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Comprehensive Summary: As a class of organic dyes, boron‐containing compounds play an important role in organic luminescent materials. They have attracted considerable attention due to their unique photophysical properties. Chiral luminescent systems have a wide range of practical applications in biological imaging, optoelectronic devices, information storage and 3D display. Boron‐containing chiral luminescent materials can not only effectively improve the luminescent properties of CPL materials, but also bring unique properties to the system, which enables them to be used as favorable CPL emitting materials for an expanded range of applications. Here, we review the research progress of boron‐containing chiral luminescent materials by the detailed discuss according to different chiral skeletons, such as point chirality, 1,1'‐binaphthyl, [n]helicenes, [2,2]paracyclophane and pillar[5]arenes. We believe that this review is of significance for the development of boron‐containing compounds and CPL materials. Key Scientists: The studies of circularly polarized luminescence (CPL) based on small organic molecules have advanced significantly. However, boron‐containing chiral luminescent materials have gained attention only in recent years. In 2019, Zhao's group prepared a binaphthalene derivative modified with triarylborane, representing the organic small molecule luminescent material to exhibit CPL characteristics responsive to both solvent and fluoride ions. In 2020, the Chen's group used the unique luminescence properties and steric effects of triarylborane and triphenylamine to prepare CPL materials based on the planar chiral pillar[5]arenes. In 2021, Wang's group developed a new class of B,N‐embedded double hetero[7]helicenes molecules that exhibit strong chiroptical responses in the UV‐visible region. In the same year, He's group used asymmetric reactions to synthesize boron‐based point‐chirality compounds with high efficiency and enantioselectivity. In 2023, Ravat synthesized 1,4‐B,N‐embedded helicenes exhibiting narrow‐band fluorescence and CPL. During this period, Matthias Wagner et al obtained (BO)2‐doped tetrathia[7]helicene via an efficient four‐step synthesis, and Zheng reported the nearly pure green circularly polarized electroluminescent device (CP‐OLED). In 2024, Chen's group prepared B,N‐embedded hetero‐[9]helicenes offering a pathway towards significantly enhanced efficiency in helicene‐based CPEL. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: As a class of organic dyes, boron‐containing compounds play an important role in organic luminescent materials. They have attracted considerable attention due to their unique photophysical properties. Chiral luminescent systems have a wide range of practical applications in biological imaging, optoelectronic devices, information storage and 3D display. Boron‐containing chiral luminescent materials can not only effectively improve the luminescent properties of CPL materials, but also bring unique properties to the system, which enables them to be used as favorable CPL emitting materials for an expanded range of applications. Here, we review the research progress of boron‐containing chiral luminescent materials by the detailed discuss according to different chiral skeletons, such as point chirality, 1,1'‐binaphthyl, [n]helicenes, [2,2]paracyclophane and pillar[5]arenes. We believe that this review is of significance for the development of boron‐containing compounds and CPL materials. Key Scientists: The studies of circularly polarized luminescence (CPL) based on small organic molecules have advanced significantly. However, boron‐containing chiral luminescent materials have gained attention only in recent years. In 2019, Zhao's group prepared a binaphthalene derivative modified with triarylborane, representing the organic small molecule luminescent material to exhibit CPL characteristics responsive to both solvent and fluoride ions. In 2020, the Chen's group used the unique luminescence properties and steric effects of triarylborane and triphenylamine to prepare CPL materials based on the planar chiral pillar[5]arenes. In 2021, Wang's group developed a new class of B,N‐embedded double hetero[7]helicenes molecules that exhibit strong chiroptical responses in the UV‐visible region. In the same year, He's group used asymmetric reactions to synthesize boron‐based point‐chirality compounds with high efficiency and enantioselectivity. In 2023, Ravat synthesized 1,4‐B,N‐embedded helicenes exhibiting narrow‐band fluorescence and CPL. During this period, Matthias Wagner et al obtained (BO)2‐doped tetrathia[7]helicene via an efficient four‐step synthesis, and Zheng reported the nearly pure green circularly polarized electroluminescent device (CP‐OLED). In 2024, Chen's group prepared B,N‐embedded hetero‐[9]helicenes offering a pathway towards significantly enhanced efficiency in helicene‐based CPEL. [ABSTRACT FROM AUTHOR]

Photocyclization of 8-aryloxy-3-phenylbenzo[e][1,2,4]triazines leads to π-delocalized helicene radicals 1[n] (n = 5, 6, 7) containing the ring-fused 1,4-dihydro[1,2,4]triazin-4-yl as a spin source. Single crystal XRD revealed that the photocyclization to 1[n] involves a Smiles rearrangement. Radicals 1[n] were investigated by spectroscopic, electrochemical and DFT methods, while racemic helicene 1[7] was resolved and ECD spectra were recorded. [ABSTRACT FROM AUTHOR]

Despite recent tremendous progress in the synthesis of nonplanar chiral aromatics, and helicenes in particular, their conversion to half‐sandwich or sandwich transition metal complexes still lags behind, although they represent an attractive family of modular and underexplored chiral architectures with a potential catalytic use. In this work, starting from various chiral helicene‐indene proligands, we prepared the enantio‐ and diastereopure oxa[6]‐ and oxa[7]helicene‐indenido half‐sandwich RhI and RhIII complexes and oxa[7]helicene‐bisindenido ansa‐metallocene FeII complex. To document their use, oxahelicene‐indenido half‐sandwich RhIII complexes were employed as chiral catalysts in enantioselective C−H arylation of benzo[h]quinolines with 1‐diazonaphthoquinones to afford a series of axially chiral biaryls in mostly good to high yields and in up to 96 : 4 er. Thus, we developed stereocontrolled synthesis of chiral helicene‐indenido ansa‐ and half‐sandwich metal complexes, successfully demonstrated the first use of such helicene Cp‐related metal complexes in enantioselective catalysis, and described an unusual sequence of efficient central‐to‐helical‐to‐planar‐to‐axial chirality transfer. [ABSTRACT FROM AUTHOR]

Panchromatic dyes have been highly useful in the realm of optical devices. Here, we report that panchromatic dyes with heterohelicenes have been successfully synthesized using a donor‐acceptor strategy. Our synthesis resulted in the creation of π‐extended aza[5]helicene oligomers with butadiyne linkages, which displayed bathochromically shifted absorption and emission spectra. The solvent‐dependent optical measurements revealed the intramolecular charge transfer characteristic of these molecules, and theoretical calculations described the biased molecular orbitals on the azahelicene units that generated the charge‐transfer characteristic. Encouraged by these results, we also prepared donor‐acceptor‐donor dyads using azahelicenes and dimide derivatives, resulting in panchromatic absorbing characteristics covering the range from 250 nm to 800 nm. Theoretical calculations showed the presence of mixed charge‐transfer transitions and localized transitions on the azahelicene units, which led to a broad light‐absorbing property covering the near IR region. Additionally, we conducted measurements of circular dichroism and circularly polarized luminescence for the obtained products. The g‐values were reduced by oligomerization, indicating that the lowest energy transitions were allowed in nature. [ABSTRACT FROM AUTHOR]

Helicenes and helicenoid structures are promising candidates for future applications exploiting circularly polarized light. Ideal candidates should possess near‐quantitative photoluminescence quantum yield, a high luminescence dissymmetry factor and an adjustable HOMO‐LUMO gap. However, carbo[n]helicenes are poorly luminescent compounds and they absorb light mainly in the ultraviolet region. Here we show that the incorporation of a carbonyl group into helical scaffold significantly improves the fluorescence quantum yield and shifts the absorption to visible region. Although the carbonyl group is commonly considered as detrimental to efficient emission, fluorescence quantum yields up to Φ=0.43 were recorded. A straightforward synthetic approach to a highly luminescent tetraceno[6]helicenone and an aza analogue has been developed. The key step is a radical cyclization which is achieving dehydrative π‐extension. The aza‐analogue was incorporated as an emitter in organic light emitting diodes (OLEDs) and showed good performance. [ABSTRACT FROM AUTHOR]

Helicenes and their derivatives show great application prospects as circularly polarized luminescence (CPL) materials, but their fluorescence quantum yields (ΦFLs) need a breakthrough urgently. Herein, we reported a series of D‐π‐A type helical luminescent emitters by combining the [7]helicene‐like imide acceptor with five different donors. The obtained five emitters display blue‐to‐orange luminescence and markedly enhanced ΦFL. Notably, TPA‐NiBTI exhibits the maximum ΦFL in solution, while TPE‐NiBTI achieves a maximum ΦFL in the solid state. Their two pairs of enantiomers, (P/M)‐TPA‐NiBTI and (P/M)‐TPE‐NiBTI, exhibit remarkable CPL activities, and their doped PS film both displayed doubled ΦFLs. Among them, [(P/M)‐TPE‐NiBTI]‐doped PS film exhibits the maximum luminescence dissymmetry factor (|glum|) value of 9.0×10−4 and the maximum ΦFL of 22 %. This molecular design strategy presents a promising approach to improving the ΦFL of helicene derivatives, thereby facilitating their potential application into chiral optoelectronic devices. [ABSTRACT FROM AUTHOR]

Circularly polarized luminescence (CPL) from chiral molecules is attracting much attention due to its potential use in optical materials. However, formulation of CPL emitters as molecular solids typically deteriorates photophysical properties in the aggregated state leading to quenching and unpredictable changes in CPL behavior impeding materials development. To circumvent these shortcomings, a supramolecular approach can be used to isolate cationic dyes in a lattice of cyanostar‐anion complexes that suppress aggregation‐caused quenching and which we hypothesize can preserve the synthetically‐crafted chiroptical properties. Herein, we verify that supramolecular assembly of small‐molecule ionic isolation lattices (SMILES) allows translation of molecular ECD and CPL properties to solids. A series of cationic helicenes that display increasing chiroptical response is investigated. Crystal structures of three different packing motifs all show spatial isolation of dyes by the anion complexes. We observe the photophysical and chiroptical properties of all helicenes are seamlessly translated to water soluble nanoparticles by the SMILES method. Also, a DMQA helicene is used as FRET acceptor in SMILES nanoparticles of intensely absorbing rhodamine antennae to generate an 18‐fold boost in CPL brightness. These features offer promise for reliably accessing bright materials with programmable CPL properties. [ABSTRACT FROM AUTHOR]

Thiahelicenes, an important subclass of helicenes, are renowned for their pronounced chiroptical properties, particularly circular dichroism. However, the exploration of their circularly polarized luminescence (CPL) has been hindered due to their inherently weak fluorescence, leaving a critical gap in the development of thiahelicenes as efficient CPL emitters. To address this limitation, a novel strategy for enhancing the luminescence of thiahelicenes by integrating thiophene‐containing units with a highly emissive hexabenzoperylene (HBP) core is presented. Two isomeric HBP‐cored double thiahelicenes are synthesized, which serve as proof of concept. These molecules exhibit exceptionally high fluorescence quantum yields (ΦF = 83% and 91%), surpassing all previously reported thiahelicenes. Furthermore, their luminescence dissymmetry factors show a four‐fold enhancement compared to the parent HBP, resulting in a remarkable CPL brightness of up to 84.9 M−1 cm−1. These findings not only address the fluorescence limitation of thiahelicenes but also establish a new pathway for developing high‐performance CPL materials. [ABSTRACT FROM AUTHOR]

The relationship between chemical structure and chiroptical properties is not always clearly understood. Nowadays, efforts to develop new systems with enhanced optical properties follow the trial‐error method. A large number of data would allow us to obtain more robust conclusions and guide research toward molecules with practical applications. In this sense, in this work we predict the chiroptical properties of millions of halogenated [6]helicenes in terms of the rotatory strength (R). We have used DFT calculations to randomly create derivatives including from 1 to 16 halogen atoms, that were then used as a data set to train different deep neural network models. These models allow us to i) predict the Rmax for any halogenated [6]helicene with a very low computational cost, and ii) to understand the physical reasons that favour some substitutions over others. Finally, we synthesized derivatives with higher predicted Rmax obtaining excellent correlation among the values obtained experimentally and the predicted ones. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Construction of helicenes by inducing heteroatoms has regarded as an effective strategy to enhance the chiroptical properties. We report a facile synthesis of a multiple helicene based on four indoles with two electron‐rich NBN‐coved edges. The structure of the NBN‐coved multiple helicene was confirmed by single‐crystal X‐ray diffraction analysis, revealing a twisted double [5]helicene motif with a saddle‐shaped skeleton. This NBN‐coved helicene showed strong green fluorescence with good photoluminescence quantum yield. Both theoretical calculations and experimental investigation have been exploited to probe the impact of electron‐rich NBN units on aromaticity and photophysical properties of the helicene. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Construction of helicenes by inducing heteroatoms has regarded as an effective strategy to enhance the chiroptical properties. We report a facile synthesis of a multiple helicene based on four indoles with two electron‐rich NBN‐coved edges. The structure of the NBN‐coved multiple helicene was confirmed by single‐crystal X‐ray diffraction analysis, revealing a twisted double [5]helicene motif with a saddle‐shaped skeleton. This NBN‐coved helicene showed strong green fluorescence with good photoluminescence quantum yield. Both theoretical calculations and experimental investigation have been exploited to probe the impact of electron‐rich NBN units on aromaticity and photophysical properties of the helicene. [ABSTRACT FROM AUTHOR]

A twisted chiral nanographene (NG) surrounded by eight bulky tert‐butyl groups fused with emissive chromophore perylene was synthesized by highly regioselective cyclodehydrogenation strategy in which a double [6]helicene was formed simultaneously. The twisted 4‐meso was unambiguously confirmed by single crystal X‐ray analysis. The NG showed an excellent photoluminescence quantum yield (ϕf) of 55 %, indicating its great potential for chiral optoelectronics. [ABSTRACT FROM AUTHOR]

A novel hybrid nanocarbon consisting of one rippled and two planar nanosheets has been synthesized and characterized. Two meso pairs of [5]helicenes are formed along the long molecular axis of the hybrid to connect rippled and planar subunits, leading to a stable conformation. It is shown that the hybrid possesses the individual electronic properties of the rippled and planar subunits. Compared to the rippled subunit, such hybrid has a better geometric match to C60 and complexes with C60 in a 1 : 1 stoichiometry, with the association constant on the order of 105 M−1. The hybrid displays unusual anti‐Kasha fluorescence emission. The transient absorption spectroscopy revealed that the singlet fission (SF) from higher level singlet excited states (Sn) is operative in the film of the hybrid. [ABSTRACT FROM AUTHOR]

The synthesis and stabilization of heteroatom‐doped nanocarbon molecules, such as carbazole‐containing (super)helicenes, present significant challenges due to the complexities involved in maintaining structural integrity and electronic functionality. In this study, we successfully synthesized a carbazole‐centered expanded tris‐hexabenzo[7]helicene (1) via a facile FeCl3‐mediated Scholl coupling reaction. 1 exhibits both chemical and chiral stability and demonstrates fluorescence at 628 nm with a quantum yield of 0.40. Additionally, the enantiomers of 1 display pronounced chiroptical properties, including a distinct circular dichroism (CD) signal spanning from 300 to 600 nm. The absorption dissymmetry factor (|gabs|) is determined to be 2.98×10−3, while the circularly polarized luminescence brightness (BCPL) is measured as 32.50 M−1 cm−1. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Carbohelicenes have garnered considerable attention for their inherent chirality and structural flexibility. Increasing multi‐helicity and incorporating non‐six‐membered rings to substitute benzenoid rings within helicenes are effective strategies for introducing unique photoelectric properties. Despite the disclosure of numerous helicenes, the inaccessible precursors and the lack of synthetic routes pose a challenge in achieving desired helicene structures fused with non‐benzenoid rings. Herein, we report the synthesis of multiple non‐benzenoid carbohelicenes fused with fluorene unit(s) through intramolecular cyclodehydrogenation of 9,10‐di(naphthalen‐1‐ yl)anthracene on Au(111) surface. Two potential cyclodehydrogenation manners between naphthyl and anthracene lead to the formation of fluorene‐fused [5]helicene and [4]helicene moiety. Consequently, a total of four stable products were observed. The atomic topographies of products are characterized by bond‐resolving scanning tunneling microscopy. The chiral helicity of targeted products can be switched by tip manipulation. Density‐functional‐theory calculations unveils the reaction pathway of four products. The comparative analysis of their respective energy barriers exhibits a correlation with the experimentally determined yields. Furthermore, we synthesize the polymer chains incorporating non‐benzenoid carbohelicenes via the Ullmann reaction of 2,6‐dibromo‐9,10‐di(1‐naphthyl)anthracene precursors. Our work proposes a synthetic methodology for several novel helicene‐like structures fused with fluorene units and the polymer bearing helicene subunits, thus highlighting the immense potential of these compounds in the application fields of luminescent electronic devices. [ABSTRACT FROM AUTHOR]

Doping of polycyclic conjugated hydrocarbons (PCHs) with sulfur atoms is becoming more and more important as a means of creating unique functional materials. Recently, thiophene‐containing multiple helicenes have garnered enormous attention due to their intriguing electronic and (chir)optical properties compared with carbohelicenes. However, the efficient synthesis of thiopyran‐containing multiple helicenes and the underlying sulfur doping mechanisms are rather unexplored. Herein, the synthesis and structural analysis of a thiopyran‐containing double [7]helicene 3 are reported. X‐ray crystallographic analysis reveals 3 and its dication with C2‐symmetric propeller‐shape structures and compact interactions in the solid state. 3 exhibits deep‐red to near‐infrared (NIR) fluorescence emission. Tunable aromaticity of the central benzene ring and thiopyran rings is found by chemical oxidation, which is further confirmed by nucleus‐independent chemical shift (NICS), anisotropy of the induced current density (ACID) and harmonic oscillator model of aromaticity (HOMA) analysis. Furthermore, the chiral and photosensitizing characters of 3 are investigated. The excellent deep‐red to NIR fluorescence, circularly polarized luminescence (CPL) and photosensitizing activities suggest that 3 can be used as an outstanding photosensitizer in photodynamic therapy (PDT) and bioimaging, especially paving the way for future CPL‐PDT and CPL‐bio‐probe applications. [ABSTRACT FROM AUTHOR]

Helicenes represent a class of fascinating π compounds with fused yet folded backbones. Despite their broad structural diversity, harnessing helicenes to develop well‐defined materials is still a formidable challenge. Here we report the synthesis of crystalline porous helicene materials by exploring helicenes to synthesize covalent 2D lattices and layered π frameworks. Topology‐directed polymerization of [6]helicenes and porphyrin creates 2D covalent networks with alternate helicene‐porphyrin alignment along the x and y directions at a 1.5‐nm interval and develops [6]helicene frameworks through reversed anti‐AA stack along the z direction to form segregated [6]helicene and porphyrin columnar π arrays. Notably, this π configuration enables the frameworks to be highly red luminescent with benchmark quantum yields. The [6]helicene frameworks trigger effieicnt intra‐framework singlet‐to‐singlet state energy transfer from [6]helicene to porphyrin and facilitate intermolecular triplet‐to‐triplet state energy transfer from frameworks to molecular oxygen to produce reactive oxygen species, harvesting a wide range of photons from ultraviolet to near‐infrared regions for light emitting and photo‐to‐chemical conversion. This study introduces a new family of extended frameworks, laying the groundwork for exploring well‐defined helicene materials with unprecedented structures and functions. [ABSTRACT FROM AUTHOR]

Chiral helicenes are widely used in fields related to organic materials and molecular machines relevant molecules, as well as serving as privileged frameworks for chiral ligands and catalysts. Therefore, the research into asymmetric routes for the synthesis of chiral helical compounds has garnered significant interest in recent years. In this regard, chirality conversion/transfer from chiral precursors has emerged as a powerful strategy for the construction of chiral helicenes, allowing the synthesis of various types of chiral helical compounds. This strategy has become and will remain a prominent research topic in the field of asymmetric synthesis. In this review article, described between 2012 and 2024, the approaches for the synthesis of chiral helicenes by chirality conversion or transfer from centrally chiral precursors are summarized. [ABSTRACT FROM AUTHOR]

Multi‐resonant thermally activated delayed fluorescence (MR‐TADF) helicenes show great potential as chiral emitters due to their typically high photoluminescence quantum yield and that they emit circularly polarized luminescence. Here, a new propeller‐shaped chiral MR‐TADF helicene DiKTa3, integrating three DiKTa moieties, was designed and synthesized aiming to achieve co‐parallel electronic and magnitude transition dipole moments that would lead to a high dissymmetry factor, g. It emits at λPL of 491 nm, with a full width at half maximum of 52 nm and has a moderate ΔEST value of 0.24 eV in toluene. The separated (P,P,P) enantiomer shows an absorption dissymmetry factor |gabs| of 6.8×10−4 at 450 nm, which results from a lower symmetry conformation adopted by the compound in solution than the C3‐symmetric optimized structure. This work highlights the strong influence that geometry can have on the chiroptical properties of the emitter. [ABSTRACT FROM AUTHOR]

The inherent helical chirality and improved π-stacking capabilities endow helicenes with fascinating photophysical characteristics when decorated with lateral π-extensions. Here, we report the synthesis and physicochemical characterization of expanded hetero[6]helicenes fused with thiadiazole and selenadiazole rings at the helical ends. Comparing these heterohelicenes revealed the impact of the heteroatom-embedded aromatic rings on the excited state and redox features. A small structural variation of the terminal rings from thiadiazole to selenadiazole caused a striking change in the heterohelical nanographenes. [ABSTRACT FROM AUTHOR]

The introduction of precise pore defects into nanocarbon structures results in the emergence of distinct physicochemical characteristics. However, there is a lack of research on non‐planar chiral nanographene involving precise pore defects. Herein, we have developed two analogues to the π‐extended pentadecabenzo[9]helicene (EP9H) containing embedded pore defects. Each molecules, namely extended dodecabenzo[7]helicene (ED7H; 1) or extended nonabenzo[5]helicene (EN5H; 2), exhibits dual‐state emission. Significantly, the value of |glum| of 1 is exceptionally high at 1.41×10−2 in solution and BCPL as 254 M−1 cm−1. In PMMA film, |glum| of 1 is 8.56×10−3, and in powder film, it is 5.00×10−3. This study demonstrates that nanocarbon molecules with pore defects exhibit dual‐state emission properties while maintaining quite good chiral luminescence properties. It was distinguished from the aggregation‐caused quenching (ACQ) effect corresponding to the nanocarbon without embedded defect. Incorporating pore defects into chiral nanocarbon molecules also simplifies the synthesis process and enhances the solubility of the resulting product. These findings suggest that the introduction of pore defects can be a viable approach to improve nanocarbon molecules. [ABSTRACT FROM AUTHOR]

Helicenes, with their unique helical structures, have long captured the interest of synthetic chemists, not only as end products, but also as versatile platforms for further chemical transformations. However, transforming [6]helicene into planar coronene typically requires harsh conditions and poses significant challenges. Herein, we demonstrate that replacing the terminal benzene ring of [6]helicene with a thiophene ring enables its photochemical transformation into coronene. Sulfur oxidation of the thiophene ring enables the corresponding thermal transformation, and the terminal tetrafluorination of the opposite benzene ring further accelerates this process, yielding 1,2‐difluorocoronene, as confirmed by X‐ray crystallography. The transformation begins with an intramolecular Diels–Alder reaction, whose activation energy is significantly lowered by these structural changes. Our findings underscore the utility of strategic modifications such as sulfur oxidation and fluorination in promoting this "helix‐to‐disc" conversion and opening new avenues for synthesizing functional polycyclic aromatics. [ABSTRACT FROM AUTHOR]

The present article provides a personalized account on CH-arylation reactions employed for the synthesis of heterocycles. The presence of a nitro group allowed for direct and regioselective CH-arylations of pyrazoles, imidazoles, indoles and a variety of purine analogues. Direct CH-arylations without the presence of an activating nitro-group were employed for inter- and intramolecular reactions of purine derivatives, which allowed for the synthesis of a great variety of polycyclic systems. Domino C–N coupling / hydroamination / CH-activation reactions of diarylacetylenes with anilines allowed for the synthesis of polycondensated N -heterocycles. Products include indolo- and azaindolo[1,2- f ]phenanthridines, quinolino[3′,4′:4,5]pyrrolo[1,2- f ]phenanthridines, pyrimido[5′,4′:4,5]pyrrolo[1,2- f ]phenanthridines, and benzothieno[2′,3′:4,5]pyrrolo[1,2- f ]phenanthridines. The reaction of N -heterocycles, such as indoles, with 1,1-difluoroalkenes resulted in a twofold addition-elimination reaction to give 1,1-diaminoalkenes, which were transformed by CH-arylation into various polycondensated heterocycles, such as indoloisoquinolines, thienoindolizines, oxepines and helicenes. Pyridofluoranthenes, diindenopyrene and azadiindenopyrenes were prepared by a combination of Pd-catalyzed cross-coupling reactions with acid-mediated cycloisomerizations and Pd-catalyzed intramolecular CH-arylations. Bis(carbazoles), benzodithiazoles, benzodithiophenes and 2,5-diarylpyrroles were prepared by inter- and intramolecular CH-arylation reactions. [ABSTRACT FROM AUTHOR]

Double helicenes, with their notable chirality and intriguing properties, have captivated the great interest of chemists. Comprehending the relationship between their structure and properties is fundamentally significant for enhancing performance and facilitating practical applications. In this study, we have explored the photophysical properties of a series of double helicenes, composed of two perylene diimides (PDIs) entwined via C–C single bonds, using density functional theory (DFT) calculations. These properties include electronic transition characteristics, absorption spectra, and second-order nonlinear optical (NLO) responses. The simulated electronic absorption spectra of the parent compound (compound 1) closely resemble the experimental results. Compound 1 also exhibits an intrinsic second-order NLO response. Compounds 2–7, designed by substituting the terminal CH3 groups in compound 1 with electron acceptors (NO2, 7,7,8,8-tetracyanoquinodimethane (TCNQ)), electron donors (NH2, tetrathiafulvalene (TTF)), and their combinations, demonstrate tunable HOMO/LUMO distributions, band gaps, absorption intensities, and electron transition properties. Notably, the maximum βHRS value reaches 8.71 × 10−30 esu, approximately 95 times greater than that of the organic molecule urea. Our findings provide insights for the development of double helicenes with PDI subunits. [ABSTRACT FROM AUTHOR]

Molecules with a π-system that can be mapped onto a Möbius strip may display Möbius aromaticity. Such molecules are difficult to synthesize because they have a twisted structure. Recently, we combined chiral [6]helicene and fluorescent [7]cycloparaphenylene, and synthesized the first helicene para -phenylene ([6,7]HPP) carbon nanohoop. We have demonstrated that this design strategy ultimately provides a Möbius topology of the molecular π-electron system and, therefore, offers the potential to study Möbius aromaticity experimentally. In addition, the synthesized nanohoop exists as a mixture of conformers in solution. Some of the conformers possess a different orientability of their π-systems, i.e., they differ in their topology. As a result, the recorded circularly polarized luminescence of isolated enantiomers displays both left- and right-handedness of the emitted light, each emanating from a conformer with a different π-system topology. Therefore, [6,7]HPP provided the first experimental evidence of such topological bistability in carbon nanohoops. [ABSTRACT FROM AUTHOR]

Boron‐doped helicenes, known for their unique electronic and photophysical properties, are of great interest for numerous applications. This research introduces two new azabora[6]helicenes, H[6]BN1 and H[6]BN2, synthesized through an efficient method. These molecules have boron and nitrogen atoms in opposing positions, enhancing their distinctive attributes. Both helicenes show excellent emission properties, with H[6]BN1 and H[6]BN2 exhibiting narrowband blue fluorescence and circularly polarized luminescence (CPL), achieving glum values of 4~5×10−4 which is beneficial for chiroptical applications. The addition of a donor group, 3, 6‐di‐tert‐butyl‐9H‐carbazole, in H[6]BN2 improves luminescence, likely due to enhanced molecular orbital overlap and electron delocalization. H[6]BN1′s needle‐like single crystals exhibit mechanochromism, changing luminescent color from yellow to green under mechanical stress, which is promising for stimulus‐responsive materials. In conclusion, this study presents a novel class of BN[6]helicenes with superior chiroptical properties. Their combination of electronic features and mechanochromism makes them ideal for advanced chiroptical materials, expanding the potential of helicene‐based compounds and offering new directions for the synthesis of molecules with specific chiroptical characteristics. [ABSTRACT FROM AUTHOR]

A triskelion‐shaped triradical triindeno[1,2‐a:1′,2′‐g : 1′′,2′′‐m]triphenylen‐7‐yl (1) and its internally fused derivative (2) obtained by oxidative cyclization were prepared in a straightforward synthetic sequence. Both compounds were confirmed to be triradicals and to possess intramolecular antiferromagnetic exchange interactions between spins, displaying a spin‐frustrated doublet ground state with doublet‐quartet energy gaps of −0.14 kcal/mol for 1 and −0.06 kcal/mol for 2. Despite their open‐shell character, they were sufficiently stable to be handled under ambient conditions on a timescale of days. Both compounds could be reversibly reduced to mono‐, di‐, and trianions and oxidized to 1+ and 22+, with strong NIR absorptions (1800 to over 3200 nm) observed for all open‐shell ions. [ABSTRACT FROM AUTHOR]

Synthetic options for conversion of indeno[2,1‐c]fluorene‐5,8‐diones into larger polyaromatic compounds with extended π‐conjugated systems were explored. The crucial two‐fold transformation of the five‐membered ketone moieties of indeno[2,1‐c]fluorene‐5,8‐diones was based either on a one‐carbon homologation or on a ring‐expansion reaction which eventually enabled syntheses of compounds possessing substituted tribenzo[a,e,l]indeno[1,2,3‐hi]acephenanthrylenes and [5]helicenes scaffolds. The former was prepared by using a reaction sequence based on Ramirez olefination, intramolecular Heck reaction, and intermolecular Suzuki‐Miyaura cross‐coupling, whereas the latter utilized a sequence comprising Büchner−Curtius−Schlotterbeck reaction and intermolecular Suzuki‐Miyaura cross‐coupling. Scholl reaction of selected [5]helicenes yielded planarized polyaromatic compounds with the tribenzo[a,e,l]indeno[1,2,3‐hi]acephenanthrylene scaffold. Where possible, structures of products were confirmed by X‐ray diffraction analyses. Photophysical properties were determined as well. [ABSTRACT FROM AUTHOR]

The spatial magnetic properties (through‐space NMR shieldings—TSNMRSs—actually the ring current effect in 1H NMR spectroscopy) of the recently synthesized infinitene (the helically twisted [12]circulene) have been calculated using the GIAO perturbation method employing the nucleus‐independent chemical shift (NICS) concept and visualized as iso‐chemical‐shielding surfaces (ICSS) of various size and direction. Both 1H and 13C chemical shifts of infinitene and the aromaticity of this esthetically very appealing molecule have been studied subject to the ring current effect thus obtained. This spatial magnetic response property of TSNMRSs dominates the different magnitude of 1H and 13C chemical shifts, especially in the cross‐over section of infinitene, which is unequivocally classified as an aromatic molecule based on the deshielding belt of its ring current effect. Differences in aromaticity of infinitene compared with isolated benzene can also be qualified and quantified on the magnetic criterion. [ABSTRACT FROM AUTHOR]

Nanographenes are of increasing importance owing to their potential applications in the photoelectronic field. Meanwhile, recent studies have primarily focused on the pure electronic spectra of nanographenes, which have been found to be inadequate for describing the experimental spectra that contain vibronic progressions. In this study, we focused on the vibronic effect on the electronic transition of a range of chiral nanographenes, especially in the low-energy regions with distinct vibronic progressions, using theoretical calculations. All the calculations were performed at the PBE0-D3(BJ)/def2-TZVP level of theory, adopting both time-dependent and time-independent approaches with Franck–Condon approximation. The resulting calculated curves exhibited good alignment with the experimental data. Notably, for the nanographenes incorporating helicene units, owing to the increasing π-extension, the major vibronic modes in the vibrationally resolved spectra differed significantly from those of the primitive helicenes. This investigation suggests that calculations that account for the vibronic effect could have better reproducibility compared with calculations based solely on pure electronic transitions. We anticipate that this study could pave the way for further investigations into optical and chiroptical properties, with a deeper understanding of the vibronic effect, thereby providing theoretical explanations with higher precision on more sophisticated nanographenes. [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. [ABSTRACT FROM AUTHOR]

The combination of different distortion motifs in nanographenes and polycyclic conjugated hydrocarbons has been the focus of significant attention during the last decade. The continual discovery of multiple carbon allotropes has fueled the field. A plethora of research groups around the globe are engaged in developing methods for the preparation of discrete graphene or fullerene fragments and new carbon allotropes. The goal is to fully understand the structure–property relationships in these systems. Herein, we present our journey and contributions to the field, from the development of a synthetic methodology towards functionalized heptagon-containing hexa- peri -hexabenzocoronenes through the preparation of saddle-helix hybrid nanographenes, the study of heptagon-containing cumulenic and open-shell systems, nanographenes embedded with higher order carbocycles, and the study of their electronic properties on-surface and by single-molecule conductance. 1 Introduction 2 The Finding of a Cornerstone Scaffold 3 Saddle-Helix Hybrid Nanographenes 4 Cumulenic and Diradicaloid Systems 5 Supramolecular Studies 6 Octagon- and Nonagon-Embedded Nanographenes 7 Molecular Electronics and On-Surface Studies 8 Outlook [ABSTRACT FROM AUTHOR]

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 glum factors of ≈1.7×10−3 at λem=525 nm, and also in the solid state, with glum factors of ≈1.2×10−3 in spite of the strong decrease of the quantum efficiency. [ABSTRACT FROM AUTHOR]

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 (BCPL) 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The incorporation of pentagon‐heptagon pairs into helical nanographenes lacks a facile synthetic route, and the impact of these pairs on chiroptical properties remains unclear. In this study, a method for the stepwise construction of pentagon‐heptagon pairs in helical nanographenes by the dehydrogenation of [6]helicene units was developed. Three helical nanographenes containing pentagon‐heptagon pairs were synthesized and characterized using this approach. A wide variation in the molecular geometries and photophysical properties of these helical nanographenes was observed, with changes in the helical length of these structures and the introduction of the pentagon‐heptagon pairs. The embedded pentagon‐heptagon pairs reduced the oxidation potential of the synthesized helical nanographenes. The high isomerization energy barriers enabled the chiral resolution of the helicene enantiomers. Chiroptical investigations revealed remarkably enhanced circularly polarized luminescence and luminescence dissymmetry factors with an increasing number of the pentagon‐heptagon pairs. [ABSTRACT FROM AUTHOR]

Helical nanographenes with high quantum yields and strong chiroptical responses are pivotal for developing circularly polarized luminescence (CPL) materials. Here, we present the successful synthesis of novel π‐extended double [7]helicenes (ED7Hs) where two helicene units are fused at the meta‐ or para‐position of the middle benzene ring, respectively, as the structural isomers of the reported ortho‐fused ED7H. The structural geometry of these ED7Hs is clearly characterized by single‐crystal X‐ray analysis. Notably, this class of ED7Hs exhibits bright luminescence with high quantum yields exceeding 40 %. Through geometric regulation of two embedded [7]helicene units from ortho‐, meta‐ to para‐position, these ED7Hs display exceptional amplification in chiroptical responses. This enhancement is evident in a remarkable approximate fivefold increase in the absorbance and luminescence dissymmetry factors (gabs and glum), respectively, along with a boosted CPL brightness up to 176 M−1 cm−1, surpassing the performance of most helicene‐based chiral NGs. Furthermore, DFT calculations elucidate that the geometric adjustment of two [7]helicene units allows the precise alignment of electric and magnetic transition dipole moments, leading to the observed enhancement of their chiroptical responses. This study offers an effective strategy for magnifying the CPL performance in chiral NGs, promoting their expanded application as CPL emitters. [ABSTRACT FROM AUTHOR]

The adjustment of the main helical scaffold in helicenes is a fundamental strategy for modulating their optical features, thereby enhancing their potential for diverse applications. This work explores the influence of helical elongation (n = 5–9) on the structural, photophysical, and chiroptical features of symmetric oxa[n]helicenes. Crystal structure analyses revealed structural variations with helical extension, impacting torsion angles, helical pitch, and packing arrangements. Through theoretical investigations using density functional theory (DFT) calculations, the impact of helical extension on aromaticity, planarity distortion, and heightened chiral stability were discussed. Photophysical features were studied through spectrophotometric analysis, with insights gained through time‐dependent DFT (TD‐DFT) calculations. Following optical resolution via chiral high‐performance liquid chromatography (HPLC), the chiroptical properties of both enantiomers of oxa[7]helicene and oxa[9]helicene were investigated. A slight variation in the main helical scaffold of oxa[n]helicenes from [7] to [9] induced an approximately three‐fold increase in dissymmetry factors with the biggest values of|glum| of oxa[9]helicene (2.2 × 10−3) compared to|glum|of oxa[7]helicene (0.8 × 10−3), findings discussed and supported by TD‐DFT calculations. [ABSTRACT FROM AUTHOR]

A benzannulated double aza[9]helicene 1 was successfully synthesized via a one‐pot oxidative fusion reaction. 1 was derivatized to N‐alkylated double aza[9]helicene 1‐Et and 1‐Bu, whose structures were determined by X‐ray diffraction analysis. 1‐Et and 1‐Bu exhibited red‐shifted absorption and fluorescence spectra compared to single aza[9]helicene. The double aza[9]helicenes were expected to have two different conformers. Consistent with solid‐state structure, the chiral‐isomer was estimated to be more stable by 16 kcal/mol relative to meso‐isomer. Indeed, enantiomers of 1‐Et and 1‐Bu were optically resolved by HPLC and showed mirror‐imaged CD and CPL spectra with the CPL brightness up to 19.2 M−1cm−1 for 1‐Bu. [ABSTRACT FROM AUTHOR]

Expanded azahelicenes, as heteroanalogues of helically chiral helicenes, hold significant potential for chiroptical materials. Nevertheless, their investigation and research have remained largely unexplored. Herein, we present the facile synthesis of a series of expanded azahelicenes NHn (n=1–5) consisting of 11, 19, 27, 35, and 43 fused rings, mainly by Suzuki coupling followed by Bi(OTf)3‐mediated cyclization of vinyl ethers. The structures of NH2, NH3 and NH4 were confirmed through X‐ray crystallography analysis, and their (P)‐ and (M)‐ enantiomers were also isolated with chiral high performance liquid chromatography. The enantiomers exhibit large absorption (abs) and luminescence (lum) dissymmetry factors, with |gabs|max=0.044; |glum|max=0.003 for NH2, |gabs|max=0.048; |glum|=0.014 for NH3, and |gabs|max=0.043; |glum|max=0.021 for NH4, which are superior to their respective all‐carbon analogues. [ABSTRACT FROM AUTHOR]

The intrinsic helical π‐conjugated skeleton makes helicenes highly promising for circularly polarized electroluminescence (CPEL). Generally, carbon helicenes undergo low external quantum efficiency (EQE), while the incorporation of a multi‐resonance thermally activated delayed fluorescence (MR‐TADF) BN structure has led to an improvement. However, the reported B,N‐embedded helicenes all show low electroluminescence dissymmetry factors (gEL), typically around 1×10−3. Therefore, the development of B,N‐embedded helicenes with both a high EQE and gEL value is crucial for achieving highly efficient CPEL. Herein, a facile approach to synthesize B,N‐embedded hetero[9]helicenes, BN[9]H, is presented. BN[9]H shows a bright photoluminescence with a maximum at 578 nm with a high luminescence dissymmetry factor (|glum|) up to 5.8×10−3, attributed to its inherited MR‐TADF property and intrinsic helical skeleton. Furthermore, circularly polarized OLED devices incorporating BN[9]H as an emitter show a maximum EQE of 35.5 %, a small full width at half‐maximum of 48 nm, and, more importantly, a high |gEL| value of 6.2×10−3. The Q‐factor (|EQE×gEL|) of CP‐OLEDs is determined to be 2.2×10−3, which is the highest among helicene analogues. This work provides a new approach for the synthesis of higher helicenes and paves a new way for the construction of highly efficient CPEL materials. [ABSTRACT FROM AUTHOR]

The circularly polarized luminescence (CPL) spectra of S‐ and X‐shaped double helicenes exhibit distinct vibrational structures and overall shape variations. In this study, we conducted an in‐depth investigation into the vibronic effects influencing the CPL spectra of two double helicenes, namely DPC and DNH. Employing state‐of‐the‐art computations utilizing the FC‐HT1|VH model at the CAM−B3LYP/def2‐TZVP level, we unveiled the paramount impact of Franck–Condon (FC), Herzberg‐Teller (HT), and Duschinsky effects on their chiroptical responses. Our research underscores the pivotal role of structural deformations associated with the S1‐to‐S0 electronic transition in molding CPL spectra and wavelength‐dependent dissymmetry (g) factor values, as well as the significance of HT effects in shaping and enhancing CPL responses. This extensive investigation not only advances our comprehension of the vibronic characteristics in configurationally distinct double helicenes but also offers valuable insights for the design of chiral molecules featuring controllable or finely‐tunable CPL responses. [ABSTRACT FROM AUTHOR]

A negatively curved aza‐nanographene (NG) containing two octagons was synthesized by a regioselective and stepwise cyclodehydrogenation procedure, in which a double aza[7]helicene was simultaneously formed as an intermediate. Their saddle‐shaped structures with negative curvature were unambiguously confirmed by X‐ray crystallography, thereby enabling the exploration of the structure–property relationship by photophysical, electrochemical and conformational studies. Moreover, the assembly of the octagon‐embedded aza‐NG with fullerenes was probed by fluorescence spectral titration, with record‐high binding constants (Ka=9.5×103 M−1 with C60, Ka=3.7×104 M−1 with C70) found among reported negatively curved polycyclic aromatic compounds. The tight association of aza‐NG with C60 was further elucidated by X‐ray diffraction analysis of their co‐crystal, which showed the formation of a 1 : 1 complex with substantial concave‐convex interactions. [ABSTRACT FROM AUTHOR]

6,10‐Dipropyl‐5,9‐diaza[5]‐ and ‐[6]helicene were synthesized by ortho,ortho' fusion of ortho‐teraryldicarboxamides. Key steps in the synthesis of the teraryls are azide formation with subsequent reduction and amidation followed by Suzuki cross couplings. The ortho fusions were achieved with phosphorus pentoxide and phosphoryl oxide. The total syntheses could be accomplished with 10 % and 3 %, respectively, in seven consecutive steps starting with meta‐dibromobenzene. The helicenes were investigated by UV/Vis and fluorescence spectroscopy and by quantum chemical calculation of, inter alia, the HOMO‐LUMO gaps. Racemization barriers of the helicenes were calculated, whereupon the optical resolution of 5,9‐diaza[6]helicene was attempted and carried out successfully; ECD spectra were measured of its enantiomers. [ABSTRACT FROM AUTHOR]

We investigate the relative stability of increasingly large helicenes at the CCSD(T) level via the high-level G4(MP2) thermochemical protocol. The relative energies of [n]helicenes (n = 4–9) are obtained via the following reaction: [n]helicene + benzene → [n + 1]helicene + ethene. This reaction conserves the number of sp2-hybridized carbons, the number of aromatic rings, and the helical structures on the two sides of the reaction. We show that the reaction energy converges to an asymptotic value of ΔH298 = + 22.4 kJ/mol for increasingly large helicenes. For comparison, for [n]acenes, the same reaction converges to a much higher asymptotic reaction enthalpy of ΔH298 = + 56.8 kJ/mol. This difference between the two asymptotic reaction enthalpies sheds light on the relative thermodynamic stability of increasingly large helicenes. We proceed to use the G4(MP2) reaction energies to evaluate the performance of dispersion-corrected density functional theory (DFT) and semiempirical molecular orbital (SMO) methods for the relative energies of [n]helicenes. Nearly all DFT methods perform poorly with root-mean-square deviations (RMSDs) above 10 kJ/mol. The best-performing DFT method, BLYP-D4, attains an RMSD = 5.2 kJ/mol. Surprisingly, the advanced SMO methods, XTB and PM7, outperform the DFT methods and result in RMSDs of 3.0 and 3.1 kJ/mol, respectively. [ABSTRACT FROM AUTHOR]

The π-stacking interaction is one of the most important intramolecular and intermolecular noncovalent interactions in organic chemistry. It plays an important role in stabilizing some structures and transition states in certain reactions via both intramolecular and intermolecular interactions, facilitating different selectivities, such as chemo-, regio-, and stereoselectivities. This minireview focuses on the recent examples of the π-stacking interaction-controlled asymmetric synthesis, including auxiliary-induced asymmetric synthesis, kinetic resolution, asymmetric synthesis of helicenes and heterohelicenes, and multilayer 3D chiral molecules. [ABSTRACT FROM AUTHOR]

This review focuses on obtaining embedded azulene polycyclic molecules treated according to their particular structure. The division of material into the azulene unit grafted only on one or two bonds and poly-fused azulene compounds was suggested with the intention of facilitating the presentation and assimilation of information. The similarity of some structural features in the compounds included in different analyzed classes results in the presence of the same synthesis protocol in several places. Obtaining benz[a]azulenes, azulene-fused acenes, and helicenes or azulene-embedded nanographene, along with other compounds, is presented. [ABSTRACT FROM AUTHOR]