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Cyclobuta[1,2-b:3,4-b′]ditetracene – an analogue of nonacene with a cyclobutadiene unit embedded in the central part has been synthesized by the combination of solution and on-surface chemistry.

This review surveys recent progress in the chemistry of polycyclic heteroaromatic molecules with a focus on structural diversity and synthetic methodology. The article covers literature published during the period of 2016–2020, providing an update to our first review of this topic (Chem. Rev.2017, 117 (4), 3479–3716).

Tridecacyclene tetraimide, TCTI, an electron-deficient non-benzenoid nanocarbon with a C

Unsymmetrically fused porphyrins containing one or two naphthalimide subunits were prepared in modular syntheses relying on electron-rich and electron-poor pyrrole building blocks. These new chromophores show progressive changes in their electron-deficient character, while retaining comparably small optical and electrochemical band gaps. The intrinsic curvature and extended optical absorption of these systems make them of interest as mono- and difunctional components of multichromophoric assemblies.

Free base, zinc and palladium π‐extended porphyrins containing fused naphthalenediamide units were employed as photosensitizers in antimicrobial photodynamic therapy (aPDT). Their efficacy, assessed by photophysical and in vitro photobiological studies on Gram‐positive bacteria, was found to depend on metal coordination, showing a dramatic enhancement of photosensitizing activity for the palladium complex., Photo finish it: Antimicrobial photodynamic therapy (aPDT) has been proposed as an alternative approach for the treatment of bacterial infections. Here, free base, zinc and palladium π‐extended porphyrins containing fused naphthalenediamide units were employed as photosensitizers in aPDT, assessed by photophysical and in vitro photobiological studies.

International audience; Boomerang-shaped bipyrroles containing donor-acceptor units were obtained through a tandem palladium-mediated reaction consisting of a cyclization step, involving double C-H bond activation, and a double alpha-oxygenation. The latter reaction can be partly suppressed for the least reactive systems, providing access to alpha-unsubstituted boomerangs for the first time. These "alpha-free" systems are highly efficient fluorophores, with emission quantum yields exceeding 80% in toluene. Preliminary measurements show that helicene-like boomerangs may be usable as circularly polarized luminescent materials.

Peripheral substitution of a π-extended porphyrin with bulky groups produces a curved chromophore with four helical stereogenic units. The curvature and stereochemistry of such porphyrins can be controlled by varying the substituents, coordinated metal ions, and apical ligands. In particular, when the achiral saddle-shaped free bases are treated with large metal ions, i.e., Cd

Circularly polarized luminescence (CPL) and Raman optical activity (ROA) were observed in a single spectroscopic experiment for a purely organic molecule, an event that had so far been limited to lanthanide-based complexes. The present observation was achieved for [16]cycloparaphenylene lemniscate, a double macrocycle constrained by a rigid 9,9′-bicarbazole subunit, which introduces a chirality source and allows the molecule to be resolved into two configurationally stable enantiomers. Distortion of oligophenylene loops in this lemniscular structure produces a large magnetic transition dipole moment while maintaining the π-conjugation-induced enhancement of the Raman signal, causing the appearance of the CPL/ROA couple. A two-photon mechanism is proposed to explain the population of the lowest-energy excited electronic state prior to the simultaneous emission-scattering event. We thank MINECO/FEDER of the Spanish Government (project reference PGC2018-098533-B-100 and PID2021-127127NB-I00) and the Junta de Andalucía, Spain (UMA18FEDERJA057). We also thank the vibrational spectroscopy unit of the Research Central Services (SCAI) of the University of Málaga. Financial support from the National Science Center of Poland (DEC-2015/19/B/ST5/00612, M.S.) is gratefully acknowledged. L.F. thanks Thomas Vives from the Ecole Nationale Supérieure de Chimie of Rennes, the Shimadzu and Chiral Technology companies for their support regarding the separation of the chiral molecule by supercritical fluid chromatography (SFC). Funding for open access charge: Universidad de Málaga/CBUA

π-Extended acenaphtho[1,2-d][1,2,3]triazoles, the unsubstituted Anta-H and its di-tert-butyl derivative Dibanta-H, as well as 5,6,7,8-tetrahydro-1H-naphtho[2,3-d][1,2,3]triazole Cybta-H were obtained in concise syntheses. In the solid state, Dibanta-H forms an unprecedented hydrogen-bonded cyclic tetrad, stabilized by dispersion interactions of the bulky tBu substituents, whereas a cyclic triad was found in the crystal structure of Anta-H. These cyclic assemblies form infinite slipped stacks in the crystals. Evidence for analogous hydrogen-bonded self-assembly in solution was provided by low-temperature NMR spectroscopy and computational analyses. Kuratowski-type pentanuclear complexes [Zn5 Cl4 (Dibanta)6 ] and [Zn5 Cl4 (Cybta)6 ] were prepared from the respective triazoles. In the Dibanta complexes, the π-aromatic surfaces of the ligands extend from the edges of the tetrahedral Zn5 core, yielding an enlarged structure with significant internal molecular free volume and red-shifted fluorescence.

A hybrid nanocarbon receptor consisting of a calix[4]arene and a bent oligophenylene loop ("molecular squid"), was obtained in an efficient, scalable synthesis. The system contains an electron-rich cavity with an adaptable shape, which can serve as a host for electron deficient guests, such as diquat, 10-methylacridinium, and anthraquinone. The new receptor forms inclusion complexes in the solid state and in solution, showing a dependence of the observed binding strength on the shape of the guest species and its charge. The interaction with the methylacridinium cation in solution was interpreted in terms of a 2:1 binding model, with K11 = 5.92(7) × 103 M-1. The solid receptor is porous to gases and vapors, yielding an uptake of ca. 4 mmol/g for methanol at 293 K. In solution, the receptor shows cyan fluorescence (λmaxem = 485 nm, ΦF = 33%), which is partly quenched upon binding of guests. Methylacridinium and anthraquinone adducts show red-shifted emission in the solid state, attributable to the charge-transfer character of these inclusion complexes.

A diindenophenanthrene biradicaloid, formally derived from Chichibabin's hydrocarbon, is obtained in a short, scalable synthesis. The present system is electron-rich and devoid of conjugated substituents, and still exhibits very good stability under ambient conditions. The introduction of the diindeno[1,2-a:2′,1′-i] phenanthrene ring framework results in a singlet biradicaloid system with an easily accessible triplet state (ΔES–T = −1.30 kcal mol−1) and a small electronic bandgap (1.39 V). The stability limits of the title hydrocarbon were explored systematically in the solid state, to reveal an unusual thermally initiated hydrogen-scrambling oligomerization process.

Cel – Celem opracowania jest identyfikacja i opis zalezności ujawnien w zakresie dokumentacji cen transferowych a sprawozdawczością finansową podmiotow gospodarczych. Metodologia badania – W artykule zawarto monograficzną metodologie badania, wykorzystując infor-macje w formie jakościowo - opisowej. Poddano metodzie analizy i konstrukcji logicznej piśmiennictwo istniejące w zakresie badanego zagadnienia, uwzgledniając istniejący zakres prawa podatkowego. Wynik – Wynikiem badan jest kwantyfikacja roznic i podobienstw w zakresie ujawnien aktywow, funkcji, ryzyk i realizowanych przez podmiot strategii w obszarze prawa podatkowego i bilansowego. Oryginalnośc/Wartośc – Jednym z elementow szeroko rozumianego otoczenia ekonomicznego, jest sys-tem rachunkowości dostarczający odbiorcom informacji o wynikach jednostki i sytuacji majątkowo-finansowej. Do szeroko rozumianego otoczenia ekonomicznego zaliczamy rowniez otoczenie fiskalne. Prawo podatkowe, sluząc glownie celom fiskalnym panstwa, realizuje jedną z podstawowych funkcji systemu podatkowego, do ktorych nalezy funkcja fiskalna. Prawo bilansowe sluzy glowne do informowania wlaścicieli kapitalow jednostki o szeroko rozumianych wynikach finansowych uzyskiwanych przez jednostki gospodarcze. Zmiany w zakresie ujawnien danych ekonomicznych w zidentyfikowanych dwoch systemach, stanowią istotny element zarządzania generowanymi przez podmiot informacjami zarowno w zakresie podatkow jak i sprawozdawczości finansowej.

A 139-π-electron nanographenoid radical was obtained by expanding the periphery of a naphthalimide–azacoronene hybrid with a methine bridge. The radical was isolated in the form of its σ-dimer, which was shown to possess a conformationally restricted two-layer structure both in the solid state and in solution. The dimer is cleaved into its parent radicals when exposed to ultraviolet or visible radiation in toluene solutions but is resistant to thermally induced dissociation. Under inert conditions, the radicals recombine quantitatively into the σ-dimer with observable kinetics, but they are oxidized into a ketone derivative in the presence of atmospheric oxygen. Combined structural, spectroscopic, and theoretical evidence shows that the σ-dimer contains a weak C(sp3)–C(sp3) bond, but is stabilized against thermal dissociation by a very strong dispersive interaction between the overlapping π surfaces.

Conductive π-conjugated polymers were electrochemically generated from a variety of donor–acceptor pyrroles containing fused perimidine subunits. Alternating oxidative and reductive polarization of...

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.

Oxidative transformation of hexapyrrolylbenzenes into azacoronenes using bromine electrophiles as alternative coupling agents is shown to occur according to a distinct mechanism, different from those proposed for typical high-potential oxidants. It is shown that consecutive cyclizations do not involve brominated intermediates and can be rationalized by assuming a relayed arenium cation attack followed by deprotonation and conjugate elimination. The final cyclization is incompatible with this mechanism and is found to involve double-electrophilic bromination followed by thermal elimination of dibromine. These findings provide insight into the reactivity of sterically congested aromatic systems and may help in designing new methods of C-C bond formation.

International audience; A cycloparaphenylene-based molecular lemniscate (CPPL) was obtained in a short synthesis involving masked p-phenylene equivalents. The strained figure-eight geometry of CPPL is sustained by the incorporated 9,9'-bicarbazole subunit, which also acts as a stereogenic element. The shape of the distorted [16]cycloparaphenylene nanohoop embedded in CPPL is accurately approximated with a Booth lemniscate. The structure of CPPL, investigated using NMR and Raman spectroscopic methods, revealed strain-dependent features, consistent with the variable curvature of the ring. The electronic and optical properties of CPPL combine features more characteristic of smaller cycloparaphenylenes, such as a reduced optical bandgap and red-shifted fluorescence. CPPL was resolved into enantiomers, which are configurationally stable and provide strong chiroptical responses, including circularly polarized luminescence.

Purpose – The purpose of this article is identification and description of risks, which constitute an inherent element of the tax documentation. Design/Methodology/approach – This article includes monographic research methodology using information in qualitative and descriptive form. Analysis and logical structure method has been applied to the literature on the subject taking into account existing scope of the tax law. The practical part of this article includes case study. Findings – The research result is quantification of tax risks resulting from cooperation of related companies in the aspect of the transfer prices documentation. Originality/value – One of the elements of widely understood economic environment is the fiscal environment. The tax law which mainly serve to fiscal purposes, performs one of the basic tax system functions to which the fiscal function belongs. However, the tax law gives companies the opportunity to choose, for example, the form of cooperation especially between companies with capital, organizational and personal links. Business links significantly influence the opportunities of cooperation and at the same time they are a source of the tax risk. Identification and description of the tax risk in the aspect of reliability of the transfer prices documentation seems to be an important problem.

Specyfika dziel technicznych polega na tym, ze z zalozenia sluzą one realizacji celow pragmatycznych. Uzytkowy charakter dziel technicznych wplywa na proces ksztaltowania treści i formy utworu. Na „dzialalnośc tworczą o indywidulanym charakterze” mają wplyw takie okoliczności, jak ograniczenia technologiczne, przewidywalnośc spodziewanego rezultatu dzialalności czy praktyka postepowania. W konsekwencji dziela techniczne mozna przeciwstawic „klasycznie” pojmowanym utworom sluzącym zaspokojeniu potrzeb duchowych czlowieka. Analiza polskiej doktryny i orzecznictwa sądow polskich prowadzi do wniosku, ze o ile przeslanka dzialalności tworczej w przypadku dziel technicznych co do zasady bedzie spelniona, o tyle wątpliwe jest, na ile proces tworczy, stratyfikowany czynnikami obiektywnymi, pozwala na indywidualne uksztaltowanie dziela technicznego. W rezultacie kwestia ochrony prawnoautorskiej dziela technicznego w wiekszości przypadkow sprowadzac sie bedzie do odpowiedzi na pytanie, czy spelnia ono przeslanke indywidualnego charakteru utworu. Ustawowa przeslanka indywidulanego charakteru musi uwzgledniac kazdy przejaw dzialalności tworczej czlowieka, w tym taki, ktory nalezy do szeroko rozumianej sfery dziel niefikcjonalnych (dzielo techniczne, naukowe). W konsekwencji swoisty charakter dziel technicznych rodzi pytania zarowno o to, w jakim stopniu przeslanka indywidualności realizuje sie w przypadku dziel technicznych, jak i o to, jakie jest samo znaczenie indywidualnego charakteru utworu w polskim prawie autorskim.

The paper is aiming to determinate the extent of the north eastern arm of Kozłowicka buried valley on the grounds of own re search by means of electrical resistivity tomography- ERT and avail able archival researches. On the Hydro-geological map of Poland, Żyrardów sheet (Felter and Nowicki, 1998a, b) Kozłowicka buried valley was differentiated as an individual hydro-geological unit. The results of the anal y sis show that the ex tent of the structure, defined by its up per boundary, differs significantly from the one suggested on the sheet of Hydrogeological map of Poland. Since there was no data avail able in the north eastern part of the dis cussed arm of Kozłowicka buried valley, the northern boundary was defined only based on avail able geoelectrical sounding profiles (Czerwiñska, 1988; Topolewska, 2015). In order to confirm suggested solution, geoelectrical re search by means of electrical resistivity tomography (ERT) was con ducted. The measurements were per formed along 3 pro files located in the area of interest. The authors would like to point out the need of the us age of ERT in map ping and studying buried structures that might be ground water reservoirs. As a result, one obtains quasi-continuous image of electrical resistivity of the subsurface. Due to the contrast of electrical properties of sediments, it is possible to determine upper and bottom surfaces of buried structures, formed within glacial deposits.

The paper presents spatial analysis and numerical methods to describe the hydrodynamic and hydrochemical conditions in a groundwater system. The research was conducted in the northern part of the Białystok High Plane, eastern Poland, within a Quaternary multi-aquifer system. Spatial analysis was used for imaging the quasi-continuous structure of the system based on a discrete set of hydrogeological data. A high-resolution regional flow model was used to identify the groundwater discharge and discharge zones of the individual aquifers. Calculations have shown a marked asymmetry of the flow system. Deeply incised river valleys in the Niemen River basin more strongly affect the groundwater than the discharge zones in the valleys of the Vistula River basin. As a result, the underground watershed in deeper aquifers is clearly shifted westward in relation to the morphological watershed. The hydrodynamic conditions of the system determined by numerical methods were used to identify the points along the groundwater flow-path for the hydrochemical study. It was the basis for the identification of points located along the groundwater flow direction, which were used in the hydrochemical study. Computational schemes of water solution models were calculated for the quasi-equilibrium state of chemical reactions between the solution and the solid and gaseous phases. Presentation of the chemical reactions allowed determining the origin of changes in the concentrations of individual components dissolved in groundwater. It was found that kaolinitization, i.e. chemical weathering of feldspars and plagioclases is the basic process that most affects the groundwater chemistry.

[4]Chrysaorene, a fully conjugated carbocyclic coronoid, is shown to be a low-bandgap π-conjugated system with a distinct open-shell character. The system shows good chemical stability and can be oxidized to well-defined radical cation and dication states. The cavity of [4]chrysaorene acts as an anion receptor toward halide ions with a particular selectivity toward iodides (Ka = 207 ± 6 M–1). The interplay between anion binding and redox chemistry is demonstrated using a 1H NMR analysis in solution. In particular, a well-resolved, paramagnetically shifted spectrum of the [4]chrysaorene radical cation is observed, providing evidence for the inner binding of the iodide. The radical cation–iodide adduct can be generated in thin solid films of [4] chrysaorene by simple exposure to diiodine vapor.

1,n-Dipyrrolylalkanes can be efficiently converted into extensively π-conjugated bipyrroles by PdII-mediated annulative double C–H activation, and this approach might be further developed into tandem processes involving further cyclization of substituents or oxygenation of pyrrolic α-positions. Herein, the mechanism of these transformations is explored using NMR spectroscopy and DFT calculations. The kinetics of the annulation are found to depend on the conjugation extent and donor–acceptor character of the pyrroles, as well as on substitution and the linker length. Combined experimental and theoretical evidence indicates that a change of the rate-determining step occurs for the most electron-deficient substrates. The unprecedented double α-oxygenation of bipyrroles is found to be a stepwise process, involving α-acetoxylated intermediates.

A heteroaromatic nanographene containing a unique assembly of five-, six- and seven-membered rings is synthesized using oxidative coupling of an indole-containing precursor. Near-infrared absorption and emission properties of the nanographene core are enhanced by peripheral expansion and ring fusion at all oxidation levels. The dicationic state shows distinct aromaticity originating from a peripheral π-conjugated circuit. A partially coupled intermediate, trapped in the synthesis of the 5-6-7 nanographene, is explored as a reference system, showing an unexpected reduction of the optical band gap due to intramolecular charge transfer.

This paper discusses the problem of identification and measurement of logistics cost parameters in the accounting information system indicating their impact on business management processes. The first part of the study presents the identification and measurement of logistics costs from the perspective of broadly understood business management. The subsequent part of the paper exposes the results of the empirical research in the field of logistics costs analysis in the production company. The attention has been focused on the factors that improve management efficiency by the identification and implementation of control mechanisms of logistics costs in business management. The aim of the paper is to learn and assess the relationship existing between the level of analytical identification of logistics costs in the analyzed areas and the efficiency of management. The research methods applied to achieve the objective are literature studies, descriptive analysis and trend analysis of logistics costs. The research period covers the years 2013 – 2015. The problem of identification and measurement of logistics costs in the company is important and up-to-date on account of its impact on management processes in the area of business efficiency.

Nonclassical nanotube end-caps have been constructed from strain-free heterocyclic precursors using a one-step synthetic procedure, involving multiple nickel-mediated Ullmann couplings. These systems consist of tubular macrocyclic sections that are tightly capped on one side with a bridging benzene ring, forming deep, chemically accessible cavities. The end-caps are characterized by exceptionally high internal strain energies reaching 144 kcal/mol. The optical absorption and emission properties of these molecules show a marked dependence on conjugation length and geometrical factors. The mechanism of end-cap formation, investigated using DFT calculations, relies on precise timing of transmetalation and reductive elimination events.

An octaphyrin(1.2.1.1.1.2.1.1) containing two conjugated ethynylene bridges has been synthesized and characterized. The macrocycle reveals complex conformational dynamics dependent on its protonation and oxidation state. The [40]annulenoid macrocycle and its [38]annulenoid oxidized form display residual macrocyclic ring currents. In spite of its low apparent aromaticity the new octaphyrin is a potent chromophore with a vis-NIR absorption profile strongly influenced by the redox and acid–base chemistry.

Reaction of paraformaldehyde with meso-tetraaryl-2-aza-21-carbaporphyrins (NCP) in the presence of a basic catalyst afforded fused lactam derivatives comprising a >C═O bridge linking the internal carbon C21 with one of the internal nitrogens. The isomer 2 with C21-C(O)-N24 bridge is formed with about 9-fold molar excess over that with C21-C(O)-N22 bridge (3). The (1)H NMR and UV-vis spectral characteristics indicate aromatic character of the derivatives. For meso-tetrakis(3',5'-dimethoxy)- and meso-tetrakis(3',4',5'-trimethoxy)-21,24-carbonyl-NCP an efficient external ring fusion by linking C3, i.e., the external carbon of the confused pyrrole, with an ortho carbon of the adjacent aryl was observed under acidic conditions, yielding derivatives 4c and 4d, comprising a linear system of five fused rings. The chirality and configurational stability of these carbonylated systems were established by a chiral stationary phase HPLC and circular dichroism. The interaction of 2 with chiral acids and alcohols leading to the formation of diastereomers was observed by (1)H NMR. Slow racemization of 2 under acidic conditions was established by HPLC and (1)H NMR and a mechanism for this process was proposed.

Density functional theory calculations combined with a distortion/interaction energy analysis show that the anomalous Z selectivity observed in Wittig reactions of ortho-substituted benzaldehydes is not caused by phosphorus-heteroatom interactions in the addition transition state, as assumed in earlier work, but is predominantly steric in nature. The calculations reproduced correctly the stereoselectivity preferences for a wide range of reactant pairs as well as relative reactivities for different substituent types, providing deeper structural insight into the mechanism of Wittig olefination.

An electron-rich 3,4-diarylpyrrole is shown to undergo a tandem inter- and intramolecular Scholl oxidation, providing access to bis(phenanthropyrroles), a new class of bipyrrole derivatives with extended π conjugation. Intermolecular coupling of two pyrrole molecues is found to be the initial step of this reaction. Bis(phenanthropyrroles) are characterized by restricted rotation around the α-α bond and exhibit strong blue fluorescence and large Stokes shifts.

Two hitherto unknown core modified hexaphyrin analogues have been synthesized and characterized where the conformational dynamics of these macrocycles in the free base form is achieved by the rotation of thienothiophene units. Further unique property of these macrocycles is the Huckel-Mobius topological switching. The thermodynamic equilibrium and kinetics of the interconversion leading to Huckel-Mobius switches have been triggered by external stimuli, such as protonation and/or temperature. We have provided a thorough solution-state spectroscopic characterization, solid-state structural evidence combined with in-depth theoretical calculations to investigate the crucial factors involved in such interconversion between Huckel and Mobius topologies for these hexaphyrins which will be useful in designing future new members to expanded porphyrin chemistry.

22-hydroxybenziporphyrin, a porphyrin analogue containing a phenol moiety, has been shown to exist as an equilibrium mixture of two distinctly different tautomers. One of them actually contains the hydroxy group and shows the local [6]annulene aromaticity in the phenol fragment. The other tautomer contains a keto group and exhibits a [20]annulenoid structure characterized by macrocyclic antiaromaticity. The tautomerization process has been investigated in detail using variable-temperature 1H NMR spectroscopy. The process is very fast, with an estimated activation energy of ca. 30 kJ/mol. Further insight into the energetics of the tautomerization is obtained from density functional (DFT) calculations. Surprisingly, the estimated energy of the antiaromatic keto species is 3-5 kcal/mol lower than the energy of the phenolic tautomer. The geometric and magnetic manifestations of aromaticity and antiaromaticity in the two tautomers are probed using a number of computational devices, including Wiberg bond indices, resonace weights derived from the harmonic oscillator model, and nucleus-independent chemical shifts. It is shown that mixing of phenolic and keto contributions in both tautomers is stronger than that in related tautomers of phenol. This effect is caused by extensive conjugation with the tripyrrolic unit of 22-hydroxybenziporphyrin and, to a lesser extent, by intramolecular hydrogen bonding.

Z-Selective Wittig olefination was applied to the synthesis of large carbazolophanes containing up to eight heteroaromatic subunits. A number of strategies were devised and tested, showing that cyclooligomerization yields can be significantly improved by using one-component schemes involving heterobifunctional reactants. [4]- and [6]Carbazolophanes were characterized in the solid state, revealing compact, highly folded structures. Electronic and steric effects of substitution and chain length on the Wittig olefination rates and Z-selectivities were explored theoretically using DFT calculations.

A series of expanded porphyrins, incorporating biimidazoles and bipyrroles within their macrocyclic framework, has been synthesized. Insights into the complex conformational characteristics of these ems were obtained from two-dimensional NMR spectroscopic studies. The relative energy values for the various asymmetric structures inferred from these analyses were compared using DFT molecular modeling calculations.Key words: macrocycles, expanded porphyrins, imidazoles, pyrroles, biimidazoles, supramolecular chemistry, heterocycles.

The symmetry of the arrangement of objects has fascinated philosophers, artists and scientists for a long time, and still does. Symmetries often exist in nature, but are also created artificially, for instance by chemical synthesis of novel molecules and materials. The one-sided, non-orientable Möbius band topology is a paradigm of such a symmetry-based fascination. In the early 1960s, in synthetic organic chemistry the interest in molecules with Möbius symmetry was greatly stimulated by a short paper by Edgar Heilbronner. He predicted that sufficiently large [n]annulenes with a closed-shell electron configuration of 4n π-electrons should allow for sufficient π-overlap stabilization to be synthesizable by twisting them with a 180° phase change into the Möbius symmetry of their hydrocarbon skeleton. In 2007, the group of Lechosław Latos-Grażyński succeeded in synthesizing the compound di-p-benzi[28 ]hexa-phyrin(1.1.1.1.1.1), compound 1, which can dynamically switch between Hückel and Möbius conjugation depending, in a complex manner, on the polarity and temperature of the surrounding solvent. This discovery of “topology switching” between the two-sided (Hückel) and one-sided (Möbius) molecular state with closed-shell electronic configuration was based primarily on the results of NMR spectroscopy and DFT calculations. The present EPR and ENDOR work on the radical cation state of compound 1 is the first study of a ground- state open-shell system which exhibits a Hückel–Möbius topology switch that is controlled by temperature, like in the case of the closed-shell precursor. The unpaired electron interacting with magnetic nuclei in the molecule is used as a sensitive probe for the electronic structure and its symmetry properties. For a Hückel conformer with its higher symmetry, we expect – and observe – fewer ENDOR lines than for a Möbius conformer. The ENDOR results are supplemented by and in accordance with theoretical calculations based on density functional theory at the ORCA level.

A 3-phosphonated N-confused phlorin 3 was synthesized by the reaction of N-confused porphyrin 1 and trimethyl or triethyl phosphite 2 in the presence of acetic acid in good yield. The presence of hydrogen and aryl substituents in one of the meso positions (C5) generates a stereogenic center, resulting in configurationally stable enantiomers. The enantiomers were separated by HPLC and characterized by the circular dichroism method for the first time in the case of phlorin. Further oxidation of 3 by DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone) afforded the achiral 3-phosphonated N-confused porphyrin 4. Chiral chlorozinc 4-Zn and chlorocadmium 4-Cd, as well as achiral nickel(II) complexes 4-Ni were also characterized. For 4-Cd in the solid state, formation of a dimer consisting of heterochiral subunits joined by two H-bonds was established by a single crystal X-ray analysis. For 4-Cd, separation of enantiomers was achieved. Slow racemization of 4-Cd in solution prevented the absolute configuration determination by the X-ray method indicating the labile character of the complex. The relationship between circular dichroism and absolute configuration of 3a and 4-Cd was established on the basis of TD-DFT calculations.