Non-Fullerene Electron Acceptors Based on Hybridisation of Corannulene and Thiophene-S,S-Dioxide Motifs

Herein we show that hybridisation of buckybowl corannulene and thiophene-S,S-dioxide motifs is a general approach for the preparation of high electron affinity molecular materials. The devised synthesis is modular and relies on thienannulation of corannnulene-based phenylacetylene scaffolds. The final compounds are highly soluble in common organic solvents. These compounds also exhibit interesting optical properties such as absorption and emission in the blue/green regions of the electromagnetic spectrum. Importantly, a bis-S,S-dioxide derivative exhibits three reversible reductions similar in their strength to the prevalent fullerene-based electron acceptor phenyl-C₆₁ -butyric acid methyl ester (PC₆₁ BM).

A Strategy for Polar Crystals with Dipolar Heterohelicenes

Polar crystals have attracted interest for the applications to polar materials with piezo- and pyroelectricity, and second harmonic generation. Despite their potential utility for flexible polar materials, a strategy for ordering polar helicenes have remained elusive. Here, we demonstrate creation of polar crystal with unsymmetrically substituted aza[5]helicenes tuned by substituents. The usymmetric aza[5]helicenes have been prepared through regioselective monoprotiodesilylations. We disclosed triisopropylsilyl-substituted derivatives show 1D chain columnar packings. In particular, enantiopure crystals showed spontaneous polarization. Optical and single-crystal X-ray diffraction experiments with other derivatives, as well as theoretical calculations, revealed that the presence of triisopropylsilyl or electron-withdrawing aryl substituents is essential for forming the 1D chain columnar structure. Hirshfeld surface analyses further showed that CH-π interactions between 1D chain columns regulate the polar assembly. Finally, we determined the polarizability of the nitro derivative by ab initio calculation to be 4.53 µC/cm 2 . This value corroborates the first example of a spontaneously polar crystal of helicenes. We believe that this study will contribute to the development of polar materials from organic molecules.

Theoretical study of the mixed π-conjugated bridge effect on the nonlinear optical properties of corannulene derivative

A new series of corannulene derivatives with two mixed π-conjugated bridge have been theoretically designed and investigated by means of density functional theory. It is found that all molecules exhibit large energy gaps. The holes and electrons analysis show that charge transfer from long-chain connected with NH₂ to long-chain connected with NO₂. The small transition energy brings corannulene derivatives larger first hyperpolarizabilities. Furthermore, the polarization scan of the hyper-Rayleigh scattering (HRS) intensity indicates that all studied compounds belong to dipolar characteristic. The results indicate that employing two mixed π-conjugated bridge can significantly increase the first hyperpolarizability.

Corannulene Chalcogenides

The introduction of chalcogen atoms into a polycyclic aromatic hydrocarbon structure is an established method to tune material properties. In the context of corannulene (C₂₀ H₁₀ ), a fragment of fullerene C₆₀ , such structural adjustments have given rise to an emerging class of functional and responsive molecular materials. In this minireview, our aim is to discuss the synthesis and properties of such chalcogen (sulfur, selenium, and tellurium) derivatives of corannulene.

Corannulene-Based Electron Acceptors: Combining Modular and Practical Synthesis with Electron Affinity and Solubility

It is shown in this work that high electron affinity can be combined with high solubility and practical accessibility in corannulene-based electron acceptors. The electron affinity originates from the presence of three different types of electron-withdrawing groups (imide, sulfone, and trifluoromethyl) on the aromatic scaffold. The imide substituent further hosts a long alkyl chain (C₁₈ H₃₇ ) to boast solubility in a wide range of organic solvents. The synthesis is modular and consists of three simple steps from a commonly available corannulene derivative with an overall isolated yield of 22-27 %.

Homolytic Versus Heterolytic Bond Breaking in Functionalized [R-C20 H10 ]+ Systems

The comprehensive theoretical investigation of stability of functionalized corannulene cations [R-C₂₀ H₁₀ ]⁺ with respect to two alternative bond-breaking mechanisms, namely, homolytic or radical ([R-C₂₀ H₁₀ ]⁺  → R^•  + C₂₀ H₁₀ ^+• ) and heterolytic or cationic ([R-C₂₀ H₁₀ ]⁺  → R⁺  + C₂₀ H₁₀ ), was accomplished. The special focus was on the influence of the nature of R-group on the energetics of the bond cleavage. Detailed study of energetics of both mechanisms has revealed that the systems with small alkyl groups such as methyl tend to undergo bond breaking in accordance with homolytic mechanism. Subsequent elongation of the chain of the R-group resulted in shifting the paradigm, making heterolytic path more energetically favorable. Subsequent analysis of different components of the bonding between R-group and corannulene polyaromatic core helped to shed light on trends observed. In both mechanisms, the covalent contribution was found to be dominating, whereas ionic part contributes ~25-27%. Two leading components of ΔE_orb , C₂₀ H₁₀ → R and R → C₂₀ H₁₀ , were identified with NOCV-EDA approach. While the homolytic pathway is best described as R → C₂₀ H₁₀ process, the heterolytic mechanism shows domination of the C₂₀ H₁₀ → R term. Surprisingly, the preparation energy (ΔE_prep ) was identified as a key player in stability tendencies found. In other words, the relative stability of corresponding molecular fragments (here R-groups as the corannulene fragment remains the same for all systems) in their cationic or radical forms determine the preference given to a specific bond breaking path and, as consequence, the total stability of target functionalized cations. These conclusions were further confirmed by extending a set of R-groups to conjugated (allyl, phenyl), bulky (iPr, tBu), β-silyl (CH₂ SiH₃ , CH₂ SiMe₃ ), and benzyl (CH₂ Ph) groups. © 2019 Wiley Periodicals, Inc.

Azaindenocorannulenes: Synthesis, Properties, and Chirality

Palladium-catalyzed intramolecular arylation provides bowl-shaped azaindenocorannulenes 7-9. Crystals of 8 show bowl-in-bowl columnar stacking. A substituent model rationalizes the first reduction potential of 18 related molecular bowls. The absolute configurations of bowls 7 and 9 are correlated with VCD and ECD spectra. The bowl inversion barrier of 9 (>190 kJ/mol) shows it to be more inert configurationally than chiral biaryl, phosphenes, or [ n]helicenes.

Corannulenes with Electron-Withdrawing Substituents: Synthetic Approaches and Resulting Structural and Electronic Properties

Corannulene is a multifaceted polyaromatic compound. It has many interesting properties; for example, it has a bowl-shaped molecular structure that, in addition, undergoes a dynamic inversion process. It has attracted much attention within the last decades. This is not only due to its structural properties but also its electronic properties and its various potential applications to materials chemistry. Here, synthetic approaches towards corannulene derivatives with electron-withdrawing substituents are summarized. This includes both selective and unselective methods. Further, the electrochemical properties, that is, the reduction potentials, are analyzed and compared. As a main conclusion, one can state that the electron affinity depends roughly linearly on the number of substituents. Finally, the structural behavior of the substituted buckybowls in the solid state is highlighted. This also allows a general statement about the influence of the electronic and steric nature of substituents on the molecular structures and the solid-state packing of the corannulene derivatives.

Polymeric Nanomaterials Based on the Buckybowl Motif: Synthesis through Ring-Opening Metathesis Polymerization and Energy Storage Applications

Ring-opening metathesis polymerization (ROMP) of buckybowl corannulene-based oxa-norbornadiene monomer is shown to give rise to polymeric nanomaterials with an average pore size of about 1.4 nm and a surface area of 49.2 m²/g. Application in supercapacitor devices show that the corannulene-based nanomaterials exhibit a specific capacitance of 134 F·g^-1 (1.0 V voltage window) in a three-electrode cell configuration. Moreover, the electrode assembled from these materials in a symmetric configuration (1.6 V voltage window) exhibits long-term cyclability of 90% capacitance retention after undergoing 10000 cycles. This work demonstrates that ROMP is a valuable method in synthesizing nanostructured corannulene polymers, and that materials based on the nonplanar polycyclic aromatic motif represents an attractive active component for fabrication of devices targeted at electrochemical energy storage applications.

Amphiphilic Corannulene Derivatives: Synthetic Access and Development of a Structure/Property Relationship in Thermoresponsive Buckybowl Amphiphiles

Eight new derivatives of corannulene have been synthesized, characterized, and examined for their water solubility and thermally triggered assembly behavior. To achieve this, the hydrophobic corannulene core was attached to the hydrophilic polyethylene glycol arm(s). Here, the substitution pattern as well as the arm length was varied systematically. Furthermore, the hydrophobic/hydrophilic ratio was adjusted by incorporating a phenyl ring at the junction point of the two moieties. A properties study revealed that a proper balance among the number, length, and chemical nature of the arm was required to ensure water solubility and thermoresponsive character. Remarkably, the lower critical solution temperature could be modulated within the range of 30-50 °C simply through adjusting the molecular structure of the assembling building block. This work, therefore, demonstrates synthetic feasibility of a wide range of amphiphilic corannulene derivatives and opportunity for modulation of their thermoresponsive behavior.

π-Extended fluoranthene imide derivatives: synthesis, structures, and electronic and optical properties

Diels–Alder reactions of acenaphthylene-5,6-dicarboximide (AI) derivatives with the corresponding dienes afforded some derivatives of π-extended fluoranthene imide, namely N-(2-ethylhexyl)-7,10-diphenylfluoranthene imide (DPFI) and N-(2-ethylhexyl)-7,8,9,10-tetraphenylfluoranthene imide (TPFI), N-(n-octyl)-benzo[k]fluoranthene imide (BFI), and N-(n-octyl)-naphtho[k]fluoranthene imide (NFI). Molecular structures of TPFI and BFI reveal that the core π-skeletons have a highly planar structure, and the molecules form a dimeric structure in the crystals. The absorption spectra exhibit bathochromic shift with π-extension of the core π-skeletons. On the other hand, DPFI and TPFI show the long-wavelength emission related to BFI, probably due to π-extension toward the phenyl substituents in the excited states. BFI and NFI exhibited an interesting concentration-dependent 1H-NMR behavior in CDCl3, suggesting self-aggregation formation. Moreover, BFI and NFI show moderate and remarkable solvatofluorochromism in solutions (BFI for ΔλEM = 67 nm, NFI for ΔλEM = 116 nm), respectively, while DPFI and TPFI show weak solvatofluorochromism. The density functional theory calculations demonstrate that the considerable spatial separation between the HOMO and LUMO coefficients in the NFI molecule. The result indicates that the ground-to-excited state transition of NFI should have intramolecular charge transfer (ICT) character.

Concave binding of cationic Li to quadrannulene

Concave binding of cationic Li to quadrannulene and its influence on buckybowl functionalization are introduced using DFT calculations.

Stability of functionalized corannulene cations [R-C20 H10 ](+) : An influence of the nature of R-Group

The first comprehensive theoretical study of stability of hub-functionalized corannulene cations [R-C20 H10 ](+) as the function of the nature of R-group was accomplished. The initial set of linear alkyl R-group of different length (R=(CH2 )n CH3 , n = 0-9) was augmented by groups which form stable organic cations, such as tert-butyl, isopropyl, allyl, and phenyl. Investigation of relative stability (with bonding energy as the measure) was accompanied by detailed study of changes in aromaticity using a large set of descriptors, as well as by the evaluation of energetics of possible migration of R-group from the hub-site to the spoke-position. Decrease in stability of functionalized corannulene cations with lengthening of R-group and/or replacing it with branched alkyl group was found to be the general trend. At the same time, π-conjugated groups such as allyl or phenyl ones, stabilize the system. All methods/approaches applied unambiguously indicated that the actual stability of the hub-functionalized corannulene cations is indeed a multi faceted phenomenon. Important contributions come from different interplay between attractive (ΔEorb vs. ΔEelstat ) and repulsive (ΔEPauli ) components of the bonding, from changes in aromatic behavior of rings in polyaromatic fragment, and from activation barrier for the process of migration of R-group. © 2016 Wiley Periodicals, Inc.

Buckybowls: Corannulene and Its Derivatives

Corannulene, a kind of bowl like polycyclic aromatic hydrocarbon (PAH), whose molecule is composed of a central pentagon and five closely adjacent hexagons on the pentagon's five sides, has received great scientific interest among research groups. In this review, the syntheses, characteristic molecule structure and properties of corannulene are clarified, as well as its derivatives with different substituted groups, fused derivatives, metal complex, and derivatives for host guest chemistry. On the basis of reviewing the applications and properties of corannulene together with its derivatives, the potential applications in hydrogen storage and lithium storage were highlighted and prospected.

Aromatic stabilization of functionalized corannulene cations

The first comprehensive theoretical investigation of aromaticity in functionalized corannulene cations of general formula [CH3-C20H10](+) was accomplished. The experimentally known system [CH3-hub-C20H10](+) was augmented by two other possible isomers, namely, rim- and spoke-ones. Changes in aromaticity, when going from neutral corannulene to its functionalized cations, were monitored with the help of descriptors of different nature such as structure-based HOMA, topological PDI and FLU, and magnetic NICS. A highly efficient tool for analysis and visualization of delocalization and conjugation named ACID was also utilized. In the final step, a complete set of (1)H and (13)C chemical shifts was calculated and compared with the available experimental data. Conservation of aromaticity of 6-membered rings along with vanishing anti-aromatic character of central 5-membered rings was found to be the main reason for the exceptional stability of the hub-isomer. At the same time, functionalization of the corannulene moiety at the rim- or spoke-site resulted in dramatic elimination of aromaticity of 6-membered rings, whereas anti-aromatic character of the central ring remained. Altogether, it led to much lower stability of these isomers in comparison with that of the hub-one.

Host–guest interaction between corannulene and γ-cyclodextrin: mass spectrometric evidence of a 1 : 1 inclusion complex formation

The toroidal cavity of γ-cyclodextrin is shown to interact with a bowl-shaped polycyclic aromatic hydrocarbon, corannulene, through host–guest interactions.

Functionalized corannulene carbocations: a structural overview

A detailed structural overview of a family of bowl-shaped polycyclic aromatic carbocations of the type [C20 H10 R](+) with different R functionalities tethered to the interior surface of corannulene (C20 H10 ) is provided. Changing the identity of the surface-bound groups through alkyl chains spanning from one to four carbon atoms and incorporating a different degree of halogenation has led to the fine tuning of the bowl structures and properties. The deformation of the corannulene core upon functionalization has been revealed based on X-ray crystallographic analysis and compared for the series of cations with R=CH3 , CH2 Cl, CHCl2 , CCl3 , CH2 CH3 , CH2 CH2 Cl, and CH2 CH2 Br. The resulting carbocations have been isolated with several metal-based counterions, varying in size and coordinating abilities ([AlCl4 ](-) , [AlBr4 ](-) , [(SnCl)(GaCl4 )2 ](-) , and [Al(OC(CF3 )3 )4 ](-) ). A variety of aggregation patterns in the solid state has been revealed based on different intermolecular interactions ranging from cation-anion to π-π stacking and to halogen⋅⋅⋅π interactions. For the [C20 H10 CH2 Cl](+) ion crystallized with several different counterions, the conformation of the R group attached to the central five-membered ring of corannulene moiety was found to depend on the solid-state environment defined by the identity of anions. Solution NMR and UV/Vis investigations have been used to complement the X-ray diffraction studies for this series of corannulene-based cations and to demonstrate their different association patterns with the solvent molecules.

Thiophene-fused bowl-shaped polycyclic aromatics with a dibenzo[a,g]corannulene core for organic field-effect transistors

Electron-rich thiophene units were fused into the skeleton of corannulene to extend π-surfaces and tune arrangement in a single crystal.

Corannulene derivatives with low LUMO levels and dense convex–concave packing for n-channel organic field-effect transistors

N-channel OFETs in air based on corannulenes through lowering their LUMO levels and packing the molecules densely in single crystals were achieved.

Fluorinated and trifluoromethylated corannulenes

The syntheses and properties of corannulenes carrying electron-withdrawing groups (F, CF3 , C6 F5 ) are reported. Direct fluorination of corannulene (C20 H10 ) was carried out with xenon difluoride, and the crystal structure of the product was confirmed by the X-ray analysis. Novel trifluoromethylated corannulenes, including the versatile 4,9-dibromo-1,2-bis(trifluoromethyl)corannulene, were obtained by various established ring-closing reactions. Besides the use of hexafluorobutyne for the construction of fluoranthenes by Diels-Alder reaction as precursor molecules to form 1,2-disubstituted corannulenes, bis(pentafluorophenyl)acetylene was employed as dienophile. The molecular structure and crystal packing of a trifluoromethylated corannulene was determined by single-crystal X-ray analysis and compared with those known brominated and trifluoromethylated corannulenes. The general electron-acceptor properties of corannulenes bearing substituents introduced in particular positions by liquid-phase synthesis are discussed together with published computational results.