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In one pot, tertiary alkyl amines are oxidized to enamines by cationic dioxa[6]helicene, which further reacts as electrophile and oxidant to form mono or bis donor‐π‐acceptor coupling products. This original and convergent synthetic approach provides a strong extension of conjugation yielding chromophores that absorb intensively in far‐red or NIR domains (λmax up to 791 nm) and fluoresce in the NIR as well (λmax up to 887 nm). Intense ECD properties around 790 nm with a |Δϵ| value up to 60 M−1 cm−1 are observed. [ABSTRACT FROM AUTHOR]

The dynamic interplay between two types of chiral structures; fully conjugated racemic hetero[7]helicenes and DNA strands prone to fold into G‐quadruplex structures is described. Both the [7]helicenes and the G‐quadruplex DNA structures exist in more than one conformation in solution. We show that the structures interact with and stabilise each other, mutually amplifying and stabilising certain conformations at increased temperatures. The [7]helicene ligands L1 and L2 stabilise the parallel conformation of k‐ras significantly, whereas hybrid (K+) and antiparallel (Na+) h‐telo G‐quadruplexes are stabilised upon conformational switching into altered G‐quadruplex conformations. Both L1 and L2 induce parallel G‐quadruplexes from hybrid structures (K+) and L1 induces hybrid G‐quadruplexes from antiparallel conformations (Na+). Enantioselective binding of one helicene enantiomer is observed for helicene ligand L2, and VTCD melting experiments are used to estimate the racemisation barrier of the helicene. [ABSTRACT FROM AUTHOR]

We achieved a two‐type synthesis of quinoxaline‐fused polyaza[5]‐ and [7]helicenes through consecutive N−H/C−H coupling with a hypervalent iodine reagent as a key reaction. By fusing electron‐deficient quinoxaline, these polyazahelicenes constitute an efficient donor‐acceptor type of molecule with absorption edges that reach up to approximately 650 nm. Evaluating the chiroptical properties reveals that the polyazahelicene exhibits a rare orange circularly polarized glow with a luminescence dissymmetry factor (glum value) of 0.003. [ABSTRACT FROM AUTHOR]

A series of multiple helicenes was simultaneously synthesized in one step by intramolecular cyclization of a single chrysene derivative containing two 2‐[(4‐alkoxyphenyl)ethynyl]phenyl units accompanied by rearrangements of the aryl pendants. The electrophile‐induced double cyclization with or without aryl migrations proceeded efficiently under acidic conditions to afford annulative π‐extension of the chrysene units and produced quadruple (QH‐2), triple (TH‐2), and double (DH‐2) helicenes containing [4]‐ and/or [5]helicene frameworks with dynamic and/or static helicene chirality in one step. Three multiple helicenes' structures were determined by X‐ray crystallography and/or density functional theory calculations. The multiple TH‐2 and DH‐2 helicenes were separated into enantiomers because of the stable one and two [5]helicene moieties, respectively, and showed intense circular dichroism and circularly polarized luminescence. Although QH‐2, which comprises four [4]helicene subunits, was not resolved into enantiomers, the TH‐2 enantiomers were further separated into a pair of diastereomers at low temperature resulting from their substituted [4]helicene chirality. [ABSTRACT FROM AUTHOR]

We report a new family of hexa‐peri‐hexabenzocoronene (HBC)‐based helical nanographenes incorporating π‐extended carbo[5]helicenes bearing an octagonal carbocycle. This family represents a new kind of highly distorted saddle‐helix hybrid nanographenes. For the first time, the eight‐membered ring becomes a constituent of both a carbo[5]helicene and a HBC and thus, the negative curvature is responsible for twisting both units. This novel chiral motif, namely, oct‐[5]helicene results in the largest torsion angle recorded so far for a carbo[5]helicene (θ=79.5°), as it has been suggested by DFT‐calculations and confirmed by X‐ray crystallography. Consequently, the barriers of isomerization become exceptionally high for a [5]helicene unsubstituted in the fjord region since neither racemization nor decomposition were observed at 200 °C for 1 or 3 during 5 h. Therefore, racemic resolutions allowed subsequent chiroptical studies showing the ECD and CPL responses of this novel family of chiral nanographenes. [ABSTRACT FROM AUTHOR]

The intramolecular Diels−Alder reactions of helicenes deform their π‐conjugated screw‐shaped skeletons. In particular, terminally tetrafluorinated [7]helicene (F4‐[7]helicene) undergoes a photoinduced Diels−Alder reaction followed by a photoinduced double fluorine atom transfer. Herein, we thoroughly investigated this photochemical domino process by decreasing the level of fluorine substitution. F3‐[7]Helicenes bearing two fluorine atoms at the dienophile terminal underwent photoinduced Diels−Alder reactions, but the whole domino process became slow. F2‐[7]Helicene, which is difluorinated only at the dienophile terminal, was also photolabile. As a result, two fluorine atoms were sufficient for the photochemical domino reaction to occur. X‐ray crystallographic analysis revealed that F2‐[7]helicene was less compressed than F4‐[7]helicene, indicating that terminal polyfluorination enhanced the intramolecular arene−fluoroarene stacking interactions and thus promoted the transformations. [ABSTRACT FROM AUTHOR]

Helicenes represent an important class of chiral organic material with promising optoelectronic properties. Hence, functionalization of surfaces with helicenes is a key step towards new organic material devices. This review presents different aspects of adsorption and modification of metal surfaces with different helicene species. Topics addressed are chiral crystallization, that is, 2D conglomerate versus racemate crystallization, breaking of mirror-symmetry in racemates, chirality-induced spin selectivity, and stereoselective on-surface chemistry., (© 2024 The Author(s). Chirality published by Wiley Periodicals LLC.)

A homologous series of 4,7-bis(aryl) substituted benzothiadiazole (BTD) compounds, containing the helicenic derivatives bis([4]helicene), bis([5]helicene) and bis([6]helicene), have been prepared upon a double Suzuki coupling between 3,6-bis(pinacolyl-borane)-BTD and the corresponding bromo-aryl precursors. The single crystal X-ray structure of the bis([4]helicene) compound shows the existence of both helicities (M) and (P) on the same molecule. All the compounds of the series are highly emissive in solution, with quantum yields of the emission ranging from 50 to 91 %. The enantiopure compounds (M,M) and (P,P) for the BTD-bis([6]helicene) have been prepared from the corresponding enantiopure 2-bromo-[6]helicene precursors. Their chiroptical properties have been investigated in correlation with density functional theory (DFT) calculations, which allowed to confidently assign the absolute configuration of the helicene arms and to characterize the different electronic transitions, including the low energy charge transfer excitation from helicenes to BTD. The enantiomerically pure fluorophores (M,M)- and (P,P)-BTD-bis([6]helicene), which exist in solution as two main conformers, according to the DFT calculations, show CPL activity in solution, with g lum factors of ≈1.7×10 -3 at λ em =525 nm, and also in the solid state, with g lum factors of ≈1.2×10 -3 in spite of the strong decrease of the quantum efficiency., (© 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Although helicenes are promising molecules, the synthetic difficulty and tediousness have often been problems, and only small amounts of optically pure helicenes have been obtained by using chiral HPLC in most cases. Herein, aza[7]helicenes or closed-aza[7]helicenes with (1R)-menthyl substituents were selectively synthesized via the intramolecular Scholl reaction, and the diastereomeric pairs were separated by silica gel column chromatography. The optically pure helicenes were further transformed into the corresponding cyclic dimers, and the chiroptical properties were investigated. The rigid π-frameworks of the dimers led to the high molar extinction coefficients and fluorescence quantum yields, while the twisted helicene moieties induced clear Cotton effects and CPL in the visible region, and the high CPL brightness (B CPL ) was achieved. Furthermore, the cyclic dimers were found to have the macrocyclic cavity with the two NH groups suitable for the selective binding of a fluoride anion, which induced significantly redshifted fluorescence and CPL in the red region., (© 2024 Wiley-VCH GmbH.)

This combined experimental and theoretical study illustrates the profound consequences of non-planarity on the electronic properties of polycyclic arenes. Three isomeric [10]fibonacene tetraesters were synthesized through a robust and regiocontrolled Perkin/Mallory approach: a nearly planar [10]phenacene derivative, a moderately twisted [10]semicircle derivative, and a 3D non-planar [10]helicene derivative. The photophysical properties of the 3D [10]helicene isomer were found to be dramatically different from the comparable ones of the [10]phenacene and [10]semicircle isomers. The aromatic properties of the [10]phenacene and [10]semicircle isomers conform well with their predictive Kekulé and Clar analyses, but the [10]helicene isomer deviates from these general topological rules, which appears to be a general phenomenon for [n]fibonacenes with n≥9., (© 2024 Wiley-VCH GmbH.)

The most important stereodynamic feature of carbo[n]helicenes is the interconversion of their enantiomers. The Gibbs activation energy (ΔG≠(T)) of this process, which determines the rate of enantiomerization, dictates the configurational stability of [n]helicenes. High values of ΔG≠(T) are required for applications of functional chiral molecules incorporating [n]helicenes or helicene substructures. This minireview provides an overview of the mechanism, recent developments, and factors affecting the enantiomerization of [n]helicenes, which will accelerate the design process of configurationally stable functional chiral molecules based on helicene substructures. Additionally, this minireview addresses the misconception and irregularities in the recent literature on how the terms "racemization" and "enantiomerization" are used as well as how the activation parameters are calculated for [n]helicenes and related compounds. [ABSTRACT FROM AUTHOR]

The cyanuric acid (CA) heterocycle forms supramolecular structures with adenine nucleobases/nucleosides and oligonucleotides, leading to speculation that they can act as forerunners to RNA. Herein, the assembly behavior of RNA containing CA and CA–ribose nucleoside was studied. Contrary to previous reports, CA in RNA and the CA‐ribonucleoside resulted in destabilization of supramolecular assemblies, which led to a reevaluation of the CA–adenine hexameric rosette structure. An unprecedented noncovalent supramolecular helicene structure is proposed to account for the striking difference in behavior, which has implications for novel paradigms for reorganizing the structures of nucleic acids, the synthesis of long helicenes, and pre‐RNA world paradigms. The results caution against extrapolating the self‐assembly behavior of individual heterocycles from the level of monomers to oligomers because the base‐paring properties of (non‐)canonical nucleobases are impacted by the type of oligomeric backbone to which they are attached. [ABSTRACT FROM AUTHOR]

Two types of helically chiral compounds bearing one and two boron atoms were synthesized by a modular approach. Formation of the helical scaffolds was executed by the introduction of boron to flexible biaryl and triaryl derived from small achiral building blocks. All‐ortho‐fused azabora[7]helicenes feature exceptional configurational stability, blue or green fluorescence with quantum yields (Φfl) of 18–24 % in solution, green or yellow solid‐state emission (Φfl up to 23 %), and strong chiroptical response with large dissymmetry factors of up to 1.12×10−2. Azabora[9]helicenes consisting of angularly and linearly fused rings are blue emitters exhibiting Φfl of up to 47 % in CH2Cl2 and 25 % in the solid state. As revealed by the DFT calculations, their P–M interconversion pathway is more complex than that of H1. Single‐crystal X‐ray analysis shows clear differences in the packing arrangement of methyl and phenyl derivatives. These molecules are proposed as primary structures of extended helices. [ABSTRACT FROM AUTHOR]

Minimum energy structures of neutral and radical cations of end‐substituted thia[n]helicenes (n = 1‐10) in DCM solvent are reported. For both neutral and radical cations of these helicenes, calculated structures are nonplanar for n = 3 to 10. Helical structures are obtained for higher helicenes, and the thia[8]helicene system has a helical structure with one complete turn. Equilibrium structures are predicted by using B3LYP‐D/6‐311++G(d,p) method in conjunction with the solvation model based on solute density. Single‐point energy calculations are also performed at the MP2 level to improve certain energy parameters. Excited‐state calculations are performed using time‐dependent density functional theory formalism to predict UV‐Visible spectra of neutral and radical cations of thia[n]helicenes in DCM solvent. Thia[n]helicenes radical cation have strong absorption in the near‐infrared region. Calculations also suggest that dimerization is not a favorable process in the DCM solvent for the end‐substituted neutral and radical cation of thia[7]helicene. The present theoretical study examines the molecular and electronic properties of thia[n]helicenes in search of near‐infrared electronic devices. [ABSTRACT FROM AUTHOR]

The synthesis of an unprecedented, π‐extended hexabenzocorene (HBC)‐based diaza[7]helicene is presented. The target compound was synthesized by an ortho‐fusion of two naphthalene diimide (NDI) units to a HBC‐skeleton. A combination of Diels–Alder and Scholl‐type oxidation reactions involving a symmetric di‐NDI‐tolane precursor were crucial for the very selective formation of the helical superstructure via a hexaphenyl‐benzene (HPB) derivative. The formation of the diaza[7]helicene moiety in the final Scholl oxidation is favoured, affording the symmetric π‐extended helicene as the major product as a pair of enantiomers. The separation of the enantiomers was successfully accomplished by HPLC involving a chiral stationary phase. The absolute configuration of the enantiomers was assigned by comparison of circular dichroism spectra with quantum mechanical calculations. [ABSTRACT FROM AUTHOR]

Solid‐state packing plays a defining role in the properties of a molecular organic material, but it is difficult to elucidate in the absence of single crystals that are suitable for X‐ray diffraction. Herein, we demonstrate the coupling of divergent synthesis with microcrystal electron diffraction (MicroED) for rapid assessment of solid‐state packing motifs, using a class of chiral nanocarbons—expanded helicenes—as a proof of concept. Two highly selective oxidative dearomatizations of a readily accessible helicene provided a divergent route to four electron‐deficient analogues containing quinone or quinoxaline units. Crystallization efforts consistently yielded microcrystals that were unsuitable for single‐crystal X‐ray diffraction, but ideal for MicroED. This technique facilitated the elucidation of solid‐state structures of all five compounds with <1.1 Å resolution. The otherwise‐inaccessible data revealed a range of notable packing behaviors, including four different space groups, homochirality in a crystal for a helicene with an extremely low enantiomerization barrier, and nanometer scale cavities. [ABSTRACT FROM AUTHOR]

Efficient and versatile synthetic routes to functionalized tetrathia[7]helicenes (7‐THs) are described. The key intermediates of these methodologies are 2‐bromo‐3,3′‐bibenzo[1,2‐b:4,3‐b′]dithiophenes (1), synthesized through a palladium‐catalyzed homocoupling reaction between two benzo[1,2‐b:4,3‐b′]dithiophene units followed by a regioselective α‐bromination. Direct palladium‐catalyzed annulation of bromides 1 with internal alkynes provides a set of 7,8‐disubstituted 7‐THs 2 in moderate to good yields (46‐80 %). Otherwise, 7‐monosubstituted 7‐THs 4 have been prepared through Sonogashira coupling of 1 with terminal alkynes, followed by platinum‐ or indium‐promoted cycloisomerization of alkynyl intermediates 6. Finally, the versatility of bromides 1 has also been demonstrated by using them for the preparation of benzo (hetero) fused 7‐TH derivatives 7 via Suzuki coupling with (hetero)arylboronic acids and the photocyclization of the obtained intermediates 9. [ABSTRACT FROM AUTHOR]

The interaction between the silver ion and the cyclic aromatic molecules, namely, the helicenes, is the subject of this paper. In fact, a silver complexation system based on quartz crystal microbalance (QCM) sensor with a functional film of helicenes has been designed and developed at four temperatures. The developed system, in which the sensor response reflects the adsorption of the hexahelicene and the heptahelicene, was able to control the complexed mass of silver for each concentration. Experimental outcomes indicated that the quartz crystal coated with heptahelicene is the adequate material for silver adsorption. Then, a theoretical study has been performed through two statistical physics models (SMPG and SMRG) in order to analyze the experimental adsorption isotherms of the two helicenes at the ionic scale. The SMRG model was developed using the real gas law and was satisfactorily applied for the microscopic investigation of the hexahelicene isotherms indicating that the lateral interactions between the adsorbates are responsible of the decrease of the adsorbed quantity at saturation. The interpretation of the two models' parameters indicated that the adsorption of the two helicenes is an endothermic phenomenon. Interestingly, the heptahelicene is recommended for silver complexation because it shows the highest adsorption energies involving chemical bonds during the complexation process. The SMPG model and the SMRG model also allow prediction of three thermodynamic functions (configurational entropy, Gibbs free enthalpy, and internal energy) which govern the adsorption mechanism of silver on the two helicenes. [ABSTRACT FROM AUTHOR]

Herein, we report a simple and efficient approach to synthesize a functionalized 2,18‐dimethoxy‐5,10,15‐trioxa[9]helicene. It was synthesized from simple phenol building blocks using two subsequent reactions namely oxidative coupling and dehydrative cyclization or palladium mediated cyclization. The molecular integrity of the helical core was determined by single‐crystal X‐ray diffraction and NMR techniques. Its crystal structure showed the spontaneous resolution which was attributed to the conglomerate formation of the same helical isomer via C−H⋅⋅⋅O and π⋅⋅⋅π or H⋅⋅⋅π interactions. Then, it was converted to racemic 2,18‐dihydoxy‐5,10,15‐trioxa[9]helicene. Enantiomers were separated on preparative HPLC with high optical purity (>99 % ee). Based on electronic circular dichroism, the absolute configurations of dextrorotary and levorotatory antipodes were assigned as P and M, respectively. We also studied the absorption, emission and chiroptical behavior of these helical compounds in the solution state. [ABSTRACT FROM AUTHOR]

De nouveaux [4]hélicènes fonctionnels ont été conçus et synthétisés, avec des rendements globaux de 54%--72%, selon une approche photochimique opérationnelle et simple en deux étapes à partir de divers phénylacétonitriles p-substitués et ont été caractérisés par RMN (1H, 13C et COSY) et IR à transformée de Fourier. Les propriétés d'absorption UV--Vis de ces systèmes tétracycliques conjugués ont été étudiées expérimentalement dans divers solvants et leur énergie de gap optique a été estimée à moins de 3.28 eV. Les propriétés de photoluminescence de ces molécules ont été évaluées en solution et une émission a été notée dans la région bleue du spectre visible. Les résultats obtenus semblent encourageants pour l'examen de tels composés en tant que matériaux prometteurs pour des applications optoélectroniques. [ABSTRACT FROM AUTHOR]

Described herein is a strategy to construct cationic azahelicenes through the three‐component annulation reaction of isoquinoline, indole, and 1,2‐dichloroethane (DCE), in which DCE serves as an in situ activating agent for C1−H activation of isoquinoline, a vinyl equivalent, and a solvent. This in situ activation annulation reaction features a facile one‐step synthesis and complete regioselectivity. The complete regioselectivity of C1 over C3 for the isoquinoline ring paves a path to the helical structure in a highly ordered sequence. One of the synthesized ionic [5]azahelicenium fluorophores exhibits the potential to serve as a mitochondria‐targeted biomarker with good photostability and low cytotoxicity. [ABSTRACT FROM AUTHOR]

The synthesis of unprecedented BINOL‐derived cationic phosphonites is described. Through the use of these phosphanes as ancillary ligands in AuI catalysis, a highly regio‐ and enantioselective assembly of appropriately designed alkynes into 1‐(aryl)benzo[5]carbohelicenes is achieved. The modular synthesis of these ligands and the enhanced reactivity that they impart to AuI‐centers after coordination have been found to be the key features that allow an optimization of the reaction conditions until the desired benzo[5]helicenes are obtained with high yield and enantioselectivity. [ABSTRACT FROM AUTHOR]

Helicenes and extended helical π‐conjugated compounds have been widely studied, but most of the systems contain only aromatic benzene or heterocyclic rings, showing local aromatic character. Herein, new S‐shaped double [6]helicene 1, which has two embedded para‐quinodimethane (p‐QDM) units, is reported. Due to the existence of a proaromatic quinoidal substructure, it has open‐shell diradical character. Its model compound, C‐shaped single [6]helicene 2 containing one p‐QDM unit, was also synthesized and compared. Their ground‐state structures and electronic properties were systematically studied by a combination of various experimental methods assisted by theoretical calculations. Compound 1 has a double‐helical structure in the crystal, with the two terminal [6]helicene units bent in opposite directions (i.e. anti form). However, an anti/syn isomerization process with a moderate interconversion energy barrier was observed on the NMR timescale. Compound 1 shows amphoteric redox behavior. It also exhibits open‐shell diradical character (y0=12.1 %) and a small singlet–triplet gap. On the other hand, compound 2 has a typical closed‐shell nature. The dication and dianion of 1 also show open‐shell diradical character. The dianion of 2 and the tetraanion of 1 exhibit similar electronic structures to their respective isoelectronic structures, that is, [6]helicene and a double [6]helicene. This work provides some insights into the design and synthesis of stable helical π systems with open‐shell diradical character and magnetic activity. [ABSTRACT FROM AUTHOR]

The synthesis of a new type of chiral and dynamic nonplanar aromatics containing a combination of fused perylene‐based coronenes and helicenes is reported. Either one or two helicene moieties were fused to the bay regions of an extended perylene core. The target compounds contain either identical or two different helicene building blocks. The combination with two helicene units leads to six different isomers, including two pairs of enantiomers and two meso forms. The experimental determination of the isomerization barriers the corresponding double [5]‐helicenes revealed activation energies of Ea=24.81 and 25.38 kcal mol−1, which is slightly above the barrier of the parent [5]‐helicene. Resolution of all possible regio‐ and stereoisomers allowed for the systematic investigation of the chiroptical properties. They revealed remarkable dissymmetry factors IgabsI of up to 1.2×10−2, which mirror the synergy between the strong absorbing perylenes and the inherent chirality of helicenes. [ABSTRACT FROM AUTHOR]

By attaching pyridine groups to a diaza[6]helicene, a helical, bis‐ditopic, bis‐N N‐coordinating ligand can be accessed. Dinuclear rhenium complexes featuring this bridging ligand, of the form [{Re(CO)3Cl}2(N N−N N)], have been prepared and resolved to give enantiopure complexes. These complexes are phosphorescent in solution at room temperature under one‐ and two‐photon excitation. Their experimental chiroptical properties (optical rotation, electronic circular dichroism and circularly polarized emission) have been measured. They show, for instance, emission dissymmetry factors of c.a. ±3x10−3. Quantum‐chemical calculations indicate the importance of stereochemistry on the optical activity, pointing towards further design improvements in such types of complexes. [ABSTRACT FROM AUTHOR]

Self‐catalysis is defined as catalysis by a product of a chemical reaction, that causes a significant increase in reaction rate in terms of the progress of the reaction. When a self‐catalytic reaction is involved in a reversible nonequilibrium‐to‐equilibrium chemical reaction, notable kinetic phenomena appear including sigmoidal kinetics, the seeding effect, thermal hysteresis, and chiral symmetry breaking. The nature of self‐catalytic reactions is characterized by microscopic mechanisms involving pathways of molecular structural changes and by macroscopic mechanisms involving molecular flux. Reversible self‐catalytic reactions, which exhibit notably high sensitivity to environmental changes, are also observed. In this Review, reversible self‐catalytic reactions of helicene oligomer foldamers during formation of homo‐ and hetero‐double‐helices are discussed, which exhibit the properties outlined above. [ABSTRACT FROM AUTHOR]

Chiral helicenes that have helical π‐conjugated frameworks comprised of ortho‐fused aromatic rings have been intensively investigated for several decades owing to their attractive properties and high potential for a variety of applications. In contrast, studies concerning helicene radicals (open‐shell helicenes) formed by redox reactions have been severely limited due to inherent high reactivity of organic radicals. However, open‐shell helicenes possessing a combination of chirality and unpaired electron spin(s) delocalized on helical π‐conjugated orbital(s) are promising for novel synergic magnetic functions. Recently, several kinds of isolable air‐stable helicene radicals have been prepared to enable their detailed analysis of the crystal structures and physicochemical properties. This Minireview describes the recent advances and future prospects of organic‐based helicene radicals categorized into three groups: 1) ionic radicals, 2) neutral radicals, and 3) diradicals. [ABSTRACT FROM AUTHOR]

Chirality is a fascinating phenomenon for recent electrochemistry and materials research, allowing for the preparation of detection platforms based on analyte enantiodiscrimination and the development of advanced chiroptical devices and chiral electrodes. In this Viewpoint, we highlight new directions in the field of chiral helical polyaromatic molecules (mainly helicenes) that are useful for the preparation of optically and redox‐active polymers and/or self‐assembled thin layers, nanostructures and functional electrode surfaces. Instead of the previously reported chiral materials prepared by molecular imprinting, a concept based on the preparation of inherently chiral helicene‐based materials with (opto)electrochemical applicability is presented. A short overview of well‐established electrochemical methods for the research of chiral molecules is also outlined. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons consisting of three fused anthracene units were designed as new π‐conjugated compounds having helical structures. These expanded helicenes were synthesized by Pt‐catalyzed cycloisomerization of the corresponding ethynyl‐substituted precursors. The nonplanar and helical structure was confirmed by X‐ray analysis and DFT calculations, and the barrier to helical inversion was estimated to be 34 kJ mol−1. The enantiomers of the diphenyl derivative were successfully resolved by chiral HPLC. Enantiopure samples showed good chiroptical performance in the CD (|Δϵ| 1380 L mol−1 cm−1) and CPL (|glum| 0.013) spectra, and these values were considerably large for simple organic molecules. The unique chiroptical properties are discussed on the basis of the molecular structure and the electronic state with the aid of time‐dependent DFT calculations. [ABSTRACT FROM AUTHOR]

Asymmetric pallada‐electrocatalyzed C−H olefinations were achieved through the synergistic cooperation with transient directing groups. The electrochemical, atroposelective C−H activations were realized with high position‐, diastereo‐, and enantio‐control under mild reaction conditions to obtain highly enantiomerically‐enriched biaryls and fluorinated N−C axially chiral scaffolds. Our strategy provided expedient access to, among others, novel chiral BINOLs, dicarboxylic acids and helicenes of value to asymmetric catalysis. Mechanistic studies by experiments and computation provided key insights into the catalyst's mode of action. [ABSTRACT FROM AUTHOR]

In recent papers, it is found that the silver-[6]Helicene complex can be used as a cancer drug but the interaction silver-hexaHelicene has not yet proven. The idea of this paper is to investigate the complexation process of the [6]Helicene by the silver metal (Ag+) using three types of adsorbates. Indeed, the adsorption of silver chloride, silver nitrate and silver sulfide into the sensor films deposited on the QCM electrode are measured at three temperatures (293–333 K). Films of the [6]Helicene were deposited on the QCM resonators using spin coating method in order to obtain uniform and homogenous sensor surface. Experimental results indicated that the [6]Helicene can form a stable complex with the silver ion and that the AgCl is the appropriate adsorbate for the complexation achievement. Actually, an advanced modeling analysis by means of statistical physics adsorption models is applied to explore the new vision of the complextion system. The values of the models parameters are deduced from fitting the experimental data with the developed models. They result in confirming the experimental findings by comparing the complexation energies of the three examined systems. In particular, for the silver nitrate, the Van-der-Waals parameters explained the isotherms drop at high concentration through the lateral interactions between the adsorbates. The adsorption energies analysis showed the highest interaction AgCl-[6]Helicene. Density functional theory (DFT) simulations showed that chemical bonds take place during the adsorption of silver chloride on hexaHelicene which confirms that the [6]Helicene can function as a chiral molecular tweezer of the univalent cationic silver. [ABSTRACT FROM AUTHOR]

The first enantiopure chiral‐at‐rhenium complexes of the form fac‐ReX(CO)3(:C^N) have been prepared, where :C^N is a helicene‐N‐heterocyclic carbene (NHC) ligand and X=Cl or I. These have complexes show strong changes in the emission characteristics, notably strongly enhanced phosphorescence lifetimes (reaching 0.7 ms) and increased circularly polarized emission (CPL) activity, as compared to their parent chiral models lacking the helicene unit. The halogen along with its position within the dissymmetric stereochemical environment strongly affect the photophysics of the complexes, particularly the phosphorescence quantum yield and lifetime. These results give fresh insight into fine tuning of photophysical and chiroptical properties of Re‐NHC systems. [ABSTRACT FROM AUTHOR]

Helical carbazole‐based BODIPY analogues were readily synthesized via aza[7]helicenes. The structures of azahelicene‐incorporated BF2 dyes were elucidated by x‐ray diffraction analysis. DFT calculations revealed that the π‐conjugated system expanded from the helicene moiety to the BODIPY framework. The azahelicene‐fused boron complexes showed the Cotton effects and the circularly polarized luminescence (CPL) in the visible region. Furthermore, an axially chiral binaphthyl group was attached to the helically chiral dyes, which enhanced the chiroptical properties. [ABSTRACT FROM AUTHOR]

A new family of distorted ribbon‐shaped nanographenes was designed, synthesized, and their optical and electrochemical properties were evaluated, pointing out an unprecedented correlation between their structural characteristics and the two‐photon absorption (TPA) responses and electrochemical band gaps. Three nanographene ribbons have been prepared: a seven‐membered‐ring‐containing nanographene presenting a tropone moiety at the edge, its full‐carbon analogue, and a purely hexagonal one. We have found that the TPA cross‐sections and the electrochemical band gaps of the seven‐membered‐ring‐containing compounds are higher and lower, respectively, than those of the fully hexagonal polycyclic aromatic hydrocarbon (PAH). Interestingly, the inclusion of additional curvature has a positive effect in terms of non‐linear optical properties of those ribbons. [ABSTRACT FROM AUTHOR]

This work describes a synthetic approach where a non‐planar aromatic heterocyclic [7]helicene is compressed to yield a hetero[8]circulene containing an inner antiaromatic cyclooctatetraene (COT) core. This [8]circulene consists of four benzene rings and four heterocyclic rings, and it is the first heterocyclic [8]circulene containing three different heteroatoms. The synthetic pathway proceeds via a the flattened dehydro‐hetero[7]helicene, which is partially a helicene and partially a circulene: it is non‐planar and helically chiral as helicenes, and contains a COT motif like [8]circulenes. The antiaromaticity of the COT core is confirmed by nucleus independent chemical shift (NICS) calculations. The planarization from a helically π‐conjugated [7]helicene to a fully planar heterocyclic [8]circulene significantly alters the spectroscopic properties of the molecules. Post‐functionalization of the [7]helicenes and the [8]circulenes by oxygenation of the thiophene rings to the corresponding thiophene‐sulfones allows an almost complete fluorescence emission coverage of the visible region of the optical spectrum (400–700 nm). [ABSTRACT FROM AUTHOR]

The partial fluorination of polycyclic aromatic hydrocarbons often produces a layered crystal packing, where fluorinated aromatic surfaces are stacked over nonfluorinated aromatic surfaces. Herein, we report the synthesis and crystal packing of partially fluorinated [4]helicenes with steric congestion resulting from H and F atoms in the fjord region. F6‐[4]Helicene forms head‐to‐tail columnar stacks consisting of an alternate arrangement of perfluorinated and nonfluorinated naphthalene moieties. With decreasing fluorine content, aromatic stacking switched from arene−fluoroarene (ArH−ArF) hetero‐stacking to ArH−ArH/ArF−ArF homo‐stacking with the help of intermolecular C−H⋅⋅⋅F contacts in the fjord region. As a result, head‐to‐head columnar stacks appear. Therefore, the conventional ArH−ArF stacking motif is not always applicable to Fn‐[4]helicenes with twisted π‐surfaces. [ABSTRACT FROM AUTHOR]

A series of indole-based helicenes, namely, 15-hexyl-15Htetraphenyl[1,2-e]indole (HTPI), 14-hexyl-14H-benzo[4’,5’]thieno [2’,3’:7,8]naphtha[1,2-e]indole (HBTNI), 7-hexyl-7H-indolo[5,4-k] phenanthridine (HIPD) and 3-hexyl-3H-phenanthro[4,3-e]indole (HPI) were successfully synthesized by three- or four-step reactions. They exhibited good solubility and high thermal stability of Td=247, 388, 294 and 251°C, respectively. These compounds emit violet-blue light with maximum emission peaks at 415, 397, 397 and 391 nm in hexane. Among them, HBTNI had excellent thermal stability, narrow and sharp emission peaks, and highest photoluminescence quantum yield (0.32). Thus, HBTNI was an ideal candidate for the violet-blue emitters of OLEDs. Furthermore, the four compounds had twophoton absorption and two-photon excited fluorescence. HTPI showed the maximum TPA with the TPA cross-section (δ) of 171.5 GM at 770 nm. They were rare examples of helicenes with both violet-blue emission and TPA. [ABSTRACT FROM AUTHOR]

Helicenes fused with hexafluorocyclopentene (HFCP) were synthesized by oxidative photocyclization of stilbene derivatives (the Mallory reaction). Of the newly‐obtained fluorinated helicenes, the [7]helicenes bearing one‐ or three‐HFCP units were structurally characterized by X‐ray crystallographic analysis. The attempted synthesis of [9]helicene fused with three HFCP units resulted in the unexpected formation of a novel double helicene consisting of [4]‐ and [6]‐helicenes sharing peripheral benzene rings. Optical properties and chiral resolutions of the newly obtained HFCP‐substituted helicenes are also described. [ABSTRACT FROM AUTHOR]

A highly enantioselective synthesis of 1,12‐disubstituted [4]carbohelicenes is reported. The key step for the developed synthetic route is a Au‐catalyzed intramolecular alkyne hydroarylation, which is achieved with good to excellent regio‐ and enantioselectivity by employing TADDOL‐derived (TADDOL=α,α,α,α‐tetraaryl‐1,3‐dioxolane‐4,5‐dimethanol) α‐cationic phosphonites as ancillary ligands. Moreover, an appropriate design of the substrate makes the assembly of [4]helicenes of different substitution patterns possible, thus demonstrating the synthetic utility of the method. The absolute stereochemistry of the newly prepared structures was determined by X‐ray crystallography and characterization of their photophysical properties is also reported. [ABSTRACT FROM AUTHOR]

Three unprecedented helical nanographenes (1, 2, and 3) containing an azulene unit are synthesized. The resultant helical structures are unambiguously confirmed by X‐ray crystallographic analysis. The embedded azulene unit in 2 possesses a record‐high twisting degree (16.1°) as a result of the contiguous steric repulsion at the helical inner rim. Structural analysis in combination with theoretical calculations reveals that these helical nanographenes manifest a global aromatic structure, while the inner azulene unit exhibits weak antiaromatic character. Furthermore, UV/Vis‐spectral measurements reveal that superhelicenes 2 and 3 possess narrow energy gaps (2: 1.88 eV; 3: 2.03 eV), as corroborated by cyclic voltammetry and supported by density functional theory (DFT) calculations. The stable oxidized and reduced states of 2 and 3 are characterized by in‐situ EPR/Vis–NIR spectroelectrochemistry. Our study provides a novel synthetic strategy for helical nanographenes containing azulene units as well as their associated structures and physical properties. [ABSTRACT FROM AUTHOR]

A unified low‐temperature reaction mechanism on the formation of acenes, phenacenes, and helicenes—polycyclic aromatic hydrocarbons (PAHs) that are distinct via the linear, zigzag, and ortho‐condensed arrangements of fused benzene rings—is revealed. This mechanism is mediated through a barrierless, vinylacetylene mediated gas‐phase chemistry utilizing tetracene, [4]phenacene, and [4]helicene as benchmarks contesting established ideas that molecular mass growth processes to PAHs transpire at elevated temperatures. This mechanism opens up an isomer‐selective route to aromatic structures involving submerged reaction barriers, resonantly stabilized free‐radical intermediates, and systematic ring annulation potentially yielding molecular wires along with racemic mixtures of helicenes in deep space. Connecting helicene templates to the Origins of Life ultimately changes our hypothesis on interstellar carbon chemistry. [ABSTRACT FROM AUTHOR]

The influence of molecular vibrations on circularly polarized luminescence (CPL) in double helicenes DPC and DNH is reported by Tadashi Mori in a Research Article (e202319702). Specifically, in DPC (structure depicted in the picture), the study clarifies how structural changes during electronic transitions shape CPL spectra and dissymmetry (g) factor values, and it underscores the noteworthy contribution of Herzberg–Teller effects in enhancing CPL responses...By Tadashi MoriReported by Author [Extracted from the article]

Chiral organic fluorescent molecules with circularly polarized luminescence (CPL) properties have attracted much attention for their potential applications in chiral optical and electronic devices. Benzo [ ghi ]perylene is one of the classical polycyclic aromatic hydrocarbons (PAHs) with good fluorescent properties and has many applications in the fields including optoelectronic devices and fluorescence probes. In this work, chiral benzo [ ghi ]perylene substituted [n]helicenes were directly obtained from chiral BINOL. The introduction of benzo [ ghi ]perylene structure greatly improved the fluorescent efficiency of the pristine helicene molecules. These benzo [ ghi ]perylene substituted [n]helicenes show strong blue fluorescent emission in organic solutions with good fluorescent quantum yields. These molecules could also exhibit moderate fluorescent emission in the solid-states. Based on the DFT calculations results, the HOMOs and LUMOs of these molecules are mainly contributed by benzo [ ghi ]perylene, which forms an orthogonal geometry with helicene moieties. The enantiomers of these molecules show opposite signals in CD and CPL spectra. The g abs and g lum values could be increased with elongation of helicene structure. Compounds with [7]helicene moiety show relatively large g abs and g lum values, which could reach up to 3.6 × 10−3 and 1.0 × 10−3, respectively. This work has provided a new strategy to develop chiral organic emitters through integration of benzo [ ghi ]perylene and helicene structures, which exhibit efficient fluorescent emission and intense CPL properties. [Display omitted] • Chiral benzo [ ghi ]perylene substituted [n]helicenes have been synthesized. • These molecules display strong blue fluorescent emission in solutions. • These molecules show strong Cotton effect in CD spectra with good g abs values. • Benzo [ ghi ]perylene substituted [6]helicenes exhibits intense CPL properties. [ABSTRACT FROM AUTHOR]

Organic semiconductors hold the promise of simple, large area solution deposition, low thermal budgets as well as compatibility with flexible substrates, thus emerging as viable alternatives for cost-effective (opto)-electronic devices. In this study, we report the optimized synthesis and characterization of a helically shaped polycyclic aromatic compound, namely benzo[i]pentahelicene-3,6-dione, and explored its use in the fabrication of organic field effect transistors. In addition, we investigated its thermal, optical absorption, and electrochemical properties. Finally, the single crystal X-ray characterization is reported.

In the corrected theoretical spectrum, the experimental finding is reproduced in the sense that the G-mode band has a slightly higher intensity than the D-mode band. In the original theoretical spectrum (incident laser wavelength I i = 540 nm), the G-mode band was predicted to be of weaker intensity than the D-mode band, in contradiction to the experimental finding. We previously reported calculations of the Raman optical activity (ROA) spectrum of an iron-alkynyl-helicene complex (labeled B 2a b in the original article). [Extracted from the article]

The effective combination of chirality and magnetism in a single crystalline material can lead to fascinating cross-effects, such as magneto-chiral dichroism. Among a large variety of chiral ligands utilized in the design and synthesis of chiral magnetic materials, helicenes seem to be the most appealing ones, due to the exceptionally high specific rotation values that reach thousands of deg·cm3·g−1·dm−1, which is two orders of magnitude higher than for compounds with chiral carbon atoms. Despite the sizeable family of transition metal complexes with helicene-type ligands, there are only a few examples of such complexes with lanthanide ions. In this mini-review, we describe the most recent developments in the field of lanthanide-based complexes with helicene-type ligands and summarize insights regarding the further exploration of this family of compounds towards multifunctional chiral lanthanide single molecule magnets (Ln-SMMs).