Conjugation Circuit Research Articles

Computational Analysis of Some More Rectangular Tessellations of Kekulenes and Their Molecular Characterizations.

Cycloarene molecules are benzene-ring-based polycyclic aromatic hydrocarbons that have been fused in a circular manner and are surrounded by carbon-hydrogen bonds that point inward. Due to their magnetic, geometric, and electronic characteristics and superaromaticity, these polycyclic aromatics have received attention in a number of studies. The kekulene molecule is a cyclically organized benzene ring in the shape of a doughnut and is the very first example of such a conjugated macrocyclic compound. Due to its structural characteristics and molecular characterizations, it serves as a great model for theoretical research involving the investigation of π electron conjugation circuits. Therefore, in order to unravel their novel electrical and molecular characteristics and foresee potential applications, the characterization of such components is crucial. In our current research, we describe two unique series of enormous polycyclic molecules made from the extensively studied base kekulene molecule, utilizing the essential graph-theoretical tools to identify their structural characterization via topological quantities. Rectangular kekulene Type-I and rectangular kekulene Type-II structures were obtained from base kekulene molecules arranged in a rectangular fashion. We also employ two subcases for each Type and, for all of these, we derived ten topological indices. We can investigate the physiochemical characteristics of rectangular kekulenes using these topological indices.

Quest for the Most Aromatic Pathway in Charged Expanded Porphyrins.

Despite the central role of aromaticity in the chemistry of expanded porphyrins, the evaluation of aromaticity remains difficult for these extended macrocycles. The presence of multiple conjugation pathways and different planar and nonplanar π-conjugation topologies makes the quantification of global and local aromaticity even more challenging. In neutral expanded porphyrins, the predominance of the aromatic conjugation pathway passing through the imine-type nitrogens and circumventing the amino NH groups is established. However, for charged macrocycles, the question about the main conjugation circuit remains open. Accordingly, different conjugation pathways in a set of neutral, anionic, and cationic expanded porphyrins were investigated by means of several aromaticity indices rooted in the structural, magnetic, and electronic criteria. Overall, our results reveal the predominance of the conjugation pathway that passes through all nitrogen atoms to describe the aromaticity of deprotonated expanded porphyrins, while the outer pathway through the perimeter carbon atoms becomes the most aromatic in protonated macrocycles. In nonplanar and charged macrocycles, a discrepancy between electronic and magnetic descriptors is observed. Nevertheless, our work demonstrates AVmin remains the best tool to determine the main conjugation pathway of expanded porphyrins.

A Study on Automatically Target-Chasing Microwave Power Transfer Systems in Multipath Environments

In this paper, we propose novel retrodirective systems to improve the efficiency and safety of microwave power transmission (MPT) systems in multipath environments. The retrodirective system consists of an array antenna with phased conjugation circuits and it sends back the phase-conjugate signal toward the pilot signal transmitted from the receiver. It is usually applied for one receiver MPT system, however, Ossia corp. develops the new retrodirective system in multipath environments named ‘Cota’. We simulated the detail of the Cota system, e.g., one receiver in multipath circumstance, one receiver with obstacle in the multipath circumstance, and multi receiver. Furthermore, we revised the retrodirective system with phase information as well as the amplitude information of the pilot signal to improve the MPT efficiency. We also find effect of the MPT efficiency by phase difference between two pilot signal sources. At last, we carried out the experiments of the retrodirective system in multipath circumstance to prove the simulation results.

Inside Cover: Dianion and Dication of Tetracyclopentatetraphenylene as Decoupled Annulene‐within‐an‐Annulene Models (Angew. Chem. Int. Ed. 6/2022)

Dianion and dication 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. 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).

Dianion and Dication of Tetracyclopentatetraphenylene as Decoupled Annulene‐within‐an‐Annulene Models

AbstractThe 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.

Dianion and Dication of Tetracyclopentatetraphenylene as Decoupled Annulene-within-an-Annulene Models.

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 13 C 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.

Topological characterization of hexagonal and rectangular tessellations of kekulenes as traps for toxic heavy metal ions

Cycloarenes are polycyclic aromatic hydrocarbons formed by circularly fused benzene rings, which provide a potential cavity trap for metal ions. These polycyclic aromatics have been the focus of several studies due to their superaromaticity, magnetic and other electronic and geometric properties. The first representative of these macrocyclic conjugated compounds is kekulene, a doughnut-shaped structure consisting of cyclically arranged benzene rings with intriguing structural features that are suitable for theoretical studies including the study of conjugation circuits of $$\pi $$ electrons. Topological characterization of such structures is thus essential for the prediction of their properties. In this study, we present two novel series of giant polycyclic compounds that are generated through tessellations of several kekulene doughnuts providing a potential molecular belt with multiple cavities. We have computed a number of topological quantity indices for such a 2D-sheet comprising of several kekulenes.

Stable meso-Aryl β-Alkyl Hybrid Sapphyrin with a Warped π-Conjugation Circuit and Neo-Confused Sapphyrin-Silver(I) Complex.

A meso-aryl and β-alkyl substituted sapphyrin and its rhodium(I) and silver complexes were synthesized. This sapphyrin was so stable that the non-inverted and warped structure could be analyzed by X-ray crystallography even in its neutral state. Its bis-rhodium(I) complex has a more planar structure than the sapphyrin with enhanced aromaticity over the conjugation circuit. On the other hand, silver metalation of the sapphyrin caused a marked core rearrangement into a neo-confused sapphyrin derivative with a C(α)-N bond and a twisted macrocycle.

Non-alternant non-benzenoid kekulenes: the birth of a new kekulene family.

"Kekulene" is a doughnut-like shaped polycyclic aromatic hydrocarbon consisting of cyclically arrayed benzene rings. It has attracted a great deal of theoretical interest because it is regarded as an ideal model to study conjugation circuits of π electrons, i.e. whether they delocalize locally in benzene rings or globally throughout the molecule. Though kekulene was synthesized in 1978, it was the only known compound of this class of compounds for a long time. Recently, new kekulene-related molecules, septulene, which is a non-alternant benzenoid hydrocarbon, and a tetracyclopentatetraphenylene (TCPTP) derivative belonging to non-alternant non-benzenoid hydrocarbons, were synthesized. This article presents theoretical and experimental aspects of kekulene-related molecules focusing on the viewpoint of conjugation circuits by classifying them into three types: benzenoid kekulenes including kekulene itself and septulene, yet unknown anti-kekulene and non-alternant non-benzenoid kekulenes represented by TCPTP.

Analytical Study of Superaromaticity in Cycloarenes and Related Coronoid Hydrocarbons

Recently synthesized septulene is a unique cycloarene molecule in that no macrocyclic conjugation circuits can be chosen from the π-system. This molecule has essentially no superaromatic stabilization energy (SSE) and can be viewed as an ideal nonsuperaromatic macrocycle. SSEs for kekulene and other cycloarenes are also very small. In these hydrocarbons, a macrocycle formed by fused benzene rings effectively suppresses not only the aromaticity inherent in macrocyclic (4n+2)-site conjugation circuits but also the antiaromaticity inherent in macrocyclic (4n±1)-site circuits. Comparative study of superaromaticity in multilayered coronoid hydrocarbons revealed that not only SSE but also the HOMO contribution to SSE is minimized in odd-layered coronoids.

Critical role of weak [C–H⋯O] hydrogen bonds in the assembly of benzo[1,2-d:4,5-d′]bisoxazole cruciforms into supramolecular sheets

This paper explores the structural patterns adopted by a class of eight conjugated cruciforms based on a benzo[1,2-d:4,5-d′]bisoxazole (BBO) nucleus. Within the series, the lengths of cruciforms' x- and y-axes, as well as their terminal substituents, were varied. Two new cruciforms have been prepared using microwave-assisted Sonogashira couplings. Examination of molecular structures of BBO cruciforms revealed the expected cross-shaped geometries, with ∼90° crossing angles between the two conjugation circuits. Most significant deviations from the idealized planar structures were caused by the distortion of benzene rings positioned along the cruciforms' y-axis from the plane of the central benzobisoxazole ring, by as much as 82.1°. Deviations from linearity within carbon–carbon triple bonds were mild, but additively resulted in notably bent y-axes of the two largest examined cruciforms. Most significantly, the packing patterns of benzobisoxazole cruciforms revealed three distinct organizational motifs. Cruciforms with carbonyl groups on either the horizontal or the vertical axis (or both) all organized into two-dimensional infinite sheets, apparently connected chiefly through [C–H⋯O] contacts that varied in length between 2.24 and 2.60 A, and could be interpreted as weak hydrogen bonds. The parallel layers of these two-dimensional sheets then assembled into three-dimensional structures through [π⋯π] stacking between the layers. The packing patterns of the two cruciforms with 4-(N,N-dimethylamino)phenyl groups on the vertical axis are dominated by one-dimensional columnar or tape-like assemblies that are formed through [π⋯π] stacking; these then organize into two-dimensional sheets, which in turn layer into a three-dimensional structure, but with a ∼60° angle between the adjacent sheets. Finally, in the parent tetraphenyl-substituted cruciform, the sp2 nitrogen on the BBO core plays the key role in the assembly. It establishes 2.64 A-long [C–H⋯N] contacts with the phenyl groups, mediating the formation of a unique packing pattern in which six tilted columnar assemblies of [π⋯π] stacked cruciforms surround a three-fold rotation axis in the crystal.

Design of an Active Phase Conjugation Circuit for Retrodirective Array in UHF Band

An active phase conjugation circuit of retrodirective array which can be used in UHF band (890-960MHz) has been designed. Circuit of the retrodirective array consists of filters, mixers, dividers and other microwave devices. In this paper, microstrip filters and mixers are primarily designed. Divided matching circuit will be designed appropriate on the basis of the antenna element. Filters consist of microstrip coupled lines to conform with microstrip antenna arrays; to suppress the effect of RF input signals to output transmitted signals, selecting the image-rejection mixers. Simulation results of ADS show that all of the designed active devices display good performances.

Enumeration of conjugated circuits in nanotubes.

The resonance energy of (1,1)n "armchair" carbon nanotubes and (n,n)1 nanoribbons was determined by enumerating the conjugated circuits (CC) and the Kekulé structures. The lower indices denote the number of hexagon layers. It was found that the resonance energy per carbon atom is equal to 0.160 eV in (1,1)n tubes and 0.142 eV in (n,n)1 tubes.

A Retro-Directive Antenna Array With Phase Conjugation Circuit Using Subharmonically Injection-Locked Self-Oscillating Mixers

In this paper, a novel phase conjugation circuit and its application to retro-directive antennas are presented. The phase conjugation circuit uses a balanced circuit structure with subharmonically injection locked self-oscillating mixers oscillating at /spl omega/. In the operation, an input signal at /spl omega//2 is converted to its conjugated signal with no external source required for LO signal pumping, and the output signal frequency is locked at the same frequency of the input signal. The developed phase conjugation circuit is implemented with active antennas to become a retro-directive antenna array. Both the theoretical and measured results of phase conjugation and retro-directive performance are shown in good agreement.

Efficient method for calculating the resonance energy expression of benzenoid hydrocarbons based on the eunumeration of conjugated circuits

To reduce the calculating time for the summations over linearly independent and minimal conjugated circuits of benzenoid hydrocarbons (BHs), an approximate method is proposed that counts only the numbers of the first four classes of conjugated circuits R1, R2, R3, and R4, respectively. By representation of BHs as custom-made "ring-block chains" and use of the techniques of Database and visual computing, an application software is realized that is much faster and more powerful than the old one based on an enumeration technique.

Triscyclopenta[cd,fg,jk]pyrene: another congener of the externally cyclopenta-fused pyrene series

Flash vacuum thermolysis of 1,3,6-tris(1-chloroethenyl)pyrene 5 between 900–950 °C gave the thermally labile triscyclopenta[cd,fg,jk]pyrene 1; in line with the ‘conjugated circuits model’ and supported by IGLO III//RHF/6-31G calculations, all hydrogen atoms of 1 are additionally shielded by 0.4–0.9 ppm (1H NMR).

Analytical expressions for the count of LM-conjugated circuits of benzenoid hydrocarbons

A recursive method for enumeration of linearly independent and minimal conjugated circuits of benzenoid hydrocarbons had previously been given which is valid for several classes of benzenoid hydrocarbons. In the present article, the properties and constructions of unique minimal conjugated circuits and pairs of minimal conjugated circuits of a ring s in a benzenoid hydrocarbon B are investigated. An analytical expression for the count of LM-conjugated circuits of B is given which is based on the counts of Kekulé structures of selected subgraphs of B. By using the method, the LMC expression of any benzenoid hydrocarbon can be obtained. © 1996 John Wiley & Sons, Inc.

Stability of fullerenes with four-membered rings

Fullerenes with four-membered rings with up to 60 atoms were systematically generated and their stability examined by the conjugated circuits (CC) model and the topological resonance energy (TRE) model. As none of the models accounts for strain, which is important in spherically shaped conjugated systems with four-membered rings, the results are only qualitative. Values of resonance energy obtained by the two models show remarkable disagreement. Isomers selected as the most stable are quite different in dependence on the criterion used. The structures selected by TRE possess a small number or no four-membered rings (for C 60, buckminsterfullerene was selected), while those selected by the CC model sometimes possess greater numbers (up to 6) of four-membered rings, paired by a common edge.

Generalized bond orders

AbstractWe introduce generalized bond orders defined in terms of weighted Kekule valence structures. The weights were determined by the contributions of linearly independent and minimal conjugated circuits in individual Kekule valence structure. When special values for the contributions of conjugated circuits of different size are assumed, one obtains quantities that show considerable similarity to the Pauling and the Clar's bond orders. Pauling bond orders are obtained when one assumes that all conjugated circuits make equal contribution to bond orders. © 1994 John Wiley & Sons, Inc.

Photoinduced NH-tautomerism and vibronic states of hydroporphyrin molecules

Hydroporphyrin microcycles are the chromophores of the most important biologically active pigments, among which we should primarily name chlorophyll, which is a universal photosynthetic pigment. Their biological function must have a close connection with the electronic structure of the molecules, and therefore investigations into the spectroscopic properties of the molecules of hydroporphyrins were conducted in many laboratories. For a number of years, to study such molecules we have applied the Shpol'skii method of quasi-bright-line spectra and other methods of fine-structure spectroscopy [1, 2]. In the present paper we sum up the available data on electronic and vibrational states of hydroporphyrin molecules. First, we shall consider the problem of the structure of hydroporphyrin molecules and of their photoinduced NHrestructurization, in the molecule of nonsubstituted dihydroporphin (DHP) or chlorin, just as of any chlorin substituted at the periphery, the central imino-hydrogens can be located on the axis perpendicular to the symmetry axis C 2, as shown in Fig. 1, on the axis C 2 (in the both cases, an exact or approximate symmetry of the conjugate system C2v), and also in various combinations, i.e., near the neighboring nitrogen atoms (see Fig. 1). It is thought that in the ground state the first structure is realized (we shall designate it as structure A). This structure involves a closed 18-term cycle of alternating simple and double bonds and therefore it can be called "classical." The second structure (B) corresponds to formal rupture of the conjugation circuit in a microcycle (it is completed through the imine nitrogen atom) and can be called "nonclassical." Structures with neighboring arrangement of imino-hydrogens will be called structures of type C. They can be both "classical" and "nonclassical." In a DHP molecule and other symmetric chlorins, only two such structures are possible, i.e., one "classical" and one "nonclassical" (C and C' in Fig. 1). Reference [3] quotes unpublished quantum-chemical data (of the same authors) on the ground state energy calculated for hydroporphyrins by the CNDO/2 method. According to these data, the energy of structure B for DHP is higher by about 0.8 eV than the energy of structure A. This explains the above-noted experimental fact of the existence of chlorins precisely in form A. By analogy with porphyrins, it is natural to expect that structures of type C will also have a higher energy than those of type A, chiefly because of the van der Waals repulsion of imino-hydrogens. Hydrogenation of the second pyrrole ring in the porphyrin macrocycle is possible in two versions: either the opposite pyrrole ring is hydrogenated or the neighboring one. In the first case, there originates the structure of tetrahydroporphyrin of "opposite" type (OTHP), or bacteriochlorine (BC), in the second case, of "neighboring" type (NTHP), or isobacteriochlorine (IBC). The data of [3] show that in the OTHP case the energy of the "nonclassical" structure B exceeds that of structure A by about 1.9 eV. It can be claimed that here too structure A is realized. It should be noted that the OTHP structure for the simplest BC (an analog of bacteriochlorophyll) has been rigorously proved by the method of quasi-line spectra (QLS) [4] by the presence of the symmetry center in a molecule. In the case of NTHP and its derivatives, there are a number of experimental data (see references in [5]) testifying to the fact that predominantly A and B structures are realized (equivalent in symmetric substitution) which now are "nonclassical." The 'classical" structure C is present in the form of an accompanying tantomer. However, the introduction of an electronic acceptor cyanogroup into meso-position 5 results in the stabilization of "classical" structure C [6]. The A, B or C-type NH-isomers, which do not exist at room temperature (or have a small relative concentration), can form at low temperatures as a result of the photoinduced translation of NH protons. This phenomenon was discovered for porphyrins in [7, 8]. For hydroporphyrins it was observed for the first time in [9, 10].