Diazulenorubicene as a Non-benzenoid Isomer of peri-Tetracene with Two Sets of 5/7/5 Membered Rings Showing Good Semiconducting Properties

Non-benzenoid polycyclic aromatic hydrocarbons (PAHs) have received a lot of attention because of their unique optical, electronic, and magnetic properties, but their synthesis remains challenging. Herein, we report a non-benzenoid isomer of peri-tetracene, diazulenorubicene (DAR), with two sets of 5/7/5 membered rings synthesized by a (3+2) annulation reaction. Compared with the precursor containing only 5/7 membered rings, the newly formed five membered rings switch the aromaticity of the original heptagon/pentagon from antiaromatic/aromatic to non-aromatic/antiaromatic respectively, modify the intermolecular packing modes, and lower the LUMO levels. Notably, compound 2 b (DAR-TMS) shows p-type semiconducting properties with a hole mobility up to 1.27 cm² V⁻¹ s⁻¹. Moreover, further extension to larger non-benzenoid PAHs with 19 rings was achieved through on-surface chemistry from the DAR derivative with one alkynyl group.     

Synthesis and antibacterial activities of novel oxazine and thiazine ring-fused tricyclic quinolonecarboxylic acids: 10-(Alicyclic amino)-9-fluoro-7-oxo-7H-pyrido[1,2,3-de][1,4]benzoxazine-6-carboxylic acids and the corresponding 1-thia congeners

Several analogs 4 and 5 of Ofloxacin ( 1 ) which contain the oxazine and thiazine rings fused with a quinolone carboxylic acid moiety, respectively, were prepared and their in vitro and in vivo antibacterial activities were compared with those of 1 and its previously prepared 3-exo-methylene analogs 2 and 3 . Unlike 1, 2 , and 3 , analogs 4 and 5 possess an antiaromatic oxazine and thiazine moiety and show markedly lower antibacterial activities. Alteration of their C-10 amino-substituent groups from piperazine to azetidine significantly improved the in vitro antibacterial activities, particularly in the case of the thiazine derivative 5 , but not the in vivo ones. The antibacterial activities of these three types of tricyclic quinolonecarboxylic acids are briefly discussed on the basis of the molecular properties revealed by molecular orbital calculation. The molecular dipole moment was suggested to be one possible factor controlling the binding affinity of these compounds with DNA gyrase.     

Characterization of Benzo[a]naphtho[2,3-f]pentalene: Interrelation between Open-shell and Antiaromatic Characters Governed by Mode of the Quinoidal Subunit and Molecular Symmetry

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.     

The role of aromaticity on the building of nanohybrid materials functionalized with metalated (Au(III), Ag(III), Cu(III)) extended porphyrins and single‐walled carbon nanohorns: A theoretical study

An ab initio, systematic study on the aromaticity involving the group of metalated extended porphyrins, termed meso‐hexakis(pentafluorophenyl)‐substituted[26]hexaphyrin(1.1.1.1.1.1) (HP), was performed for the first time. The aromatic behavior of the system shifted to antiaromatic in the [28]HP analogue, due to the presence of hydrogen atoms that break the orbital symmetry. The absorption bands observed in the experiment were assigned to an intraligand charge transfer, where the intrametallic character is also important. The excited states reveal the absorption of visible light and the possibility of electronic transfer to different systems. We propose a system such as single‐walled carbon nanohorns (SWCNHs), due to their special electronic properties, and predict a novel nanohybrid material. The evidence of electronic communication between both species is presented in this work. The HP aromaticity and the spatial configuration of the interaction with SWCNHs are also related to the strength of electronic transfer among the systems, making the HP metalated antiaromatic species and their corresponding nanohybrids potential candidates to be used as building blocks in photovoltaic cell materials. © 2012 Wiley Periodicals, Inc.     

Synthesis,Optical Properties,and Electronic Structures of Tetrakis(pentafluorophenyl)tetrathiaisophlorin Dioxide

The synthesis, structure, optical and redox properties, and electronic structure of tetrakis(pentafluorophenyl)tetrathiaisophlorin dioxide ( 12 ) are reported. Oxidation of tetrakis(pentafluorophenyl)tetrathiaisophlorin ( 11 ) with dimethyldioxirane afforded the oxidized product, which was the tetrathiaisophlorin with two thiophene 1‐oxide moieties ( 12 ). More significant nonplanarity and greater bond length alternation in 12 than those of 11 were observed by X‐ray structural analysis. The absorption spectrum of 12 contains two bands at λ=348 and 276 nm, with a weak tail that extends to λ≈650 nm. Analysis of the magnetic circular dichroism spectrum of 12 , based on Michl's 4N‐perimeter model and molecular orbital calculations, indicate that the broad band at λ=348 nm appears to contain N₂ and P₂ bands, and 12 is classified as a 4nπ system, similar to 11 . The nuclear‐independent chemical shift values and ¹H NMR spectroscopy data indicate that 12 has more antiaromatic character than 11 .     

Synthesis,Crystal Structures,and Properties of 6,12‐Diaryl‐Substituted Indeno[1,2‐b]fluorenes

Fused polycyclic indeno[1,2‐b]fluorene derivatives with aryl substituents at the 6,12‐positions have been prepared as a potential antiaromatic 20π electronic system. They showed strong absorptions in the visible region and amphoteric redox properties. The quinoid‐type molecular structures were revealed by X‐ray crystal‐structure analysis, which indicated that the bond lengths of the quinoid unit depend on the aryl substituents. Whereas nucleus‐independent chemical shift NICS(1) calculations indicate the antiaromatic nature of the s‐indacene core, they have higher stability than substituted acene derivatives. The derivatives with difluorophenyl or anthryl groups were stable in solution. Vapor‐deposited thin films showed ambipolar carrier transportation in the field‐effect transistor devices.     

Trends in geometric and electronic properties of thiophene- and cyclopentadiene-based polymers

In this work, we present theoretical evidence illustrating that cyano derivatives of conducting polymers such as polythiophene, polycyclopentadiene, and polyfulvene have smaller intrinsic band gaps than those of their parent polymers. The geometric and electronic properties of the parent and the derivative polymers were studied with the use of two methodologies: (1) the pseudo-one-dimensional band-structure calculations performed using the semi-empirical molecular orbital theory (MNDO, AM1) and (2) oligomer calculations performed using the ab initio molecular orbital theory both at the Hartree–Fock and configuration interaction levels. In particular, we found that an organic polymer, poly(dicyanomethylene cyclopentadifulvene) (PCNFv), has a comparable (possibly lower) band gap to the one observed in poly(dicyanomethylene cyclopentadithiophene) (PCNTH) (which has a band gap of 0.8 eV). The precursor of PCNFv is poly(dicyanomethylene cyclopentadicyclopentadiene) (PCNCY) in which two cyclopentadiene rings are connected by a dicyanomethylene group. The additional bond conjugation (in contrast to PCNCY) perpendicular to the chain axis makes PCNFv very rigid and fully planar. Trends in structural properties indicate that the lower band gaps in the cyano-substituted polymers, in comparison to their parent polymers, are accompanied by a decrease in bond alternations in the aromatic or trans–cisoid forms and by an increase in bond alternations in the quinoid or cis–transoid forms. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66 : 229–240, 1998     

Dithieno[a,e]pentalenes: Highly Antiaromatic Yet Stable π-Electron Systems without Bulky Substituents

Dithieno[a,e]penalenes (DTPs) with various substituents were synthesized as a class of antiaromatic compounds. Annulation of thiophene rings imparts the pentalene moiety with high thermal stability even without bulky substituents, while retaining antiaromaticity. The higher magnitude of antiaromaticity in DTPs, in addition to the differences in the electronic structures of the fused aromatic rings, resulted in a narrower HOMO–LUMO gap than that of the corresponding dibenzo[a,e]pentalene analog, giving rise to red-shifted electronic absorption that reaches the near-infrared region. Moreover, systematic investigations on the solid-state packing structure revealed that DTPs prefer offset face-to-face packing motifs rather than face-centered π–π stacking. In particular, the thienyl-substituted DTP bearing hydrophilic side chains exhibited thermochromic behavior in polar solvents, which was ascribed to the formation of aggregates.     

FT Raman and DFT Study on a Series of All‐anti Oligothienoacenes End‐Capped with Triisopropylsilyl Groups

Herein, we study the π‐conjugational properties of a homologous series of all‐anti oligothienoacenes containing four to eight fused thiophene rings by means of FT Raman spectroscopy and DFT calculations. The theoretical analysis of the spectroscopic data provides evidence that selective enhancement of a very limited number of Raman scatterings is related to the occurrence in these oligothienoacenes of strong vibronic coupling between collective ν(C?C) stretching modes in the 1600–1300 cm^?1 region and the HOMO/LUMO frontier orbitals (HOMO=highest occupied molecular orbital; LUMO=lowest unoccupied molecular orbital). The correlation of the Raman spectroscopic data and theoretical results for these all‐anti oligothienoacenes with those previously collected for a number of all‐syn oligothienohelicenes gives further support to the expectation that cross‐conjugation is dominant in heterohelicenes. Fully planar all‐anti oligothienoacenes display linear π conjugation which seemingly does not reach saturation with increasing number of annulated thiophene rings in the oligomeric chain at least up to the octamer.     

Macrocyclic Tetraethynylethene Molecular Scaffolding: Perethynylated aromatic dodecadehydro[18]annulenes,antiaromatic octadehydro[12]annulenes,and expanded radialenes

Tetraethynylethene (3,4-diethynylhex-3-ene-1,5-diyne) molecular scaffolding provided access to novel macrocyclic nanometer-sized C-rich molecules with unusual structural and electronic properties. Starting from cis-bis-deprotected cis-bis(trialkylsilyl)protected tetraethynylethenes, the per(silylethynyl)ated octadehydro[12]annulenes 1 and 2 and the corresponding dodecadehydro[18]annulenes 4 and 5 were prepared by oxidative Hay coupling. X-Ray crystal-structure analyses of (i-Pr)₃Si-protected 2 and Me₃Si-protected 4 showed that both annulene perimeters are perfectly planar. Electronic absorption spectral comparisons provided strong evidence that the macro rings in the deep-purple-colored 1 and 2 are antiaromatic (4n π-electrons), whereas those in yellow 4 and 5 are aromatic ((4n + 2) π-electrons). Although unstable in solution, the antiaromatic compound 2 gave high-melting crystals in which the individual octadehydro[12]annulene chromophores are isolated and stabilized in a matrix-type environment formed by the bulky (i-Pr)₃Si groups. Electrochemical studies demonstrated that the antiaromatic octadehydro[12]annulene 2 undergoes two stepwise one-electron reductions more readily that the aromatic chromophore 5 . This redox behavior is best explained by the formation of an aromatic (4n + 2) π-electron dianion from 2 , whereas 5 loses its aromaticity upon reduction. The Me₃Si derivative 4 was deprotected with borax in MeOH/THF to give the highly unstable hexaethynyl-dodecadehydro[18]annulene 6 , a C₃₀H₆ isomer and macrocyclic precursor to a two-dimensional all-C-network. Deprotection of 2 did not give isolable amounts of tetraethynyl-octadehydro[12]annulene 3 due to the extreme instability of the latter. Starting from dimeric and trimeric acyclic tetraethynylethene oligomers, a series of expanded radialenes were obtained. They possess large C-cores with silylethynyl-protected peripheral valences and can be viewed as persilylated C₄₀ ( 7 ), C₅₀ ( 8 ), and C₆₀ ( 9 ) isomers. These expanded C-sheets are high-melting, highly stable, soluble materials which were readily characterized by laser-desorption time-of-flight (LD-TOF) mass spectrometry. Due to inefficient macrocyclic cross-conjugation and/or non-planarity, the extent of π-electron delocalization in 7 – 9 is limited to the longest linearly conjugated π-electron fragment. In agreement with these properties, all three expanded radialenes exhibited similar redox behavior; they are difficult to oxidize but undergo several reversible one-electron reductions in similar potential ranges. Presumably, the reduced π-electron delocalization is also at the origin of the particularly high stability of 7 – 9 .     

An Amphoteric Switch to Aromatic and Antiaromatic States of a Neutral Air‐Stable 25π Radical

Ever since the discovery of the trityl radical, isolation of a stable and neutral organic radical has been a synthetic challenge. A (4n+1)π open‐shell configuration is one such possible neutral radical but an unusual state between aromatic (4n+2)π and antiaromatic (4n)π electronic circuits. The synthesis and characterization of an air‐ and water‐stable neutral 25π pentathiophene macrocyclic radical is now described. It undergoes reversible one‐electron oxidation to a 24π antiaromatic cation and reduction to a 26π aromatic anion, thus confirming its amphoteric behavior. Structural determination by single‐crystal X‐ray diffraction studies revealed a planar configuration for the neutral radical, antiaromatic cation, and aromatic anion. In the solution state, the cation shows the highest upfield chemical shift ever observed for a 4nπ system, while the anion adhered to aromatic nature. Computational studies revealed the delocalized nature of the unpaired electron as confirmed by EPR spectroscopy.     

Fused Indacene Dimers

Polycyclic hydrocarbons consisting of two or more directly fused antiaromatic subunits are rare due to their high reactivity. However, it is important to understand how the interactions between the antiaromatic subunits influence the electronic properties of the fused structure. Herein, we present the synthesis of two fused indacene dimer isomers: s-indaceno[2,1-a]-s-indacene ( s -ID ) and as-indaceno[3,2-b]-as-indacene ( as -ID ), containing two fused antiaromatic s-indacene or as-indacene units, respectively. Their structures were confirmed by X-ray crystallographic analysis. ¹H NMR/ESR measurements and DFT calculations revealed that both s -ID and as -ID have an open-shell singlet ground state. However, while localized antiaromaticity was observed in s -ID , as -ID showed weak global aromaticity. Moreover, as -ID exhibited a larger diradical character and a smaller singlet-triplet gap than s -ID . All the differences can be attributed to their distinct quinoidal substructures.     

A DFT/TDDFT study of porphyrazines and phthalocyanine oxo‐titanium derivatives as potential dyes in solar cells

Density functional theory and time dependent density functional theory calculations at the level of LDA/BP86/TZ2P were performed systematically on several Ti(IV) complexes of porphyrazines and one phthalocyanine. We performed an analysis of the frontier molecular orbitals of the ground state electronic structures and also discuss in particular the good concordance of our results with the experimental data, which affords to predict the geometrical and optical properties of new complexes ( 3 , 4 , and 7 ). We also emphasize the characterization of the UV–vis absorption spectra and propose transitions that contribute to the Q and B bands. Some useful calculated properties in complexes 2 , 3 , and 7 , like: high light absorption in the visible region of the spectra, transitions involved in these bands with a determined direction, charge separation, bigger highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO‐LUMO) gaps than complexes 4 and 5 , and the energy of their LUMO orbitals (that are higher than the lowest energy level of the conduction band of the TiO₂) indicate that system complexes 2 , 3 , and 7 could act as light‐harvesting sensitizers for dye‐sensitized solar cells (DSCs). These proposals were made using a model of the previously experimentally known phthalocyanine, which was used as sensitizer in DSCs devices, comparing its electronic properties with the herein proposed sensitizers. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

AIM and NBO analyses on hydrogen bonds formation in sugar-based surfactants (α/β-d-mannose and n-octyl-α/β-d-mannopyranoside): a density functional theory study

Density functional theory calculations on α/β-d-mannose (α/β-d-Man) and the corresponding glycosides of n-octyl-α/β-d-mannopyranoside (C₈O-α/β-d-Man) were carried out for geometrical optimisation and stability predictions at the B3LYP/6-31G level of theory. These compounds are related anomerically, since they differ by only the orientation of the hydroxyl group at the C1 position. The aim of this study is to investigate the effect of the hydroxyl group's orientations (axial vs. equatorial) at the C1 position on the intra-molecular interactions and the conformational stability of these isomers. The structural parameters of X-H???Y intra-molecular hydrogen bonds were analysed, while the nature of these bonds was considered using the atoms-in-molecules (AIM) approach. Natural bond orbital (NBO) analysis was used to determine bond orders and the effective non-bonding interactions. We have also reported thermodynamic properties and the electronic properties, such as the highest occupied molecular orbital, lowest unoccupied molecular orbital, ionisation energy, electron affinity, electronic chemical potential, chemical hardness, softness and electrophilicity index in the gas phase for all compounds. These results showed that while α-anomers possess only one intra-molecular hydrogen bond, β-anomers possess two intra-molecular hydrogen bonds, which further confirms the anomalous stability of the latter in the self-assembly phenomena.     

1,2,3‐Diazaborinine: A BN Analogue of Pyridine Obtained by Ring Expansion of a Borole with an Organic Azide

A new pathway for the ring expansion reaction of antiaromatic boroles with organic azides is reported. While the reaction usually leads to 1,2‐azaborinines, it was diverted to the formation of a 1,2,3‐diazaborinine by changing the electronic characteristics of the reagents. The isolable azo‐azaborinine intermediate initially formed from the reaction of 1‐(2,3,4,5‐tetraphenylborolyl)ferrocene with 4‐azido‐N,N‐dimethylaniline gradually decomposed to a 1,2,3‐diazaborinine and benzonitrile. Both the spectroscopic properties and the reactivity of the heteroaromatic compound show analogies to pyridine, to which it is isoelectronic. Density functional theory (DFT) calculations provided insight into the mechanism of this unusual transformation.     

Quantum parameters based study of some heterocycles using density functional theory method: A comparative theoretical study

Density functional theory can envisage a vast assortment of molecular possessions such as molecular structures, vibrational frequencies, molecular energies, ionization energies, polar, electric and magnetic properties etc. The efficacy of this method relies on the study of electronic parameters to categorize the reactive sites to comprehend the plausible action of these scaffolds. Further it also facilitates the correlation between the structural characteristics of drug and their inhibition efficiency against infectious microorganisms. In light of the above facts, we have studied the structural parameters such as energy (total), variation of electron density over highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), charge distribution, absolute electronegativity (χ), softness/hardness (σ/ɳ) and fraction of electron transfer (ΔN) of some previously synthesized heterocycles.     

Estimating π binding energy of N‐Heterocyclic carbenes: The role of polarization

In this work, the tuneability of the π acceptor or donor properties of a set of N‐heterocyclic carbenes (NHCs) with a wide spectrum of electronic characteristics is established by means of density functional theory and energy decomposition analysis (EDA) tools. Even though the main orbital interaction contribution to the NHC coordination is the σ donation, a significant contribution of the π interactions to the bond is observed. By means of carefully selected coordination sites, different contributions to the π interactions could be identified and isolated. It includes not only the well known back donation and donation interactions, but also the intrafragment polarization, which has not been considered in previous studies. This can be obtained through the use of the extended transition state method for EDA combined with the natural orbitals for chemical valence and the constrained space orbital variation analysis. The contributions vary with the position of the heteroatoms and the presence of exocyclic substituents; the donation/backdonation π interactions between NHC and the coordination site can range between 2 and 61% of the total π orbital interactions, while the rest is owed to intrafragment polarization. Our results do not only contribute to the understanding of the electronic structure of NHC‐based complexes, giving ways to improve their catalytic properties, but also provide comprehension on the modelization methods used to study their donor–acceptor interactions. © 2015 Wiley Periodicals, Inc.     

Structural,electronic, and magnetoresponsive properties of triangular lanthanide clusters and their free‐standing nitrides

The molecular and electronic structures, stabilities, bonding features, and magnetoresponsive properties of three‐membered [c‐Ln₃]^+/0/? (Ln = La, Ce, Pr, Nd, Gd, Lu) and heterocyclic six‐membered [c‐Ln₃E₃]^q (Ln = La, Ce, Pr, Nd, Gd, Lu; E = C, N; q = 0 or 1) rings have been investigated by means of electronic structure calculation methods at the DFT level. The [c‐Ln₃]^+/0/? clusters are predicted to be bound with respect to dissociation to their constituent atoms, the estimated binding energies ranging from 45.8 to 2056.4 kJ/mol. The [c‐Ln₃] rings capture easily a planar three‐coordinated nitrogen atom at the center or above the center of the ring yielding the lanthanide nitride clusters [c‐Ln₃(μ₃‐N)] adopting a planar geometry, except [c‐La₃(μ₃‐N)] which exhibits pyramidal geometry. The [c‐Ln₃(μ₃‐N)] clusters are predicted to be bound, with respect to dissociation to N (⁴S) atom and [c‐Ln₃] clusters in their ground states, the binding energies ranging from 53.9 to 257.9 kcal/mol. The six‐membered [c‐Ln₃E₃]^q rings are predicted to be bound with respect to dissociation to LnE^q monomers in their ground states with dissociation energies in the range of 173.8 to 318.0 kcal/mol. Calculation of the NICS_zz‐scan curves of the clusters predicted a “hermaphrodic” magnetic response of the [c‐Ln₃]^+/0/? and heterocyclic six‐membered [c‐Ln₃E₃]^q rings, manifested by the coexistence of successive diatropic (aromatic) and paratropic (antiaromatic) zones. The [c‐La₃]^+/0/? and [c‐Lu₃]^? are predicted to be weakly antiaromatic, the [c‐Lu₃]^0/+, [c‐Lu₃C₃]⁺, and [c‐Lu₃N₃] double (σ+π) aromatic, and the [c‐Gd₃C₃] and [c‐Gd₃N₃]⁺ rings (σ+δ)‐aromatic systems. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011     

Preparation,configurational and DFT–NBO analysis of nickel(II) complexes with edta-type ligands containing six-membered backbone ring: crystal structure of [Ni(H2O)6][Ni(1,3-pdta)]·2H2O

New hexadentate nickel(II) complex Mg[Ni(1,3-pd3ap)]·10H₂O containing unsymmetrical edta-type ligand, 1,3-propanediamine-N,N,N′-triacetate-N′-3-propionate (1,3-pd3ap), has been prepared, chromatographically separated, and characterized. Only one [trans(O₅)] of the two possible geometrical isomers was isolated. In this isomer, the two five-membered glycinate rings (R rings) occupy trans-axial sites while the one glycinate ring and one β-alaninate ring lie in the equatorial plane with the two diamine nitrogens (G rings). This result confirms the assignment made on the basis of the density functional theory (DFT), IR, and UV–Vis spectral data analysis. In order to see cation influence on the structural and electronic behavior, [Ni(H₂O)₆][Ni(1,3-pdta)]·2H₂O complex has also been prepared and its structure verified by an X-ray analysis. Spectral data and electronic transition assignment, DFT–natural bonding orbital, and an extensive strain analysis are discussed in comparison with those of other [Ni(edta-type)]^2? complexes of known configuration.