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A new series of macrocyclic Ni (II) complexes having indolenine and dibenzotetraaza [ 14 ] annulene (DBTAA) moieties were synthesized and tested for their application as sensitizers in dye - sensitized solar cells (DSSCs). The structures are furnished with anchoring groups of ethyl ester (8a, 8b, and 8c) or carboxylic acid (9c) on the indolenine moiety and hexyloxy (8b) or neopentyloxy (8c, 9c) groups on the DBTAA moiety. The best performance was exhibited by dye 9c, which under constant AM 1.5G solar simulation (100 mW cm−2) using I−/I3− electrolyte gave a short-circuit current Jsc = 0.43 mA cm−2, an open-circuit voltage Voc = 0.41 V and a fill factor FF = 0.528, corresponding to an overall conversion efficiency of η = 0.093%. This is the first investigation of macrocyclic DBTAA derivatives as sensitizers for DSSCs applications.

Summary Annulenes and their charged analogs play an important role in validating Huckel's aromaticity rule. Whereas annulenes with [4n + 2] π electrons tend to delocalize π electron density, annulenes with [4n] π electrons prefer to form local double bonds (bond alternation) resulting in two interconvertible valence isomers. However, it is very challenging to experimentally detect such a valence tautomerization process as a result of the very fast conversion. In this work, we synthesized a series of [n]cyclo-para-biphenylmethine macrocycles ([n]CPBM-An, n = 3–8) as analogs of [n]annulenes and observed the unusual valence tautomerization process by variable-temperature NMR measurements for [4]CPBM-An, which showed a moderate interconversion barrier (11.22 kcal/mol at coalescence temperature) via a C4 tetraradicaloid transition state. These macrocycles showed [n]annulene-like geometries but with unique open-shell polyradical character. Their optical, electrochemical, and magnetic properties were systematically investigated and compared with those of the recently studied [n]cyclo-para-phenylenes.

Monolayers of two-dimensional polymers (2DP) offer an ideal system in the scope of application, as their electronic properties can be tuned at the molecular level. One of the key challenges in to insure a 2DP synthesis quality at the large scale. Here we calculate Raman and infrared (IR) spectra of recently proposed new two-dimensional semiconductor material based on the molecular structure of Thiophene-Tetrathia-Annulene (TTA) and compare it with an isolated single TTA molecule and a dimer. Significant transformation of Raman and IR spectra of individual TTA molecules during transition to a 2D layer was observed. The calculations evidence the possibility of use Raman and IR spectroscopy as an efficient and reliable tool for synthesis and quality control of TTA-2D layer at the large scale.

It has been reported that benzo [7]annulen-7-amines bearing electron withdrawing substituents such as 3d with a 2-Cl or 3e with a 2-NO2 moiety show very high affinity towards the ifenprodil binding site of GluN2B subunit containing NMDA receptors. Therefore, bioisosteres of 3 with an electron deficient pyridine ring instead of the chloro- or nitrobenzene ring were envisaged. Starting from pyridine-2,3-dicarboxylic acid (5) a five-step synthesis of the key intermediate, the ketone 10, was developed. Reductive amination with various primary amines and NaBH(OAc)3 led to the homologous secondary amines 11a-c. Subsequent methylation yielded the tertiary amines 12b and 12c. Receptor binding studies with [3H]ifenprodil revealed Ki-values above 100 nM for the most active phenylpropyl- and phenylbutylamines 11b and 11c. The >100-fold reduced GluN2B affinity of pyridines 11b and 11c compared to the GluN2B affinity of the corresponding chloro- and nitrobenzene derivatives 3d and 3e indicates that the pyridine ring is not tolerated as bioisosteric replacement of the chloro- or nitrobenzene ring in this type of compounds.

Summary π-Conjugated molecules with an annulene-within-an-annulene (AWA) super-ring structure have been pursued by chemists for a long time but with limited success. Here, we report the synthesis of two stable cyclopenta-ring-fused oligo( m -phenylene) macrocycles, 8MC-M and 10MC-M , both showing moderate polyradical character. The octaradicaloid 8MC-M exhibits a [24]annulene-within-[32]annulene structure, which is globally aromatic despite the fact that it possesses 4 n π-electrons. Theoretical analyses reveal that the π-electrons in the inner and outer rings follow Baird's rule such that both are triplet biradicals, and overall the molecule is a ground-state spin singlet. The decaradicaloid 10MC-M also possesses a super-aromatic AWA structure with 30 and 40 π-electrons in the inner and outer rings, respectively. However, it has a triplet ground state with a singlet inner ring satisfying Huckel's rule and a triplet outer ring following Baird's rule. Therefore, molecules with a decoupled AWA super-ring structure are eventually attained and also show unusual global aromaticity.

Despite the difficulty in administering a safe dose regimen and reports of emerging resistance, warfarin (1) remains the most widely-used oral anticoagulant for the prevention and treatment of thrombosis in humans globally. Systematic substitution of the warfarin phenyl ring with either 1,3,5,7-cyclooctatetraene (COT) (2), cubane (3), cyclohexane (4) or cyclooctane (5) and subsequent evaluation against the target enzyme, vitamin K epoxide reductase (VKOR), facilitated interrogation of both steric and electronic properties of the phenyl pharmacophore. The tolerance of VKOR to further functional group modification (carboxylate 14, PTAD adduct 15) was also investigated. The results demonstrate the importance of both annulene conferred π-interactions and ring size in the activity of warfarin.

A newly designed carbocyclic pseudo Troger's base diamine (CTB) monomer, 2,8-dimethyl-3,9-diamino-5,6,11,12-tetrahydro-5,11-methanodibenzo[a,e][8]annulene (CTBDA) and its isomeric analogue 2,8-dimethyl-(1,7)(4,10)(3,9)-diamino-5,6,11,12-tetrahydro-5,11-methanodibenzo[a,e][8]annulene (iCTBDA), were designed for the synthesis of microporous 6FDA-based polyimides (6FDA-CTBDA and 6FDA-iCTBDA). Both polyimides were soluble, exhibited excellent thermal stability of ∼490 °C, and had high surface areas of 587 m2 g−1 (6FDA-CTBDA) and 562 m2 g−1 (6FDA-iCTBDA). A 6FDA-based polyimide derived from 4,10-dimethyl-3,9-diamino-6H,12H-5,11-methanodibenzo[b,f][1,5]-diazocine (6FDA-TBDA) was made for comparison to investigate the effects of the basic tertiary nitrogen functionality in the Troger's base diamine on the polymer properties relative to the carbocyclic 6FDA-CTBDA analogue. 6FDA-TBDA displayed lower gas permeabilities but moderately higher gas-pair permselectivities than 6FDA-CTBDA. The enhanced permselectivity of 6FDA-TBDA resulted exclusively from higher diffusion-based selectivity. Direct gas sorption measurements demonstrated that the basicity in the Troger's base bridge moiety enhanced the sorption capacity of CO2 only slightly and had no effect on the CO2/CH4 solubility selectivity in 6FDA-TBDA vs. 6FDA-CTBDA.

In this issue of Chem, Jishan Wu and colleagues provide the first examples of annulene-within-an-annulene (AWA) structures in which the inner and outer conjugated circuits are formally fully decoupled. Existing models of AWA aromaticity might need to be revised to account for the exceptional behavior of these novel structures.

In this study, the carbonylative sonogashira coupling reaction was performed in the presence of CO (2 MPa) and Nitmtaa@DFNS as NPs. Nickel(II)dibenzotetramethyltetraaza[14]annulene complex (Nitmtaa) prepared and immobilized on amino-fucntionnalized DFNS (N-DFNS) via Ni N (NH2) bond to obtain a stable and reusable new nanocatalyst named as Nitmtaa@DFNS. Good to superb performance products were provided deploying Nitmtaa@DFNS nanocatalyst. In addition, the anatomy of Nitmtaa@DFNS has been distinguished by various methods, including XRD, VSM, FT-IR, SEM, EDX, TEM, and TGA. In addition, the hot filtration test provided complete insight into the heterogeneity of the catalyst. The reuse and recycling of the catalyst were repeatedly investigated for coupling reactions. In addition, the mechanism of the coupling reactions was thoroughly studied.

We have studied the self-assembly structure of meso-diphenyltetrathia [22]-annulene [2,1,2,1] (DPTTA) on highly oriented pyrolytic graphite (HOPG), Au(111), and single-layer graphene (SLG) modified Au(111) substrates. High resolution scanning tunneling microscopy (STM) reveals that DPTTA molecules pack into one dimensionally ordered row structure on graphene and HOPG surfaces, while assemble into two dimensional close-packed structure on Au(111) surface. We ascribe this difference to the effect of the substrate. The addition of C60 molecules on these DPTTA modified substrates further reveals that the structural difference in DPTTA adlayer can affect its ability to form donor-acceptor (D-A) hierarchical structure with C60 molecules. The results provide an example of substrate effect in self-assemblies of functional molecules, which is significant for the design of molecular based devices.

We previously reported a novel Au-catalyzed sequential activation of two different propargyl carboxylates to 6-methylene-6H-benzo[7]annulene-5,8-diyl dicarboxylates. This reaction has been extended to syntheses of highly functionalized 2,2′-bibenzo[7]annulenes with four biphenyls bearing two sets of different propargyl carboxylates.

In this study, the adsorption characteristics together with the modified thermomechanical properties of stable BxCyNz heteronanotubes, i.e. BC2N, BC3, and NC3, in ambient conditions have been explored under the adsorption of NiTMTAA molecules (NiTMTAA/heteronanotube). Employing molecular dynamics study, it is observed that π-π stacking interaction plays a major role in the adsorption of NiTMTAA. The radius of gyration and circumferential distribution along the axis of NTs demonstrate the higher agglomeration of molecules near the wall of CNT and BC3 than that of other NTs. Moreover, it is observed that CNT and BNNT possess the highest Young’s modulus and thermal conductivity than those of heteronanotubes. According to the results, the adsorption of NiTMTAA molecules reduces thermal conductivity. Unlikely, Young’s modulus of NiTMTAA/heteronanotubes for small weight percentage of NiTMTAA molecules (

Herein, we report a general, efficient and solvent-free method for the one-pot synthesis of allylic esters via dehydrogenation of unactivated alkanes and subsequent oxidative cross coupling with different substituted carboxylic acids. A simple, well defined and air stable Cu(II)-complex, [Cu(MeTAA)], featuring a tetraaza-macrocyclic ligand (tetramethyltetraaza[14]annulene (MeTAA)) is used as the catalyst. A wide variety of substituted allylic esters were synthesized in high yields starting from readily available starting materials. Control reactions were carried out to understand the reaction sequence and the plausible mechanism.

A novel (Z)-2,8-dibromo-9-(bromomethylene)-3,5,5-trimethyl-6,7,8,9-tetrahydro-5H-benzo [7] annulene was synthesized by bromination with N-Bromosuccinimide (NBS) of Aryl-Himachalene. The product of this reaction was characterized by 13C NMR, 1H NMR, FT-IR spectroscopy and single crystal X-ray diffraction. In the solid state, the molecules are associated by Br⋯Br halogen bonds, C–H···π interactions and C–H⋯Br hydrogen bonds. The optimized structure parameters of the studied molecule was determined theoretically using density functional theory (DFT/B3LYP) method 6-31 + G(d, p) basis set, and compared with previously reported experimental findings. Calculated chemical shift values and vibrational wavenumbers showed good agreement with the experimental data. The electronic properties, such as HOMO and LUMO energies, and molecular electrostatic potential (MEP) are also performed.

In this study, the impact of one or two hydroxy moieties at the benzo[7]annulene scaffold on the GluN2B affinity and cytoprotective activity was analyzed. The key intermediate for the synthesis of OH-substituted benzo[7]annulenamines 11–13 and 17 was the epoxyketone 8. Reductive epoxide opening of 8 resulted with high regioselectivity in the 5-hydroxyketone 9 (Pd(OAc)2, HCO2H, phosphane ligand) or the 6-hydroxyketone 10 (H2, Pd/C), whereas hydrolysis in aqueous dioxane led to the dihydroxyketone 14. Reductive amination of these ketones with primary amines and NaBH(OAc)3 afforded the benzo[7]annulenamines 11–13 and 17. In receptor binding studies 5-OH derivatives 11 and 12 showed higher GluN2B affinity than 6-OH derivatives 13, which in turn were more active than 5,6-di-OH derivative 17a. The same order was found for the cytoprotective activity of the ligands. The tertiary amine 12a with one OH moiety in 5-position represents the most promising GluN2B negative allosteric modulator with a binding affinity of Ki = 49 nM and a cytoprotective activity of IC50 = 580 nM. In the binding pocket 12a shows a crucial H-bond between the benzylic OH moiety and the backbone carbonyl O-atom of Ser132 (GluN1b). It was concluded that a 5-OH moiety is essential for the inhibition of the NMDA receptor associated ion channel, whereas a OH moiety in 6-position is detrimental for binding and inhibition. An OH or CH2OH moiety at 2-position results in binding at the ifenprodil binding site, but very weak ion channel inhibition.

The present article describes a DFT study of dibenzotetraaza[14]annulene complexed with first row transition metals (M II (DBTAA)), employing calculations made using the B3LYP hybrid functional with the Lanl2DZ/6-31G ∗ basis set. The parameters considered were bond distances and angles, electron configurations, interaction energies, vibrational frequencies, and frontier molecular orbitals (HOMO and LUMO). The calculations indicated that the key to complexes of the metals Ti, and Cr was the high spin state, while for Mn and Fe it was the intermediate spin state and for Co, Ni, Cu, and Zn it was the low spin state. The M–N distance (d(M–N)) and vibrational frequency showed inversely proportional behavior as a function of the atomic number of the metal. The Ni(DBTAA) complex showed the smallest d(M–N) and highest vibrational frequency, indicating greater compaction of the ligand on nickel. The interaction energy and the gap (HOMO–LUMO) were also calculated in order to estimate the stability and reactivity of the complexes. The stability increased with the atomic number of the central metal, in agreement with the Irving–Williams series, with Ni(DBTAA) being the most stable, and Ti(DBTAA) and Mn(DBTAA) being the most reactive of the complexes investigated.

The novel aromatic heteromacrocycle, p-bromophenyl substituted tetrathia[22]annulene[2,1,2,1] was synthesized as a convenient derivable building block to obtain a variety of tetrathia[22]annulene[2,1,2,1] derivatives, which were recently found to be promising p-type semiconducting materials for OFETs with some unique properties. Furthermore the annulene itself was found to perform well as an active material in OFETs. A thin film transistor based on the annulene had the best hole mobility of 0.73 cm2V−1s−1 and the on/off ratio of 1.4 × 107, which are class leading amongst the macrocyclic field-effect materials.

Novel conjugated macrocycles, thiophene-substituting tetrathia[22]annulenes[2,1,2,1] (TTAs, and 5b), were synthesized through a convenient four-step procedure. They were evidenced to have high aromaticity by NMR, UV–vis absorption spectra, and calculation. Their UV–vis absorption spectra, thermal stability, electrochemical properties, thin film morphology were studied and the field-effect transistors based on 5a and 5b through a vapor deposition method performed good with reproducible bulk-like carrier mobilities (as high as 0.53 cm2 V−1 S−1) and high on/off ratios (as high as 9.0×105), which was among the best records in this series.

Two alternative interpretations are given for the electronic ground state of bis-η8-annulene[8] cerium, cerocene, based on the same relativistic Douglas–Kroll–Hess complete active space all-electron wavefunction. Rotations in the spaces of the one- and many-electron wavefunctions, leaving the total energy invariant, show that the system can be viewed as a complex of a closed-shell Ce(IV) ion sandwiched by two aromatic annulene[8] dianions and bonded with a significant Ce 4f – ring π covalency, or as a Ce(III) ion with an almost atomic-like 4f1 subconfiguration, coupled to the unpaired electron in the rings highest energy occupied π orbitals in a Kondo-type fashion.

A new Co (II) complex of 6,13-disubstituted 1,4,8,11-tetraaza[14]annulene derivative has been synthesized by template condensation reaction of 2-(1-quinolinium-1-yl) trimethinium salt (B) with 1,2-diaminopyridine in the presence of Co (II) acetate in DMF. The electrochemical behavior of the metal complex showed a CoII/CoI redox couple at about −0.99 V vs. Ag/Ag+ in DMF solvent. Axial ligation of N-donor ligands such as pyridine and imidazole was found to shift the reduction potential of CoII/CoI to more negative potential. The binding of N-donor axial ligands to the metal complex was monitored by measuring changes at about 458 nm (maximun absorption of the metal complex) and shifts in the CoII/CoI redox couple potential upon addition of various concentrations of the N-donor axial ligand. Results showed that the number of axial ligand molecules bound to the metal complex is ≈1 and the oxidized state of cobalt (CoII) is more stabilized than the reduced state (CoI) in the presence of the axial ligand. The metal complex also showed catalytic activity toward hydrogen peroxide decomposition in the presence of the N-donor axial ligand.

This paper presents a theoretical study using density functional theory (DFT) to investigate the bonding between carbon monoxide (CO) molecules and type FeN4 macrocycle complexes of iron to form FeN4–CO adducts. In order to understand how different macrocycle ligands affect this interaction, CO molecules were bound to the following complexes: iron–porphyrin (FeP), iron–tetraaza[14]annulene (FeTAA), iron–tetramethyl-tetraaza[14]annulene (FeTMTAA), iron–dibenzotetraaza[14]annulene (FeDBTAA), and iron–tetramethyl-dibenzotetraaza[14]annulenes (FeTMDBTAA1, FeTMDBTAA2). The best description of the systems investigated was provided by the Lanl2TZ(f)/6-31G⁎ basis set, which was therefore used throughout the work. Analysis of the factors influencing the CO bonding process showed that different macrocycle ligands produced adducts that were different in terms of CO bond length, total CO fragment charge, CO vibrational frequency, and CO bond order. The activity of the interaction between CO and the iron-complex was inversely proportional to the energy gap between the HOMO of the FeN4 complex and the LUMO of CO. Finally, a greater degree of back-bonding was characterized by increased occupancy of the px and py orbitals of the O atom of the CO fragment, confirming that the TAAs were more active than porphyrin, in the ascending order: FeP

Diversely functionalized, fused aryl-alkyl ring systems hold a prominent position as well-established molecular frameworks for a variety of anti-cancer agents. The benzosuberene (6,7 fused, also referred to as dihydro-5H-benzo[7]annulene and benzocycloheptene) ring system has emerged as a valuable molecular core component for the development of inhibitors of tubulin assembly, which function as antiproliferative anti-cancer agents and, in certain cases, as vascular disrupting agents (VDAs). Both a phenolic-based analogue (known as KGP18, compound 39) and its corresponding amine-based congener (referred to as KGP156, compound 45), which demonstrate strong inhibition of tubulin assembly (low micromolar range) and potent cytotoxicity (picomolar range for KGP18 and nanomolar range for KGP156) are noteworthy examples of such benzosuberene-based compounds. In order to extend the structure-activity relationship (SAR) knowledge base related to benzosuberene anti-cancer agents, a series of eleven analogues (including KGP18) were prepared in which the methoxylation pattern on the pendant aryl ring as well as functional group incorporation on the fused aryl ring were varied. The synthetic approach to these compounds featured a sequential Wittig olefination, reduction, Eaton's reagent-mediated cyclization strategy to achieve the core benzosuberone intermediate, and represented a higher-yielding synthesis of KGP18 (which we prepared previously through a ring-expansion strategy). Incorporation of a fluorine or chlorine atom at the 1-position of the fused aryl ring or replacement of one of the methoxy groups with hydrogen (on the pendant aryl ring of KGP18) led to benzosuberene analogues that were both strongly inhibitory against tubulin assembly (IC50 approximately 1.0 μM) and strongly cytotoxic against selected human cancer cell lines (for example, GI50=5.47 nM against NCI-H460 cells with fluoro-benzosuberene analogue 37). A water-soluble phosphate prodrug salt of KGP18 (referred to as KGP265, compound 44) and a water-soluble serinamide salt (compound 48) of KGP156 were also synthesized and evaluated in this study.

Meso-phenyl hexaphyrin is an extended annulene system which can adopt both Hückel and Möbius topologies based on the oxidation state. In this contribution we analyze the remarkable sign inversion of the MCD spectrum which accompanies this topological switch. The treatment is based on the identification of the circular wave assignments of the relevant excited states ; the corresponding magnetic moments are calculated using the CASCI (4, 4) approach. In this approach wavefunctions are obtained from configuration interaction in the active space of the four Kohn–Sham frontier orbitals of the chromophore. The results reproduce the signs of the MCD spectra. The anomalous sign in the Möbius conformation is attributed to the quenching of the excited state orbital moment by the ring twist.

The noncovalent functionalization of carbon nanotubes (CNTs) with aromatic polyazamacrocyclic compounds, based on π–π-interactions, keeps the intrinsic electronic structure of CNTs totally intact and allows for combining unique properties of the two interacting components. In addition to porphyrins and phthalocyanines, there are other, simpler compounds exhibiting similar properties, potentially useful for photovoltaic, catalytic and electrochemical applications: for example, tetraaza[14]annulenes. Many of them are highly thermally stable, which makes it possible to employ physical vapor deposition for the preparation of macrocycle–nanotube hybrids. One of such compounds is Ni(II) complex of 5,7,12,14-tetramethyldibenzo-1,4,8,11-tetraazacyclotetradeca-3,5,7,10,12,14-hexaene (also called Ni(II)-tetramethyldibenzotetraaza[14]annulene, or NiTMTAA for simplicity). In the present work, we attempted the noncovalent functionalization of both single-walled and multi-walled CNTs with NiTMTAA in the gas phase at two selected temperatures of 220 and 270 °C, which does not require the use of organic solvents and therefore can be considered as ecologically friendly. The nanohybrids obtained were characterized by means of scanning and transmission electron microscopy, energy dispersive X-ray, Fourier-transform infrared and Raman spectroscopy, as well as thermogravimetric analysis. An additional insight into the structure of adsorption complexes of NiTMTAA on CNTs was provided from density functional theory and molecular mechanics calculations.

A new family of belt-shaped carbon structures, called Escherynes, is theoretically proposed using the octadehydro annulene (ODA) skeleton as a building block. Several ODA rings are fused together and cyclized to form belt-structures. Two isomeric forms of the Escherynes are considered, Huckel and Mobius. We demonstrate that these compounds have thermodynamical and kinetic stabilities comparable to fullerenes. Density functional calculations of the structures revealed: (i) that Escherynes are relatively stable molecules, (ii) they have high affinity for lithium, (iii) large Mobius Escherynes (>60 atoms) are as stable as Huckel belts, and (iv) Mobius Escherynes display remarkable optical activity.

[18]-Annulene has been of great interest from the structural point of view of its bond alternation. High-level calculations based on structures selected for agreement with NMR spectra lead to a bond-alternate C 2 form over a non-alternating planar D 6h structure deduced from diffraction, infrared (IR) and electronic spectral studies. Here it is shown that computed Raman spectra for the D 6h and C 2 forms are expected to be very different. However, two equivalent non-D 6h bond-alternate minima of D 3h or C 2 geometries are separated by only a small barrier along a motion that involves CC stretching and compression. It is shown here that the zero-point level is above the barrier for this species. In light of that fact, the NMR calculations are reconsidered with inclusion of zero-point level averaging.

A homologous series of five tetrasubstituted dibenzotetraaza[14]annulene-based discotic mesogens was prepared and studied using polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). A nematic phase was identified for the product bearing two peripheral isobutoxy and two dodecyloxy substituents.

Huckel–London–Pople–McWeeny (HLPM) ‘topological’ ring-currents calculated for certain [ N ]-circulenes are in accord with (a) the previous generalised predictions based on the London approach and (b) the ab-initio ipso-centric π-electron current-density maps that this series of conjugated structures does not conform to the ‘annulene-within-an-annulene’ (AWA) model. These considerations are extended beyond the [ N ]-circulenes to a series of structures formally related to kekulene. One such system studied, anti-kekulene, with a [4 n ]-perimeter ( n = 6) and [4 n ]-central ring ( n = 3), exhibits paramagnetic topological bond-currents in its periphery, and a mixture of both paramagnetic and diamagnetic bond-currents in its central (overall, paramagnetic) ring.

3,10-Dipyrrolidinyl-4,9-methanothia[11]annulene reacts with excess dimethyl acetylenedicarboxylate (DMAD) in refluxing toluene to give ring-enlarged 6,11-methanothia[15]annulene. X-ray crystallographic analysis of the product shows two different cis,trans-dienyl parts in the ring system. Product formation possibly involves π-facial selective addition of the enamine with DMAD and torque-selective ring opening of the intermediate cyclobutenes.

The structures and magnetic properties of the parent cyclazines [2.2.2], [3.2.2], [3.3.2], [4.2.2], [3.3.3], [4.3.2], their topological isomers and the doubly bridged [14] to [18] annulenes were studied computationally at the B3LYP/6-311+G ** level of density functional theory (DFT). The magnetic criteria Λ (magnetic susceptibility exaltations, MSE), ∑NICS (the summation of nucleus-independent chemical shifts), and 1 H NMR chemical shifts, geometry-based HOMA (harmonic oscillator model of aromaticity) index and HOMO–LUMO gaps were used to elucidate their aromatic and anti-aromatic properties. The excellent correlation between Λ and the summation of NICS(0) and NICS(1) demonstrates that these two originally proposed indices are still good indicators of the whole aromaticity of these polycyclic ring systems. The computed NMR chemical shifts are also in good agreement with available experimental data. In general, there is a good relationship between different criteria of aromaticity.

New 7,15-dibromo-, 7,15-di(bromomethyl)-, and 7,15-di[4-(bromomethyl)phenyl]-1,5,9,13-tetraaza[16]annulene derivatives are synthesized via the condensation reaction of 2-substituted vinamidinium salts [2-substituted 3-(dimethylamino)- N , N -dimethyl-2-propen-1-aminium salts] with 1,8-diaminonaphthalene in acetonitrile/acetic acid. The ultraviolet spectral behavior of these compounds is examined in DMSO.

Geometry and vibrational structure of dibenzo[b,i][1,4,8,11]tetraaza[14]annulene (TAA) have been studied using infrared and Raman spectroscopy combined with quantum-chemical calculations. The assignments were proposed for 106 out of the total of 108 TAA vibrations, based on comparison of the theoretical predictions with the experimental data obtained for the parent molecule and its isotopomer in which the NH protons were replaced by deuterons. Reassignments were suggesteded for the NH stretching and out-of-plane vibrations. The values of the parameters of the intramolecular NH⋯N hydrogen bonds were analysed in comparison with the corresponding data for porphyrin and porphycene, molecules with the same structural motif, a cavity composed of four nitrogen atoms and two inner protons. Both experiment and calculations suggest that the molecule of TAA is not planar and is present in a trans tautomeric form, with the protons located on the opposite nitrogen atoms.

Four new water-soluble derivatives of dibenzotetraaza[14]annulene have been synthesized, bearing meso substituents with different structures and dimensions: 3-(N,N,N-trimethylammonium)propyl, 3-(N-pyridinium-1-yl)propyl, 2-[3-(N,N,N-trimethylammonium)propoxy]benzoyl, and 2-[3-(N-pyridinium-1-yl)propoxy]benzoyl. The crystal structures of 3-(trimethylammonium)propyl and (N,N,N-trimethylammonium)propoxy]benzoyl derivatives were determined by single crystal X-ray analysis. According to the UV–vis titrations, thermal denaturation experiments, and ethidium bromide displacement assays, all compounds presented here interact strongly with double stranded (ct)-DNA. The product equipped with 3-(trimethylammonium)propyl pendant groups and two positive charges interacts with DNA in one dominant binding mode, whereas the other three derivatives revealed more complex mixed-type interactions. The results have been discussed in terms of dimensions, geometry, and electronic properties of the evaluated compounds, on the basis of corresponding crystallographic data.

A new efficient protocol for the synthesis of benzannulated pyrido[2,3-d]- and pyrido[3,2-d]pyrimidines has been successfully accomplished via the palladium-catalyzed intramolecular arylation of C–H bond of pyrimidine moiety. The methodology has also been extended to the synthesis of pyrimido[5,4,-c]isoquinoline-2,4,6(1H,3H,5H)-trione derivatives in excellent yields.

Addition of silyl and germylmethyl azides ( 1 ) to fullerene C 60 at 50 °C through [2+3] cycloaddition led to the formation of the triazoline adducts ( 2 ). Subsequently, heating 2 at 100 °C in the solid state, caused N 2 extrusion producing two different isomers, [5,6]-azafulleroid ( 3 ) and [6,6]-aziridinofullerene ( 4 ). The 13 C NMR spectrum of 3 had an absence of resonances in the aliphatic region for the fullerene C 60 cage, showing a fulleroid with C S symmetry. In contrast, 4 exhibited one sp 3 resonance in the aliphatic region for the fullerene C 60 cage, indicative of an aziridinofullerene with C 2V symmetry. However, MALDI-TOF mass characterization was hampered because ion peaks corresponding to the bis-adduct are detected in positive ion mode measurements, whereas the ion peaks [M−N 2 ] − for 2a as well as [M] − for 3a and 4a are observed in negative ion measurements. In an effort to obtain X-ray data, silyl and germylphenyl groups were introduced to form intermolecular complexes with fullerene C 60 . The X-ray structures of 3c and 3d revealed a strong enhancement of homoconjugation in the bridged annulene moiety based on POAV analysis. The X-ray structures of 3c , d and 4c were confirmed with the detection of silyl and germylphenyl-C 60 interactions, similar to dimethoxyphenyl-C 60 interactions.

A short series of dehydrobenzothieno- and dehydropyridothieno[15]annulene ([15]DBTA and [15]DPTA) hybrids were assembled from thiophene, acetylene, and benzene/pyridine components. The molecules were constructed in a convergent manner and their properties examined optically, electrochemically, and thermally. In addition to lowered energy of electronic transitions of the 15-membered macrocycles, their emissive properties are discussed. The observed trends correspond with previously reported [14]annulenes, and are further rationalized using DFT (B3LYP/6-311G ∗∗ ) calculations.

This computational organic chemistry study presents results based on density functional theory at the B3LYP/6-31G(d) and B3LYP/cc-PVTZ//B3LYP/6-31G(d) levels of theory. Other computational procedures (HF and MP2) are presented for model structures. Three main points were investigated: some of the electronic structure aspects, the relative stability of isomers, and aromaticity. The results suggest that the title salts are the first Schiff base systems in the literature to exist only in the N–H form, which is characterized as the zwitterion form. Also, the estimated delocalization of the π-electron density in the middle ring indicates that these compounds are the first examples of metalla-hetero[10]annulenes. Analysis of the electron density delocalization indicates that the title compounds are better conductors at the molecular level than the parent Schiff base, and therefore, can be considered as new building blocks for organic materials.

Ab initio plane wave based all valence electron DFT calculations with geometry optimization are reported for the electronic structure of planar zigzag edged triangular shaped graphene molecules C m ∗ ∗ 2 + 4 m + 1 H 3 m + 3 where the zigzag ring number m = 2, …, 15. The largest molecule C 286 H 48 has a 3.8 nm side length and retains D 3 h symmetric geometry. The zone in the middle of the molecules, where the geometry and electronic properties resemble infinite single sheet graphite (graphene), expands with increasing ring number m , driving deviations in geometry, charge and spin to the perimeter. If a molecule is viewed as a set of nested triangular rings of carbon, then the zone where the lattice resembles an infinite sheet of graphene with CC = 142 pm, extends to the middle of the penultimate ring. The radial bonds joining the perimeter carbon atoms to the interior are long CC = 144 pm, except near the three apexes where the bonds are shorter. Isometric surfaces of the total charge density show that the two bonds joined at the apex have the highest valence charge. The perimeter CC bonds establish a simple pattern as the zigzag number increases, which shares some features with the zigzag edges in the D 2 h linear acenes C 4 m +2 H 2 m +4 and the D 6 h hexangulenes C 6 m ∗ ∗ 2 H 6 m but not the D 6 h symmetric annulenes ( CH ) ( 2 m - 1 ) ∗ 6 . The two CC bonds forming each apex are short (≈139 pm), next comes one long bond CC ≈ 142 pm and a middle region where all the CC bonds have length ≈141 pm. The homo–lumo gap declines from 0.53 eV at m = 2 to approximately 0.29 V at m = 15, the latter being larger than found for linear or hexagonal shaped graphenes with comparable edge lengths. Across the molecule the charge on the carbon atoms undergoes a small oscillation following the bipartite lattice. The magnitude of the charge in the same nested triangle decreases monotonically with the distance of the row from the center of the molecule. These systems are predicted to have spin polarized ground states with S = ½( m − 1), in accord with the theorems of Lieb for a bipartite lattice with unequal numbers of sub-lattice carbon atoms. The magnitude of the spin on the atoms increases monotonically from the center to the edges, this effect being greatest on the majority A-sub lattice atoms. The spins are delocalized, not confined to specific atoms as might result in geometries stabilized by islands of aromatic resonance. In the largest systems the magnetic non-bonding levels (NBL) occur as a narrowly distributed set of homos close to the Fermi level, separated from the lower lying valence bond manifold by a gap of about 1 eV. The NBL are a set of disjoint radical orbitals having charge only on atoms belonging to the A-lattice and this charge is concentrated on the perimeter and penultimate row atoms.

Titration of three electron donor-functionalized bis(dehydrobenzo[n]annuleno)benzenes and a corresponding acyclic 1,2,4,5-tetrakis(phenylethynyl)benzene derivative with trifluoroacetic acid in CH2Cl2 resulted in two-stage emission switching behavior in which initial acidification caused bathochromic shifts, followed by dramatic hypsochromic shifts upon further addition of acid. Differences in the various spectra are rationalized by structure and chromophore architecture. The results indicate independent manipulation of frontier molecular orbital energy levels by stepwise ion addition, therefore suggesting transient and tunable intramolecular charge transfer systems upon partial protonation.

Dibenzo [1,4,8,11] tetraaza [14] annulene nickel (TAA-Ni) has been synthesized and its inhibitive behavior on mild steel in 1 M HCl was firstly investigated by gravimetric, potentiodynamic and impedance method. The potentiodynamic curves indicate the TAA-Ni mainly acted as mixed type inhibitor on electrochemistry in acid media. The weight loss result indicates TAA-Ni is good inhibitor in acid solution with the temperature changing from 303 K to 333 K. The XPS experiment indicates the protonation of TAA-Ni and its chemical adsorption on steel surface.

Three new lacunar-type derivatives of β-unsubstituted dibenzotetraaza[14]annulene have been synthesized along with a range of their open-chain pendant group containing counterparts. The crystal structures of two representative products have been determined and the noncovalent interactions explored. A number of C–H⋯π and π⋯π interactions involving aliphatic chains and aromatic regions of the macrocycle have been evidenced. The relative ease and high yield of lacunization are suggested to be largely due to self-assembly processes, driven by favorable noncovalent interactions between reacting units.

Electronic absorption and florescence spectra of dehydro[18]annulene and dehydrobenzo[18]annulene have been predicted with the singlet-excitation configuration interaction method. Four electronic absorption bands observed in the experiments have been assigned to electronic transitions. With the application of the Kasha’s rule, three florescence peaks of dehydrobenzo[18]annulene observed in experiment have been assigned to electronic transitions of different distortional excited states. The Jahn–Teller effect leads to the excited-state distortions, and the distortional excited state with the large oscillator strength is responsible for the strong multiple florescences.

DFT calculations for M@C 12 H 12 N 6 and M@C 12 H 24 O 6 (where M = Rb + , Cs + , Sr 2+ , and Ba 2+ , C 12 H 12 N 6 = hexaaza[18]annulene, and C 12 H 24 O 6 = 18-crown-6) were performed using the recently developed model core potential parametrization. Results show that the ions bind more strongly to C 12 H 12 N 6 than to 18-crown-6 moiety; the difference is more pronounced for cations with smaller radii.

The tropone-fused 1,6-methano[10]annulene 4 was synthesized from 3,4-bis(bromomethyl)-1,6-methano[10]annulene and the protonation of 4 provided the hydroxytropylium ion-fused annulene 5 . 1 H NMR spectra of 4 and 5 exhibited an unequal shielding effect on the bridge hydrogens from the resulted π ring system, suggesting the existence of the significant homoconjugative transannular interaction on the nonadjacent carbons at the bridge and the discreteness of π-conjugation of the annulene between two bonds at the C7–C8 and C11–C12 to localize the C8–11 dienyl and the remaining parts. The X-ray crystallographic structures of 4 and 5 show relatively short atomic distance between those bridge carbons, and clear bond alternation of the dienyl part and the bond convergence of the remaining part in these compounds, supporting the spectral properties.

The absorption spectra. cyclic voltammetry and spectroelectrochemistry of [Ni(II)DPTAA] and [Co(II)DPTAA] (DPTAA = 6,13-diphenyldibenzo[b,i][1,4,8,11] tetraaza[14]annulene) complexes in DMF are reported in detail. The ligand oxidation is observed for [Ni(II)DPTAA] at +0.70 V vs. SCE whereas Ni2(+/+) occurs at - 1.60 V. For [Co(II)DPTAA], a ligand oxidation redox couple is seen at +0.56 V while the Co2+/+ and Co2+/3+ redox couples appear at -1.21 and +0.24 V, respectively. All observed redox couples are assigned to reversible one-electron processes on account of peak separations and scan-rate dependency. These processes were further investigated by spectroelectrochemistry for [Co(II)DPTAA]. For [Co(II)DPTAA], axial ligation of pyridine was found to shift the Co2+/3+ redox couple more negative. while the ligand oxidation was shifted to more positive potentials. From a spectrophotometric titration of [Co(II)DPTAA] with pyridine an equilibrium constant, K-f, was determined for the binding of pyridine to [Co(II)DPTAA]. This was found to be 10.2 dm(3) mol(-1), slightly lower than that of [Co(II)TAA], indicating the influence of the phenyl groups. From this value and shifts in the Co2+/3+ redox couple upon ligation, an equilibrium constant for the binding of pyridine to [Co(III)DPTAA], K'(f), was found to be 5.06 x 10(6) dm(3) mol(-1). (c) 2007 Elsevier B.V. All rights reserved.

In this paper, we review the electronic aromaticity measures from the perspective of the Huckel molecular orbital (HMO) theory. The analysis of FLU, PDI, I ring and SCI in the framework of the HMO theory provides an interesting scenario for the interpretation of these indices. Within the Huckel theory the formulas for the Coulson bond orders are easily obtained in a closed form for annulenes, which enables the production of analytical expressions for some of the aromaticity measures. These analytical functions are used to study the ring size dependence of current aromaticity indices. Besides, HMO calculations of polycyclic benzenoids complete the analysis of the electronic aromaticity indices reviewed in this paper, by showing how HMO theory explains the changes in aromaticity due to annulation. All these results help grasping the meaning and the behavior of the electronic aromaticity indices.

Through space NMR shieldings of aromatic (benzene, mono-substituted and annelated benzenes, ferrocene, [14]- and [18]-annulenes, phenylenes and tetra- to heptahelicene) and anti-aromatic molecules (cyclobutadiene and pentalene) were assessed by ab initio molecular-orbital calculations. Employing the nucleus-independent chemical shifts (NICS) concept, these through space NMR shieldings were visualized as iso-chemical-shielding surfaces (ICSSs) and can be applied quantitatively to determine the stereochemistry of proximal nuclei. In addition, the distances in Å at ICSS values of ±0.1 ppm in-plane and perpendicular-to-center of the aromatic ring system were employed as a simple means to compare and estimate qualitatively the aromaticity of the systems at hand.

Syntheses of all-Z-tribenzo[12]annulenes (1a–c) and Z,Z-tribenzodidehydro[12]annulenes (2a–c) by the reduction of the corresponding tribenzohexadehydro[12]annulenes 3a–c were carried out using a low valent titanium complex generated from Ti(O-i-Pr)4 and i-PrMgCl. The unique structure of the first reduction products 2a–c as well as 1a–c was fully characterized. Complexation of these annulenes with silver(I) ions produces the corresponding silver complexes. Among them, the silver complexes of 2a–c exhibit interesting monomer–dimer equilibrium.

On the basis of the equilibrium geometric structures obtained at the B3LYP/6-31G level, the one-photon absorption (OPA) and two-photon absorption (TPA) properties of donor/acceptor-functionalized tetrakis(phenylethynyl)benzenes (TPEBs) and bis(dehydroben-zoannuleno) benzenes (bisDBAs) have been determined by using ZINDO-SOS method. The influence of the molecular structures on OPAs and TPAs have been discussed. Among the donor/acceptor substituted regioisomers, the ortho- and meta-substituted compounds have the largest two-photon responses, mainly due to the existence of the larger dipole moment differences between the ground states and the intermediate states. The diacetylene bridges in bisDBAs result in the red-shift of OPAs and TPAs and decrease of TPA cross-sections. From the point of view of transparency/nonlinearity, the TPEBs and bisDBAs are promising candidates for TPA materials.

A new dibenzotetraaza[14]annulene ligand has been synthesized that contains two 2-hydroxybenzoyl and four 3,7-dimethyloctyloxy peripheral substituents. Its mesomorphic textures were observed by means of a polarizing optical microscopy.