character (y) of 7–9 (y≈0.6) is considerably higher compared to that of the related TH and CH (y=0.1–0.4), suggesting the open‐shell singlet character of 7–9. Radical taming by NHCs. Crystalline N‐heterocyclic carbene (NHC) analogues of the highly reactive Müller's hydrocarbon (A), [(NHC)(C6H4)3(NHC)] (B) are reported [NHC=C(NArCH2)2, SIPr; C(NArCH)2, IPr; C(NArCMe)2, Me‐IPr; Ar=2,6‐iPr2C6H3]. They feature a singlet ground state with small singlet–triplet energy gaps (ΔES‐T≈7.4 kcal mol−1) along with an intermediate diradical character (y=65 %). [ABSTRACT FROM AUTHOR]

Geometric features, electronic structures and third‐order nonlinear optical (NLO) properties of belt‐shaped hydrocarbons, namely, carbon nanobelts, are investigated by using the density functional theory (DFT) methods. A carbon nanobelt composed of five‐ and six‐membered rings (IF‐CNB, 42π), which involves repeating indenofluorene (IF) units, is expected to exhibit both open‐shell multiradical character and relatively strong aromatic nature in the singlet state, while that composed only of six‐membered rings (CNB, 48π) is shown to be a closed‐shell weak antiaromatic species. These features of electronic structure of IF‐CNB are shown to be closely related to its p‐quinodimethane (pQM)‐like substructures and several geometric features (bond‐length alternations and symmetry) of the system. Third‐order NLO properties of open‐shell IF‐CNB is expected to be enhanced more than three times as large as those of the closed‐shell CNB. These results indicate the possibility of further multi‐functionalizations of belt‐shaped hydrocarbons by fusing five‐membered rings. A theoretically designed carbon nanobelt composed of five‐ and six‐membered rings (IF‐CNB, 42π) involving repeating indeno[1,2‐b]fluorene units is found to have a potential for exhibiting open‐shell multiradical character, strong aromatic nature and large third‐order nonlinear optical properties in the singlet state based on broken symmetry density functional theory calculations. [ABSTRACT FROM AUTHOR]

Abstract: The aromaticity of dicyclopenta‐fused acenes (DPAs) and polyacenes (PAs) of increasing size has been studied by evaluation with the GIMIC method at the DFT level of the magnetically‐induced currents (MICs), and by analyzing their spatial distributions. For these open‐shell singlet molecules, spin‐restricted and ‐unrestricted treatments provide very different MICs, the latter ones providing the most reliable solution. These MICs and the differences between spin‐restricted and ‐unrestricted treatments are interpreted in terms of the bond current strengths and the current gradients, which indicate the bond aromaticity and enable the spatial distributions of the diatropic and paratropic currents to be analyzed, respectively. In particular, they allow the rationalization of the MICs in correlation with the odd‐electron density distributions and their diradical characters. These calculations demonstrate that 1) in increasingly large PAs the bond current strengths get smaller and smaller than in benzene and get almost similar in the central and terminal rings, 2) for DPAs the MICs increase from dominant paratropic currents and antiaromaticity in the small compounds to diatropic currents and aromaticity in the larger ones, and 3) in the largest DPAs, the central rings are characterized by large diatropic currents and the terminal five‐membered rings, for which the odd‐electron densities are localized by weak ones. [ABSTRACT FROM AUTHOR]

Abstract: Fused benzene rings to antiaromatic compounds generally improve their stability but attenuate their antiaromaticity. The opposite case is now reported. NiII benzonorcorroles were synthesized and the effect of benzo‐fusion on the antiaromaticity was elucidated. The benzo‐fusion resulted in significant decrease of the HOMO–LUMO gaps and enhancement of the paratropic ring current effect. Furthermore, the introduction of the benzo groups induced singlet diradical character in the antiaromatic porphyrinoid. [ABSTRACT FROM AUTHOR]

Abstract: Tunability of the open‐shell character, charge asymmetry, and third‐order nonlinear optical (NLO) properties of covalently linked (hetero)phenalenyl dimers are investigated by using the density functional theory method. By changing the molecular species X and substitution position (i, j) for the linker part, a variety of intermonomer distances R and relative alignments between the phenalenyl dimers can be realized from the geometry optimizations, resulting in a wide‐range tuning of diradical character y and charge asymmetry. It is found that the static second hyperpolarizabilities along the stacking direction, γyyyy, are one‐order enhanced for phenalenyl dimer systems exhibiting intermediate y, a feature that is in good agreement with the “y–γ correlation”. By replacing the central carbon atoms of the phenalenyl rings with a boron or a nitrogen, we have also designed covalently linked heterophenalenyl dimers. The introduction of such a charge asymmetry to the open‐shell systems, which leads to closed‐shell ionic ground states, is found to further enhance the γyyyy values of the systems having longer intermonomer distance R with intermediate ionic character, that is, charge asymmetry. The present results demonstrate a promising potential of covalently linked NLO dimers with intermediate open‐shell/ionic characters as a new building block of highly efficient NLO systems. [ABSTRACT FROM AUTHOR]

Of the five possible indenofluorene regioisomers, examples of a fully conjugated indeno[1,2- a]fluorene scaffold have so far remained elusive. This work reports the preparation and characterization of 7,12-dimesitylindeno[1,2- a]fluorene as a highly reactive species. Experimental and computational data support the notion of a molecule with pronounced diradical character that exists in a triplet ground state. As such, both NICS and ACID calculations suggest that the indeno[1,2- a]fluorene scaffold is weakly Baird aromatic. Reduction of the unstable red solid with Cs metal produces the dianion of the title compound, from which single crystals could be obtained and X-ray data acquired, thus fully corroborating the proposed indeno[1,2- a]fluorene hydrocarbon core. [ABSTRACT FROM AUTHOR]

The diradical characters ( y) and third-order nonlinear optical (NLO) properties of open-shell quinoidal oligothiophene derivatives with phenoxyl groups, and the corresponding reduced (hydrogenated)-state oligomers, are investigated by using the broken-symmetry density functional theory method. The oxidized (dehydrogenated) states are predicted to have an open-shell singlet ground state and their y values increase with the number of units. Static second hyperpolarizabilities ( γ) of the open-shell oligomers with intermediate y are shown to be enhanced significantly compared with those of the closed-shell analogues. Furthermore, owing to the effective diradical distances, the γ values of open-shell oligomers are found to exceed that of s-indaceno[1,2,3- cd;5,6,7- c′ d′]diphenalene, which is known as an organic molecule with the largest two-photon absorption cross-section in this size of the pure hydrocarbons. This feature extends the range of efficient open-shell third-order NLO materials to a novel class of one-dimensional conjugated oligomers with redox-based high tunability of third-order NLO properties. [ABSTRACT FROM AUTHOR]

A dehydrobenzo[12]annulene attached by three platinum catecholate units is oxidized chemically or electrochemically to generate mono-, di-, and trications. Similarly, a platinum catecholate complex with a dibenzo[8]annulene framework also generates mono- and dications upon oxidation. On the basis of theoretical and spectroscopic studies with respect to energetic, structural, and magnetic criteria, these dications are deduced to be aromatic, thus demonstrating a new method for stabilizing aromatic dications. [ABSTRACT FROM AUTHOR]

Open-shell singlet nature, aromaticity, and second hyperpolarizabilities of two kinds of curved π-conjugated fragments of C60 fullerene, called C60 flakes, together with their corresponding planar analogues are theoretically investigated. It is found that one curved system, A-1, exhibits open-shell singlet nature, while the other structure, B-1, and the two corresponding planar systems possess a closed-shell ground state. The variation of the open-shell singlet nature is explained by the number of Clar's sextets in the resonance structures, which is associated with the local aromaticity, as quantified by the NICS0 values. The calculated orientationally averaged second hyperpolarizabilities show that the open-shell singlet system A-1 exhibits the best performance, and that the other curved system B-1 is the worst among the four C60 flakes, whereas all systems exhibit better performance than the original spherical C60 system. This tendency suggests that a lower dimensionality in the π-conjugated structure is beneficial to the construction of efficient nonlinear optical molecules. The present results not only show that the open-shell singlet system A-1 is a performant nonlinear optical molecule, but they also contribute to a deeper understanding of the electronic structure of curved π-conjugated molecules. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Copyright of Chemistry - A European Journal is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To create a design guideline for efficient third-order nonlinear optical (NLO) molecules, the chain-length ( n) dependences of the diradical character y and the longitudinal second hyperpolarizability γ of quinoidal oligothiophenes (QTs), from monomers to octamers, involving thiophene- S, S-dioxide rings are investigated by using the density functional theory method. It turns out that the diradical character of the modified QTs is reduced as compared to those of the pristine QTs. By introducing an appropriate number of oxidized rings into the QT framework, intermediate y values can be achieved even in the systems with large values of n, in which the pristine QTs are predicted to have pure diradical character. Such intermediate diradical oligomers are shown to exhibit enhanced γ values as compared to the pristine QTs with the same value for n. From the calculation results, the introduction of the optimal number of thiophene-S,S-dioxide rings is predicted to be an efficient chemical modification for optimizing the third-order NLO properties of open-shell QTs through tuning the diradical characters. [ABSTRACT FROM AUTHOR]

The static second hyperpolarizability y of the complexes com-posed of open-shell singlet 1,3-dipole molecule involving a boron atom and a water molecule in aqueous phase are investigated by the finite-field (FF) method combined with a standard polarized continuum model (PCM) and with a newly proposed unbiased PCM (UBPCM). On the basis of the com-parison with the results calculated by the FF method using the full quantum and the quantum-mechanical/molecular-mechanical and molecular-dynamics (QM/MM-MD) treat-ments, the present FF-UBPCM method is demonstrated to remedy the artificial overestimation of the 7 caused by standard FF-PCM calculations and to well reproduce the FF-QM/MM-MD and FF-full-QM results with much lower costs. [ABSTRACT FROM AUTHOR]

Kleiner Lichtabsorber: Das erste Beispiel eines meta ‐ Chinodimethans als Bestandteil eines Indenofluoren ‐ Gerüsts wurde synthetisiert. 10,12 ‐ Dimesitylindeno[2,1 ‐ b]fluoren zeigt eine extrem niederenergetische Absorption, trotz des kleinen konjugierten Systems des Moleküls, das nur 20 π ‐ Elektronen aufweist. [ABSTRACT FROM AUTHOR]

From the viewpoint of 'diradical character,' referred to as 'diradicalology,' we investigate the second hyperpolarizability γ-the molecular third-order nonlinear optical (NLO) property-of one-dimensional supermolecular systems composed of acetylene-linked phenalenyl/pyrene rings using long-range corrected spin-unrestricted density functional theory. It turns out that the pyrene-based superpolyenes (Py- n) behave like closed-shell systems, whereas phenalenyl-based superpolyenes (Ph1- n and Ph2- n) have different diradical characters depending on the linked form, that is, Ph1- n and Ph2- n have intermediate and pure diradical characters, respectively. In comparison with Py- n and Ph2- n, the longitudinal γ of Ph1- n is significantly larger, and it displays larger enhancement as a function of system size. Substitutions to the terminal rings by donor (NH2) and acceptor (NO2) groups further enhance γ in Ph1- n, more than in Ph2- n and Py- n. These results are in agreement with the structure-property relationships derived for open-shell NLO systems with symmetric and asymmetric charge distributions (Nakano et al., J. Chem. Phys. 2010, 133, 154302). © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Using the long-range corrected spin-unrestricted density functional theory method, the impact of antidot structure on the open-shell character and the second hyperpolarizability (γ) of graphene nanoflakes (GNFs) has been investigated for rectangular GNFs with and without antidot structure, referred to as antidot and perfect GNFs, respectively. It is found that the two GNFs exhibit different multiradical characters; the antidot GNF shows intermediate open-shell character in contrast to the perfect GNF presenting nearly pure tetraradical character. This antidot structure dependence of open-shell character can be explained in terms of their natural orbital distributions. Such difference in open-shell characters affects their γ values; the γ of the antidot GNF is about 1.7 times larger than that of the perfect GNF, the feature of which is in agreement with our previous results on the diradical character dependence of γ. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

A long-range corrected spin-unrestricted density functional theory (LC-UDFT) approach has been used to investigate the diradical character ( y i) and third-order nonlinear optical properties of linear/cyclic [ N]acenes and [ N]phenylenes in their ground states, where N is the number of benzene rings in each linear and cyclic configuration. It has been found that linear and cyclic acenes with N = 5-10 show singlet diradical characters, while linear and cyclic phenylenes with equivalent number of benzene rings have closed-shell configurations. The amplitudes of third-order nonlinear optical polarizability (γ zzzz) for open-shell linear/cyclic acenes are larger especially in intermediate range of diradical character than those of closed-shell phenylene counterparts. For example, the γ zzzz values of [5]cyclic acene ( y0 = y1 = 0.320) is 4.89 × 103 a.u. which is about 6 times larger than those of 0.80 × 103 a.u. for closed-shell [5]cyclophenylene. Similarly, γ zzzz value of [5]linear acene is also about 9 times larger than its closed-shell [5]linear phenylene counterpart. Our results show interesting insights into the relationship among the architectures, diradical characters and γ zzzz values of different acenes and phenylenes. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

We developed the quantal cumulant mechanics for treating multidimensional quantum many-body clusters including two-body interaction such as the Morse potential. To evaluate an effective potential appearing in the actual calculation, a Gaussian fitting method was adopted to approximate the Morse potential. The number of the Gaussians that are required to reproduce the total energy of a classical three-dimensional (3D) Morse 3 (M3) cluster is 31, where the error is 10−6. We compared structures of the classical M3 cluster with those of quantum counterpart and found that the quantum structure have broad distribution due to zero point vibration effects. The symmetry of the cluster becomes lower from D3h to D2h by applying the diagonal approximation to the cumulant matrices. Conversely, the original and spherical approximation holds the symmetry constraint. We also perform the same analyses on 2D M4 cluster with two different stable structures, where one has D3h symmetry and the other D2h symmetry. In the latter case, the diagonal approximation accidentally gives the same results as the original one, when two of three Cartesian axes coincide with the cluster symmetric axes. When the cluster rotates with respect to these axes, the results of the diagonal approximation deviate from those by the original one and the artificial symmetry breaking is also found. We also evaluate the optimized structures of the highly symmetric small Morse clusters M n ranging from n = 4-7 and compare with those with the corresponding classical ones. We found that the errors of both the diagonal and spherical approximations in total energy decrease with the number of particles. This fact indicates that these approximations will be useful to investigate static and dynamical properties of many-particle quantum clusters with low computational cost. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

To reveal new structure-property relationships in the nonlinear optical (NLO) properties of fullerenes that are associated with their open-shell character, we investigated the interplay between the diradical character ( yi) and second hyperpolarizability (longitudinal component, γzzzz) in several fullerenes, including C20, C26, C30, C36, C40, C42, C48, C60, and C70, by using the broken-symmetry density functional theory (DFT; LC-UBLYP ( μ=0.33)/6-31G*//UB3LYP/6-31G*). We found that the large differences between the geometry and topology of fullerenes have a significant effect on the diradical character of each fullerene. On the basis of their different diradical character, these fullerenes were categorized into three groups, that is, closed-shell ( yi=0), intermediate open-shell (0< yi<1), and almost pure open-shell compounds ( yi≅1), which originated from their diverse topological features, as explained by odd-electron-density and spin-density diagrams. For example, we found that closed-shell fullerenes include C20, C60, and C70, whereas fullerenes C26 and C36 and C30, C40, C42, and C48 are pure and intermediate open-shell compounds, respectively. Interestingly, the γzzzz enhancement ratios between C30/ C36 and C40/ C60 are 4.42 and 11.75, respectively, regardless of the smaller π-conjugation size in C30 and C40 than in C36 and C60. Larger γzzzz values were obtained for other fullerenes that had intermediate diradical character, in accordance with our previous valence configuration interaction (VCI) results for the two-site diradical model. The γzzzz density analysis shows that the large positive contributions originate from the large γzzzz density distributions on the right- and left-extended edges of the fullerenes, between which significant spin polarizations (related to their intermediate diradical character) appear within the spin-unrestricted DFT level of theory. [ABSTRACT FROM AUTHOR]

The anionic derivative of the pharmaceutical compound 3-methyl-1-phenyl-2-pyrazolin-5-one (MCI-186) is known to deactivate the free radicals in biological systems by donating its excess electron. For the purpose to investigate the mechanism that the MCI-186 anion exhibits the antioxidative activity in aqueous solutions, we have performed a series of quantum mechanical/molecular mechanical (QM/MM) simulations based on the density functional theory in combination with the theory of energy representation (QM/MM-ER). For the computational convenience, MCI-186 has been modeled by 1,3-dimethyl-2-pyrazolin-5-one (DMP) by substituting the phenyl group in MCI-186 by a methyl one. We have applied the QM/MM-ER approach to compute free energy change δ G associated with the electron detachment from DMP anion in water. To make comparisons, we have also performed the simulations for a natural radical scavenger, ascorbic acid modeled by 3,4-dihydroxy-furan-2-one (DHF). In the QM/MM-ER approach, the distribution functions of the solute-solvent interaction energy, which serve as fundamental variables to describe the free energy, are to be constructed with the QM/MM force field. The free energy changes δ G were computed as 99.1, 108.3 kcal/mol for DMP and DHF anions, respectively, whereas that for hydroxyl anion OH taken as a reference system was evaluated as 138.9 kcal/mol. Thus, it was revealed that the free energies δ G for DMP and DHF anions are much smaller than that for hydroxyl anion, which directly indicates the high activities of the molecules as electron donors. We found that the small δ G values can be mainly attributed to the small values in the absolutes of the solvation free energies. The fractional charge analyses provided the evidence that the delocalization of the excess charge on the solute gives rise to the destabilization of these radical scavengers in the solute-solvent interaction. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [ABSTRACT FROM AUTHOR]

Die magnetisch induzierten Ringströme des Außen- und Innenkreises fließen im bzw. gegen den Uhrzeigersinn - ähnlich wie die Züge, die auf der äußeren und inneren Schleife der Osaka Loop Line fahren, wie Ichiro Hisaki, Marina A. Petrukhina, Tohru Nishinaga, Masayoshi Nakano, Yoshito Tobe und Mitarbeiter in ihrem Forschungsartikel berichten (e202115316). Keywords: Annulenes; Circulenes; Dianion; Dication; Tropicity EN Annulenes Circulenes Dianion Dication Tropicity 1 1 1 01/28/22 20220201 NES 220201 B Dianion und Dikation b eines Tetracyclopentatetraphenylenderivats wurden hergestellt und durch Spektroskopie und Röntgenkristallographie charakterisiert. Annulenes, Circulenes, Dianion, Dication, Tropicity. [Extracted from the article]

Keywords: Annulenes; Circulenes; Dianion; Dication; Tropicity EN Annulenes Circulenes Dianion Dication Tropicity 1 1 1 01/28/22 20220201 NES 220201 B Dianion and dication b of a tetracyclopentatetraphenylene derivative were generated and characterized by spectroscopic methods and X-ray crystallography to reveal that the outer and inner conjugation circuits are significantly decoupled as theoretically predicted. Annulenes, Circulenes, Dianion, Dication, Tropicity The magnetically induced ring currents of the outer and inner circuits flow clockwise and counterclockwise, respectively, in the same direction as the trains run on the outer and inner loops of Osaka Loop Line, as reported by Ichiro Hisaki, Marina A. Petrukhina, Tohru Nishinaga, Masayoshi Nakano, Yoshito Tobe, and co-workers in their Research Article (e202115316). [Extracted from the article]

In a previous paper we found that the cofacial intermolecular π–π orbital interaction in stacking dimers significantly changes the longitudinal second hyperpolarizability (γ) of the isolated monomer. On the basis of this result, we investigate the longitudinal γ values of π‐conjugated main chains (CnHn+2, 6 ≤ n ≤ 16) interacting in both‐end regions with two small‐size cationic perturbing π‐conjugated molecules, that is, allyl cations (C3H+5). These interacting model systems exhibit remarkable enhancement of γ values as compared with those of isolated main chains in the whole chain‐length region. The γ density analysis reveals that this enhancement is described by the virtual charge transfer between both‐end perturbing molecules via the main chain. The analysis of orbital correlation diagram between the perturbing molecules and main chain molecule also clarifies that such feature of γ density distribution originates in the “weak intermolecular antibondinglike coupling” between the (lowest unoccupied molecular orbital [LUMO], LUMO+1) of cationic perturbing molecules and (highest unoccupied molecular orbital [HOMO], HOMO−1) of main chain molecule. The current result suggests the possibility of novel nano‐size control of nonlinear optical (NLO) properties by adjusting the intermolecular orbital interactions between the main molecule and perturbing molecules. A possible control scheme of longitudinal γ for novel intermolecular interacting NLO systems using modified DNA wires is also proposed. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [ABSTRACT FROM AUTHOR]

The synthesis of bowl‐shaped antiaromatic molecules is challenging because the molecular distortion further destabilizes these already inherently reactive molecules. Here, we report the synthesis and properties of bowl‐shaped fused anthrylnorcorroles that exhibit near‐infrared (NIR) absorption reaching 1900 nm. The oxidation of meso‐anthryldibromodipyrrin provides fused anthryldibromodipyrrin, which was converted to the fused mono‐ and bisanthrylnorcorroles through Ni(0)‐mediated intramolecular coupling with a bis(dibromodipyrrin) Ni(II) complex. Single‐crystal X‐ray diffraction analyses revealed bowl‐shaped structures for the fused mono‐ and bisanthrylnorcorroles, which enables them to act as suitable receptors for C60 with bonding constants of 2.89×103 M−1 and 1.59×103 M−1, respectively. The formation of a 1 : 1 complex between the fused monoanthrylnorcorrole and C60 was confirmed by single‐crystal X‐ray diffraction analysis. The effective expansion of the π‐conjugation through the triple fusion of the norcorrole with the anthracene units substantially enhances the near‐infrared absorption bands, which endows these anthrylnorcorroles with effective photothermal conversion. [ABSTRACT FROM AUTHOR]

Highlights from the article: Therefore, the magnetically-induced current (MIC) density maps given in Figures 6 and S6 (in the Supporting Information) as well as the nucleus-independent chemical shift (NICS) values given in Figure S5 for the open-shell IF-CNB are found to be those evaluated at the LC-RBLYP/6-311+G** level. In a previous study,[2] on the other hand, we compared the MIC density results from the R- and U-DFT solutions for oligoacenes and dicyclopenta-fused oligoacenes by using the gauge-including MIC (GIMIC) method. Figure shows the side-views of the MIC density map and the integrated values of MIC density for each bond calculated at the LC-RBLYP and LC-UBLYP levels.

The cover picture shows open‐shell and aromatic characters of a theoretically designed carbon nanobelt (CNB) composed of five‐ and six‐membered rings. Quantum chemical calculations and magnetically‐induced current density analysis have revealed that in the presence of repeating indeno[1,2‐b]fluorene (IF) substructures, the IF‐CNB bearing (4n+2)π electrons is expected to exhibit both intermediate open‐shell character and strong aromatic nature. Such features are suitable for applications to third‐order nonlinear optical systems. More information can be found in the Full Paper by Masayoshi Nakano et al. on page 2320 in Issue 11, 2018 (DOI: 10.1002/ajoc.201800390). [ABSTRACT FROM AUTHOR]

The Inside Cover picture shows the drastic change in the third ‐ order nonlinear optical properties of a quinoidal oligothiophENe derivative through the redox reactions in which its electronic structure switches betweEN the closed ‐ shell (lower side) and opEN ‐ shell (upper side) states. More details can be found in the Full Paper by R. Kishi, M. Nakano and co ‐ workers on page   506 in Issue 6, 2017 (DOI: 10.1002/opEN.201700083). [ABSTRACT FROM AUTHOR]

Bond ‐ stretch isomerism is a fundamental concept in chemical bonding. To date, only two isomers, σ ‐ bonded isomers and planar singlet diradicals, have been identified in strained carbon – carbon homolysis. In the present study, the hitherto unknown third isomer, a puckered singlet diradical in the carbon – carbon bonding system of bicyclo[2.1.0]pentane, has been observed experimentally for the first time by careful selection of bulky substituents and using low ‐ temperature spectroscopy, both acting to “freeze frame“ the isomer. More information can be found in the Full Paper by M. Abe, R. Kishi, M. Nakano et al. on page 2299 ff. [ABSTRACT FROM AUTHOR]

10,12 ‐ Dimesitylindeno[2,1 ‐ b]fluoren …︁ …︁ zeigt trotz seines kleinen konjugierten 20π ‐ Elektronensystems eine Absorptionsbande für Licht sehr niedriger Energie, die sich bis 2000 nm erstreckt. Dieses erste Beispiel für ein meta ‐ Chinodimethan in einem Indenofluoren ‐ Gerüst wird von Y. Tobe et al. in der Zuschrift auf S. 6192 ff. vorgestellt. Sie erklären das ungewöhnliche Absorptionsverhalten mit einem partiellen Singulett ‐ Diradikal ‐ Charakter und dem kleinen konjugierten π ‐ System des Kohlenwasserstoffs. [ABSTRACT FROM AUTHOR]

10,12‐dimesitylindeno[2,1‐b]fluorene …︁ …︁ exhibits a very‐low‐energy light‐absorption band that extends to 2000 nm, despite its small conjugation space of only 20 π electrons. This first example of a meta‐quinodimethane embedded in an indenofluorene framework is presented by Y. Tobe and co‐workers in their Communication on page 6076 ff. The unusual absorption behavior is attributed to the moderate singlet biradical character and the small π‐conjugation space of the hydrocarbon. [ABSTRACT FROM AUTHOR]