Supramolecular trapping of a cationic all-metal σ-aromatic {Bi4} ring

Aromaticity in organic molecules is well defined, but its role in metal-only rings remains controversial. Here we introduce a supramolecular stabilization approach of a cationic {Bi4} rhomboid within the symmetric charge sphere of two bowl-shaped dianionic calix[4]pyrrolato indinates. Crystallographic and spectroscopic characterization, quantum chemical analysis and magnetically induced ring currents indicate σ-aromaticity in the formally tetracationic 16-valence electron [Bi4]4+ ring. Computational screening for other p-block elements identifies the planar rhomboid as the globally preferred structure for 16-valence electron four-atomic clusters. The aromatic [Bi4]4+ is isoelectronic to the [Al4]4-, a motif previously observed as antiaromatic in Li3[Al4]- in the gas phase. Thus, subtle factors such as charge isotropy seem to decide over aromaticity or antiaromaticity, advising for caution in debates based on the Hückel model-a concept valid for second-row elements but less deterministic for the heavier congeners.

A corannulene-based metallobox for the encapsulation of fullerenes

A corannulene-bis-N-imidazolium salt was used for the synthesis of two corannulene-bis-N-heterocyclic carbenes of dirhodium(i) complexes of formula (corannulene-di-NHC)[RhCl(COD)]2 and (corannulene-di-NHC)[RhCl(CO)2]2. Both complexes were characterized by spectroscopic techniques, and the electron-donating properties of the corannulene-di-NHC ligand were studied by means of infrared spectroscopy and cyclic voltammetry. The complex (corannulene-di-NHC)[RhCl(COD)]2 was used for the encapsulation of fullerenes C60 and C70, generating host-guest complexes with 2 : 1 stoichiometry, as evidenced by 1H NMR and ITC titrations. Then, a tetra-rhodium(i) metallo-rectangle supported by two corannulene-bis-imidazolylidene ligands and two cofacial 4,4'-bipyridine ligands was prepared and characterized. This metallobox is capable of quantitatively encapsulating fullerenes C60 and C70, forming complexes that are highly stable even at high temperatures. The molecular structure of the metallobox with encapsulated C60 reveals a perfect size and shape complementarity that benefits from the concave-convex π-π interaction between the polyaromatic surfaces of the host and the guest.

Metal cations recognition by bowl-shaped N-pyrrolic polycyclic aromatic hydrocarbons

Bowl-shaped, nitrogen-doped polycyclic aromatic hydrocarbons were examined for the first time as molecular receptors for the recognition of metal cations. Potentiometric and spectrofluorimetric assays, supported with density functional theory computations, revealed that the title compounds recognise metal cations with a special focus on caesium (Cs+) cations.

Impact of doping with organic dopants and mixed doping with alkali metals and organic dopants on the absorption, electronic, optoelectronic, thermodynamic and nonlinear optical properties of dibenzo[b,def]chrysene in gaseous media: DFT and TD-DFT studies

CONTEXT

In this study, we evaluate the geometrical, absorption, optoelectronic, electronic, nonlinear optical (NLO) and thermodynamic properties of dibenzo[b,def]chrysene molecule derivatives by means of DFT and TD-DFT simulations. In view of the aim of producing new high-performance materials for non-linear optics (NLO) by doping test, two types of doping were used. We obtained six derivatives by doping with organic dopants (Nitro, amide and ticyanoethenyl) and mixed alkali metal (potassium) and organic dopants. Doping with organic dopants produced molecules A, B and C, respectively when substituting one hydrogen with nitro (NO2), amide (CONH2) and tricyanoethenyl (C5N3) groups, while mixed doping involved considering A, B and C and then substituting two hydrogens with two potassiums to obtain compounds D, E and F respectively. The negative values of the various interaction energies calculated for all the doped molecules show that they are all stable, but also that molecules C and F are the most stable in the case of both dopings. The gap energies calculated at the B3LYP level of theory are all below 3 eV, which means that all the molecules obtained are semiconductors. Better still, compounds C and F, with gap energies of 1.852 eV and 1.204 eV, respectively, corresponding to decreases of 35.67% and 58.18% in gap energy compared with the pristine molecule, are more reactive than the other doped molecules. Mixed doping is therefore a highly effective way of narrowing the energy gap and boosting the semiconducting character and reactivity of organic materials. Optoelectronic properties have also been improved, with refractive index values higher than those of the reference material, glass. This shows that our compounds could be used under very high electric field conditions of the order of 4.164 × 109 V.m-1 for C and 7.410 × 109 V.m-1 for F the highest values at the B3LYP level of theory. The maximum first-order hyperpolarizability values for both types of doping are obtained at the CAM-B3LYP level of theory by C:β mol = 92.088 × 10-30esu and by F:β mol = 129.449 × 10-30esu, and second-order values are also given by these same compounds. These values are higher than the reference value, which is urea, making our compounds potential candidates for high-performance NLO applications. In dynamic mode and at a frequency of 1064 nm, at the CAM-B3LYP level of theory, the highest dynamic hyperpolarizability coefficients were obtained by C and F. Hyper-Rayleigh scattering β HRS , coefficients of the electro-optical Pockel effect (EOPE), EFISHG, third-order NLO-response degree four-wave mixingγ DFWM , quadratic nonlinear refractive index n2 were also calculated. The maximum values of n2 are obtained by C (6.13 × 10-20 m2/W) and F (6.60 × 10-20 m2/W), these values are 2.24 times higher than that of fused silica which is the reference for degenerate four-wave mixing so our molecules could also have applications in optoelectronics as wavelength converters, optical pulse modulators and optical switches.

METHODS

Using the DFT method, we were able to determine the optimized and stable electronic structures of doped dibenzo[b,def]chrysene derivatives in the gas phase. We limited ourselves to using the proven B3LYP and CAMB3LYP levels of theory for calculating electronic properties, and non-linear optics with the 6-311G +  + (d,p) basis set, which is a large basis set frequently used for these types of compound. Gaussian 09 software was used to run our calculations, and Gauss View 6.0.16 was used to visualize the output files. TD-DFT was also used to determine absorption properties at the B3LYP level of theory, using the same basis set.

Bowl-Shaped Kekulene Analogues: Cycloarenes with two Five-Membered Rings

Kekulene, a cycloarene composed of 12 fused benzene rings in a circular arrangement, exhibits a highly planar and robust structure. Kekulene has been the subject of investigation into its aromaticity and electronic structure, particularly in relation to the cyclic benzenoid. We have successfully synthesized novel bowl-shaped kekulene analogues with five-membered rings incorporated into the kekulene structure. The results of DFT calculations and VT-NMR spectra indicate that inversion of their concave-convex structures occurs at room temperature. The NICS and AICD plots predict that the Clar's type resonance structure is found in a manner analogous to the pristine kekulene, albeit with the interruption of the π-conjugation on the sp3 carbons at the five-membered rings. Despite the presence of the Clar's resonance structure, the Diels-Alder reaction proceeded smoothly with a dienophile, in contrast to the behavior of planar kekulene derivatives. This study will lead to the creation of novel bowl-shaped compounds and development of reactivity in aromatic compounds.

Formation of Nitrogen-Doped Positively Curved Molecules by π-Extension

Two nitrogen-doped positively curved aromatic molecules bearing doubly fused pentagonal rings were synthesized and characterized. Crystallographic analysis confirms the formation of a bowl-shaped structure, which is induced by the fusion of adjacent pentagons to the rigid aromatic planes. Both compounds demonstrate good photoluminescence. These electron-rich bowl-shaped molecules can associate with C60 to form complexes in 2:1 ratio in toluene with different association constants depending on the molecular dimension of the hosts.

Extended Quinolizinium-Fused Corannulene Derivatives: Synthesis and Properties

Reported here is the design and synthesis of a novel class of extended quinolizinium-fused corannulene derivatives with curved geometry. These intriguing molecules were synthesized through a rationally designed synthetic strategy, utilizing double Skraup-Doebner-Von Miller quinoline synthesis and a rhodium-catalyzed C-H activation/annulation (CHAA) as the key steps. Single-crystal X-ray analysis revealed a bowl depth of 1.28-1.50 Å and a unique "windmill-like" shape packing of 12a(2PF6-) due to the curvature and incorporation of two aminium ions. All of the newly reported curved salts exhibit green to orange fluorescence with enhanced quantum yields (Φf = 9-13%) and improved dispersibility compared to the pristine corannulene (Φf = 1%). The reduced optical energy gap and lower energy frontier orbital found by doping extended corannulene systems with nitrogen cations was investigated by UV-vis, fluorescence, and theoretical calculations. Electrochemical measurements reveal a greater electron-accepting behavior compared with that of their pyridine analogues. The successful synthesis, isolation, and evaluation of these curved salts provide a fresh perspective and opportunity for the design of cationic nitrogen-doped curved aromatic hydrocarbon-based materials.

Beyond Planar Structure: Curved π-Conjugated Molecules for High-Performing and Stable Perovskite Solar Cells

Perovskite solar cell (PSC) shows a great potential to become the next-generation photovoltaic technology, which has stimulated researchers to engineer materials and to innovate device architectures for promoting device performance and stability. As the power conversion efficiency (PCE) keeps advancing, the importance of exploring multifunctional materials for the PSCs has been increasingly recognized. Considerable attention has been directed to the design and synthesis of novel organic π-conjugated molecules, particularly the emerging curved ones, which can perform various unmatched functions for PSCs. In this review, the characteristics of three representative such curved π-conjugated molecules (fullerene, corannulene and helicene) and the recent progress concerning the application of these molecules in state-of-the-art PSCs are summarized and discussed holistically. With this discussion, we hope to provide a fresh perspective on the structure-property relation of these unique materials toward high-performance and high-stability PSCs.

Unraveling the role of superalkalis in modulating the static and dynamic hyperpolarizabilities of emerging calix[4]arenes

Calixarenes, as novel organic materials, can play a pivotal role in the development of high-performance nonlinear optical materials due to the ease of design and fabrication. In this study, DFT simulations were employed to investigate the geometric, electronic, and NLO responses of calix[4]arene doped with Li3O, Na3O, and K3O superalkalis. The computed values of the vertical ionization energies and interaction energies indicate the chemical and thermodynamic stabilities of the targeted M3O@calix[4]arene complexes. The corresponding energy gaps (2.01 to 3.49 eV) are notably reduced, indicating the semiconductor nature of the materials. Surprisingly, the M3O@calix[4]arene complexes exhibit transparency in the UV/visible range as the absorption peaks are shifted in the near infrared (NIR) region. The highest values of 5.9 × 105 a.u. and 2.3 × 108 a.u. for the respective first and second hyperpolarizabilities are observed for Na3O@calix[4]arene. Furthermore, the Na3O@calix[4]arene complex exhibits maximum values of 2.3 × 105 a.u. for second harmonic generation (SHG) and (K3O@calix[4]arene) 2.3 × 106 a.u. for the electro-optical Pockels effect (EOPE) at 1064 nm. Similarly, approximations are made for the dynamic second hyperpolarizability coefficients (EOKE and EFISHG) at different wavelengths. Notably, the Na3O@calix[4]arene complex demonstrates the highest quadratic nonlinear refractive index (n2) of 9.5 × 10-15 cm2 W-1 at 1064 nm. This research paves the way for the development of stable calix[4]arenes doped with superalkalis, leading to an improved nonlinear optical (NLO) response.

Mechanochemical Synthesis of Corannulene: Scalable and Efficient Preparation of A Curved Polycyclic Aromatic Hydrocarbon under Ball Milling Conditions

Corannulene, a curved polycyclic aromatic hydrocarbon, is prepared in a multigram scale through mechanochemical synthesis. Initially, a mixer mill approach is examined and found to be suitable for a gram scale synthesis. For larger scales, planetary mills are used. For instance, 15 g of corannulene could be obtained in a single milling cycle with an isolated yield of 90 %. The yields are lower when the jar rotation rate is lower or higher than 400 revolutions per minute (rpm). Cumulatively, 98 g of corannulene is produced through the ball milling-based grinding techniques. These results indicate the future potential of mechanochemistry in the rational chemical synthesis of highly curved nanocarbons such as fullerenes and carbon nanotubes.

Molecular modeling of the structural, electronic, excited state dynamic, and the photovoltaic properties of the oligomers of n-corannulene (n = 1-4)

Despite the fact that n-corannulene oligomers (n = 1-4) have a variety of electronic and optical properties, including the ability to be tuned and the potential to be used as light-harvesting materials, there has not been a computational assessment of their structural, electronic, and optical properties. Herein, a computational evaluation of the concerned materials regarding their potent use in solar cell technology has been conducted via DFT/CAM-B3LYP and M062X/6-311+G level of theory. It was observed that the calculated 1st frequency of the n-Corannulene (n = 1-4) were 144.15, 106.36, 48.96 and 42.21 respectively. Notably, the computed cohesive energy value increased as the number of Corannulene units increases while the electronic characteristics revealed that the chemical activity of the structures increased as the number of oligomers rose. Both calculation techniques demonstrate that the number of n-Corannulene oligomers increases the HOMO energy while decreasing the LUMO energy based on the external electric field (EF) effect. The findings demonstrated that as EF intensity increases, the energy gap (Eg/eV = |EHOMO-ELUMO|) of these molecular systems decreases which can be attributed to a decrease in the electron transfer potential barrier. The 4-Corannulene systems showed the highest wave length of adsorption for the investigated compound at 546.18 nm, with the highest oscillator strength of 0.2708 and the lowest transition energy of 2.2700 eV, arising from S0-S1 (H-L) and the highest major percentage contribution of 93.34 % in comparison to the investigated compounds. We are hopeful that this research will help experimental researchers understand the potential of n-Corannulene, specifically 4-corannulene, as powerful material for a variety of applications ranging from solar cell, photovoltaic properties and many others.

Multiply exo-Methylated Corannulenes

The curved π-conjugated surface of bowl-shaped corannulene has been multiply methylated to form exo-di-, -tetra-, and -hexamethylated corannulenes. The multimethylations became possible through in-situ iterative reduction/methylation sequences that involve the reduction of corannulenes using sodium to form the anionic corannulene species, and the subsequent SN 2 reaction of the anionic species with reduction-resistant dimethyl sulfate. X-ray diffraction analyses, NMR, MS, UV-Vis measurements, and DFT calculations have revealed the molecular structures of the multimethylated corannulenes and the sequence of the multimethylation. This work has the potential to contribute to the controlled synthesis and characterizations of multifunctionalized fullerenes.

Thiol-epoxy 'click' chemistry: a focus on molecular attributes in the context of polymer chemistry

Base-catalyzed ring-opening reaction of epoxides with the thiol nucleophiles is useful in the preparation and post-polymerization modification of synthetic polymers. Due to its many beneficial characteristics, this process is referred to as the thiol-epoxy 'click' reaction. In this article, our aim is to discuss the fundamental attributes of this process by tracing our own steps in the field. We initially address the aspects of efficiency, regio-selectivity, stoichiometry, and reaction conditions with the help of linear, hyperbranched, graft, dendritic, and cross-linked poly(β-hydroxy thioether)s. A special emphasis is placed on hydrogel synthesis and photopolymerization on surfaces. Subsequently, quenching of the alkoxide anion is considered which is a critical step in the formation of the β-hydroxy thioether linkage upon completion of reaction. The amenability of further reaction on the hydroxy and thioether groups through esterification and sulfur alkylation is then discussed. Initially, post-gelation/fabrication modification of sulfide linkages is considered to obtain cationic sulfonium hydrogels and zwitterionic photopatterned networks with antibacterial and antibiofouling properties, respectively. A post-synthesis functionalization strategy is then described to access same centered and segregated main-chain poly(β-hydroxy sulfonium)s as potent antibacterial materials. In side-chain polysulfides, the sequential post-synthesis modifications involving poly(glycidyl methacrylate) scaffolds can lead to the formation of amphiphilic homopolymers. The application of such materials is discussed in the arena of siRNA delivery. Finally, concerns relating to the formation of disulfide defects and open research goals such as study of the orthogonality of the reaction are addressed.

Recent Advances in Applications of Fluorescent Perylenediimide and Perylenemonoimide Dyes in Bioimaging, Photothermal and Photodynamic Therapy

The emblematic perylenediimide (PDI) motif which was initially used as a simple dye has undergone incredible development in recent decades. The increasing power of synthetic organic chemistry has allowed it to decorate PDIs to achieve highly functional dyes. As these PDI derivatives combine thermal, chemical and photostability, with an additional high absorption coefficient and near-unity fluorescence quantum yield, they have been widely studied for applications in materials science, particularly in photovoltaics. Although PDIs have always been in the spotlight, their asymmetric counterparts, perylenemonoimide (PMI) analogues, are now experiencing a resurgence of interest with new efforts to create architectures with equally exciting properties. Namely, their exceptional fluorescence properties have recently been used to develop novel systems for applications in bioimaging, biosensing and photodynamic therapy. This review covers the state of the art in the synthesis, photophysical characterizations and recently reported applications demonstrating the versatility of these two sister PDI and PMI compounds. The objective is to show that after well-known applications in materials science, the emerging trends in the use of PDI- and PMI-based derivatives concern very specific biomedicinal applications including drug delivery, diagnostics and theranostics.

Saddle-shaped aza-nanographene with multiple odd-membered rings

A saddle-shaped aza-nanographene containing a central 1,4-dihydropyrrolo[3,2-b]pyrrole (DHPP) has been prepared via a rationally designed four-step synthetic pathway encompassing intramolecular direct arylation, the Scholl reaction, and finally photo-induced radical cyclization. The target non-alternant, nitrogen-embedded polycyclic aromatic hydrocarbon (PAH) incorporates two abutting pentagons between four adjacent heptagons forming unique 7-7-5-5-7-7 topology. Such a combination of odd-membered-ring defects entails a negative Gaussian curvature within its surface with a significant distortion from planarity (saddle height ≈ 4.3 Å). Its absorption and fluorescence maxima are located in the orange-red region, with weak emission originating from the intramolecular charge-transfer character of a low-energy absorption band. Cyclic voltammetry measurements revealed that this stable under ambient conditions aza-nanographene underwent three fully reversible oxidation steps (two one-electron followed by one two-electron) with an exceptionally low first oxidation potential of E _ox1 = -0.38 V (vs. Fc/Fc⁺).

Synthesis and Late-Stage Diversification of BN-Embedded Dibenzocorannulenes as Efficient Fluorescence Organic Light-Emitting Diode Emitters

We report the synthesis and late-stage diversification of a new class of hetero-buckybowl, BN-embedded dibenzocorannulenes (B₂ N₂ -DBCs). The synthesis is achieved via one-shot halogenative borylation, comprising the nitrogen-directed haloboration of alkyne and an intramolecular bora-Friedel-Crafts reaction, which provides BN-embedded dibenzocorannulene possessing two bromo substituents (B₂ N₂ -DBC-Br). B₂ N₂ -DBC-Br undergoes diversification via coupling reactions to provide a variety of arylated derivatives (B₂ N₂ -DBC-R), exhibiting strong blue fluorescence. An organic light-emitting diode (OLED) employing one of the derivatives as an emitter exhibited a high external quantum efficiency of 6.6 % and long operational lifetime of 907 h at an initial luminance of 1000 cd m^-2 , indicating the significant potential for the development of efficient and stable hetero-buckybowl-based OLED materials.

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).

Infrared and Laser-Induced Fluorescence Spectra of Sumanene Isolated in Solid para-Hydrogen

The para-hydrogen (p-H₂) matrix-isolation technique has been scarcely used to record electronic absorption and emission spectra. It is expected that its small matrix shifts due to diminished molecular interactions and the softness of the lattice might be advantageous to help identify the carriers of the diffuse interstellar bands. In this article, we present infrared, fluorescence excitation, and dispersed fluorescence spectra of sumanene (C₂₁H₁₂), a bowl-shaped polycyclic aromatic hydrocarbon and a fragment of C₆₀, isolated in solid p-H₂. The recorded vibrational wavenumbers from infrared and dispersed fluorescence agree with the scaled harmonic vibrational wavenumbers calculated with the B3PW91/6-311++G(2d,2p) and B3LYP/6-311++G(2d,2p) methods. The recorded fluorescence excitation spectra are consistent with the spectra of jet-cooled gas-phase C₂₁H₁₂ reported previously by Kunishige et al. We found a rather small matrix shift of 55 cm^-1 for the S₁-S₀ electronic transition origin located at 27 888 cm^-1. Vibrational wavenumbers associated with the S₁ state of C₂₁H₁₂ inferred from the experimental spectrum can be assigned mostly to fundamental normal modes; they are in satisfactory agreement with scaled harmonic vibrational wavenumbers calculated at the TD-B3PW91/6-311++G(2d,2p) level of theory. Significantly more vibrational modes of the S₁ state were identified as compared with those in the reported gas-phase work. The potential of p-H₂ matrix-isolation spectroscopy to provide electronic excitation spectra suitable for comparison to astronomical observations is discussed by comparing the spectra of C₂₁H₁₂ isolated in solid p-H₂ and in solid Ne, a matrix host commonly employed in astrochemistry.

The Mechanochemical Synthesis and Activation of Carbon-Rich π-Conjugated Materials

Mechanochemistry uses mechanical force to break, form, and manipulate chemical bonds to achieve functional transformations and syntheses. Over the last years, many innovative applications of mechanochemistry have been developed. Specifically for the synthesis and activation of carbon-rich π-conjugated materials, mechanochemistry offers reaction pathways that either are inaccessible with other stimuli, such as light and heat, or improve reaction yields, energy consumption, and substrate scope. Therefore, this review summarizes the recent advances in this research field combining the viewpoints of polymer and trituration mechanochemistry. The highlighted mechanochemical transformations include π-conjugated materials as optical force probes, the force-induced release of small dye molecules, and the mechanochemical synthesis of polyacetylene, carbon allotropes, and other π-conjugated materials.

An Unrevealed Molecular Function of Corannulene Buckybowl Glycoconjugates in Selective Tumor Annihilation by Targeting the Cancer-Specific Warburg Effect

The biomedical application of corannulene π-bowls is historically limited by low solubility and bioavailability despite the potential in their unique electronic properties for new functional materials. Herein, the unexpected role and molecular mechanism of Corranulene π-bowls are uncovered in biomedical applications as an effective anticancer agent for Warburg effect mediated selective tumor targeting. The corannulene triazolyl monosaccharides Cor-sugars exhibit highly potent cytotoxicity against human cancer cells and effectively inhibit xenograft growth of hyperglycolytic tumors. Particularly, the galactose-conjugated Cor-gal exhibits superior in vivo anticancer efficacy in A549 tumor models with outstanding safety profile compared to doxorubicin. Moreover, the combined treatment of Cor-gal with immune checkpoint inhibitor results in an effective synergy in treating H460 human lung carcinoma. An uptake mechanism study reveals that Cor-sugars exploit tumor-specific glucose transporter glucose transporter 1 (GLUT1) for targeted cell delivery and intra-tumoral accumulation through the cancer-specific Warburg effect. Their significant anticancer activity is attributed to multiphasic DNA-binding and cell cycle alteration effects. This study uncovers new molecular properties of corannulene buckybowl and enabling their potential new applications in biomedical engineering.

Corannulene-based acenes

Synthesis of diacenes still represents a considerable challenge due to their poor stability and low solubility.

Synthesis, electronic properties, and self-assembly of an alkylated dibenzo(biscorannulene)

The synthesis and properties of a novel fully-conjugated biscorannulene derivative were reported. This biscorannulene derivative shows self-association in solution and adopts a stacked geometry in crystal.

Diazapentabenzocorannulenium: A Hydrophilic/Biophilic Cationic Buckybowl

Polycyclic aromatic molecules are promising functional materials for a wide range of applications, especially in organic electronics. However, their largely hydrophobic nature has impeded further applications. As such, imparting high solubility/hydrophilicity to polycyclic aromatic molecules leads to a breakthrough in this research field. Herein, we report the synthesis of diazapentabenzocorannulenium, a cationic nitrogen-embedded buckybowl bearing a central imidazolium core, by a bottom-up strategy from polycyclic aromatic azomethine ylide. X-ray crystallography analyses have revealed a bowl-shaped molecular structure that is capable of forming charge-segregated one-dimensional columns by bowl-in-bowl packing. In addition to its fluorescence capabilities and high dispersibility in water, the molecule was found to selectively localize in the mitochondria of various tumor cells, showing potential as viable mitochondria-selective fluorescent probes.

Five-Fold Symmetric Pentaindolo- and Pentakis(benzoindolo)Corannulenes: Unique Structural Dynamics Derived from the Combination of Helical and Bowl Inversions

Peripherally π-extended corannulenes bearing quintuple azahelicene units, 10 and 11, were prepared and their dynamic behaviors were studied experimentally and theoretically. The fused corannulenes were synthesized from sym-pentabromocorannulene in three steps. X-Ray diffraction analysis for 10 displayed a conformer possessing a P(M) bowl chirality and a PPMPM (PMPMM) helical chirality, which was found to be the most stable conformer(s). Variable-temperature NMR measurements of 10 and 11 revealed that their structural isomers can be interconvertible in solution, depending on the steric congestion around the helical scaffolds. Automated search for conformers in the equilibrium and transition states by Artificial Force Induced Reaction (AFIR) method revealed their interconversion networks, including bowl-inversion and helical-inversion. This analysis indicated that the co-existing corannulene and azahelicene moieties influence the conformational dynamics, which leads to mitigation of the activation energy barriers for isomerization.

ON/OFF metal-triggered molecular tweezers for fullerene recognition

Herein, we report molecular tweezers for fullerene recognition based on 2,2'-bipyridine-bearing corannulene motifs. The syn or anti confirmation can be selected simply by Cu(I) coordination/decoordination, thus controlling the fullerene recognition capability of the system on demand and leading to the formation of effective metal-triggered ON/OFF molecular tweezers.

A Distorted Hybrid Corannulene-Dibenzobistetracene

We have designed and synthesized a new type of distorted nanographene by Diels-Alder and Scholl reactions that contains one dibenzobistetracene (DBT, 1) core and two end-capping corannulene units. Single-crystal X-ray diffraction analyses demonstrate that nanographene 1 contains two [5] helicene subunits with a dihedral angle of 62°, consequently leading to the distorted DBT core. In addition, the photophysical properties and (non)aromaticity of 1 were investigated by the absorption and emission spectra in combination with theoretical calculations.

Graphitic supramolecular architectures based on corannulene, fullerene, and beyond

In this Feature Article, we survey the advances made in the field of fulleretic materials over the last five years. Merging the intriguing characteristics of fulleretic molecules with hierarchical materials can lead to enhanced properties of the latter for applications in optoelectronic, biomaterial, and heterogeneous catalysis sectors. As there has been significant growth in the development of fullerene- and corannulene-containing materials, this article will focus on studies performed during the last five years exclusively, and highlight the recent trends in designing fulleretic compounds and understanding their properties, that has enriched the repertoire of carbon-rich functional materials.

Synthesis and Structural Elucidation of Bisdibenzocorannulene in Multiple Redox States

We report an anti-folded bowl-shaped bisdibenzocorannulene (BDBC) featuring a new chair-cyclohexane-like hexagon as a bridge of two dibenzocorannulene moieties. The neutral compound showed multiple redox-active properties and could be converted to the corresponding redox states through chemical reduction or oxidation. Chemical reduction of BDBC by stoichiometric addition of metallic potassium in the presence of [18]crown-6 ether, provided a radical anion BDBC^.- and a dianion BDBC^2- , respectively; while chemical oxidation by silver hexafluoroantimonate(V), converted the neutral compound to an open-shell singlet diradical dication (BDBC^.. )²⁺ . The structural consequences of both electron-reduction and oxidation were closely related to the release of ring-strain of the bowl-shaped π-scaffold and imposed steric hindrance of the hexagonal bridge. In addition, the unusual open-shell nature of the dication could mainly be attributed to the changing of localized antiaromaticity in the closed-shell structure to delocalized character in the biradical, and thus the emergence of weakly bonded π-electrons.

In silico design to enhance the barrier height for magnetization reversal in Dy(iii) sandwich complexes by stitching them under the umbrella of corannulene

Lanthanide based single molecular magnets (SMMs), particularly dysprocenium based SIMs, are well known for their high energy barrier for spin reversal (U eff) and blocking temperatures (T B). Enhancing these two parameters and at the same time obtaining ambient stability is key to realising end-user applications such as compact storage or as qubits in quantum computing. In this work, by employing an array of theoretical tools (DFT, ab initio CASSCF and molecular dynamics), we have modelled six complexes [(η5-corannulene)Dy(Cp)] (1), [(η5-corannulene)Dy(C6H6)] (2), [(η6-corannulene)Dy(Cp)] (3), [(η6-corannulene)Dy(C6H6)] (4), [(exo-η5-corannulene)Dy(endo-η5-corannulene)] (5), and [(endo-η5-corannulene)Dy(endo-η5-corannulene)] (6) containing corannulene as a capping ligand to stabilise Dy(iii) half-sandwich complexes. Our calculations predict a strong axiality exerted by the Dy-C interactions in all complexes. Ab initio calculations predict a very large barrier height for all six molecules in the order 1 (919 cm-1) ≈ 3 (913 cm-1) > 2 (847 cm-1) > 4 (608 cm-1) ≈ 5 (603 cm-1) ≈ 6 (599 cm-1), suggesting larger barrier heights for Cp ring systems, followed by six-membered arene systems and then corannulene. DFT based molecular dynamics calculations were performed on complexes 3, 5 and 6. For complexes 3 and 5, the geometries that are dynamically accessible are far fewer. The range of U eff computed for molecular dynamics snapshots is high, indicating a possibility of translating the large U eff obtained into attractive blocking temperatures in these complexes, but the converse is found for 6. Furthermore, an in-depth C-H bond vibrational analysis performed on complex 3 suggests that the vibration responsible for reducing the blocking temperature in dysprocenium SIMs is absent here as the C-H bonds are stronger and corannulene steric strain prevents the C(Cp)-Dy-C(Cor) bending. As [(η6-corannulene)TM(X)]+ (TM = Ru, Zr, Os, Rh, Ir and X = C5Me5, C6Me6) are known, the predictions made here have a higher prospect of yielding stability under ambient conditions, a very large U eff value and a high blocking temperature - a life-giving combination to new generation SMMs.

Mechanochemical transformation of planar polyarenes to curved fused-ring systems

The transformation of planar aromatic molecules into π-extended non-planar structures is a challenging task and has not been realized by mechanochemistry before. Here we report that mechanochemical forces can successfully transform a planar polyarene into a curved geometry by creating new C-C bonds along the rim of the molecular structure. In doing so, mechanochemistry does not require inert conditions or organic solvents and provide better yields within shorter reaction times. This is illustrated in a 20-minute synthesis of corannulene, a fragment of fullerene C60, in 66% yield through ball milling of planar tetrabromomethylfluoranthene precursor under ambient conditions. Traditional solution and gas-phase synthetic pathways do not compete with the practicality and efficiency offered by the mechanochemical synthesis, which now opens up a new reaction space for inducing curvature at a molecular level.

A palate of fluorescent corannulene derivatives: synthesis, spectroscopic properties, and bio-imaging application

Reported here is a palate of fluorescent corannulene derivatives suitable for cellular imaging. They are derived from "tagging" corannulene with known fluorophores. The tagged corannulenes display strong fluorescence (φF > 0.25 in MeOH), good photostability and long emission wavelength (500 nm to 600 nm). Cell staining experiments indicate that several of them have excellent cell membrane permeability and targeting ability. In addition, we have found an unexpected, highly efficient energy transfer from corannulene to the pendant fluorophore. This has implications for many areas of corannulene research.

Corannulene: A Curved Polyarene Building Block for the Construction of Functional Materials

This Account describes a body of research in the design and synthesis of molecular materials prepared from corannulene. Corannulene (C₂₀H₁₀) is a molecular bowl of carbon that can be visualized as the hydrogen-terminated cap of buckminsterfullerene. Due to this structural resemblance, it is often referred to as a buckybowl. The bowl can invert, accept electrons, and form host-guest complexes. Due to these characteristics, corannulene presents a useful building block in materials chemistry.In macromolecular science, for example, assembly of amphiphilic copolymers carrying a hydrophobic corannulene block enables micelle formation in water. Such micellar nanostructures can host large amounts of fullerenes (C₆₀ and C₇₀) in their corannulene-rich core through complementarity of the curved π-surfaces. Covalent stabilization of the assembled structures then leads to the formation of robust water-soluble fullerene nanoparticles. Alternatively, use of corannulene in a polymer backbone allows for the preparation of electronic and redox-active materials. Finally, a corannulene core enables polymer chains to respond to solution temperature changes and form macroscopic fibrillar structures. In this way, the corannulene motif brings a variety of properties to the polymeric materials.In the design of non-fullerene electron acceptors, corannulene is emerging as a promising aromatic scaffold. In this regard, placement of sulfur atoms along the rim can cause an anodic shift in the molecular reduction potential. Oxidation of the sulfur atoms can further enhance this shift. Thus, a variation in the number, placement, and oxidation state of the sulfur atoms can create electron acceptors of tunable and high strengths. An advantage of this molecular design is that material solubility can also be tuned. For example, water-soluble electron acceptors can be created and are shown to improve the moisture resistance of perovskite solar cells.Host-guest complexation between corannulene and γ-cyclodextrin under flow conditions of a microfluidic chamber allows for the preparation of water-soluble nanoparticles. Due to an oligosaccharide-based sugarcoat, the nanoparticles are biocompatible while the corannulene component renders them active toward nonlinear absorption and emission properties. Together, these attributes allow the nanoparticles to be used as two-photon imaging probes in cancer cells.Finally, aromatic extension of the corannulene nucleus is seen as a potential route to nonplanar nanographenes. Typically, such endeavors rely upon gas-phase synthesis or metal-catalyzed coupling protocols. Recently, two new approaches have been established in this regard. Photochemically induced oxidative cyclization, the Mallory reaction, is shown to be a general method to access corannulenes with an extended π-framework. Alternatively, solid-state ball milling can achieve this goal in a highly efficient manner. These new protocols bring practicality and sustainability to the rapidly growing area of corannulene-based nanographenes.In essence, corannulene presents a unique building block in the construction of functional materials. In this Account, we trace our own efforts in the field and point toward the challenges and future prospects of this area of research.

Ion Mobility Mass Spectrometry Uncovers Guest-Induced Distortions in a Supramolecular Organometallic Metallosquare

The encapsulation of the tetracationic palladium metallosquare with four pyrene-bis-imidazolylidene ligands [1]4+ with a series of organic molecules was studied by Electrospray ionization Travelling Wave Ion-Mobility Mass Spectrometry (ESI TWIM-MS). The method allowed to determine the Collision Cross Sections (CCSs), which were used to assess the size changes experienced by the host upon encapsulation of the guest molecules. When fullerenes were used as guests, the host is expanded ΔCCS 13 Å2 and 23 Å2 , for C60 or C70 , respectively. The metallorectangle [1]4+ was also used for the encapsulation of a series of polycyclic aromatic hydrocarbons (PAHs) and naphthalenetetracarboxylic diimide (NTCDI), to form complexes of formula [(NTCDI)2 (PAH)@1]4+ . For these host:guest adducts, the ESI IM-MS studies revealed that [1]4+ is expanded by 47-49 Å2 .. The energy-minimized structures of [1]4+ , [C60 @1]4+ , [C70 @1]4+ , [(NTCDI)2 (corannulene)@1]4+ in the gas phase were obtained by DFT calculations.Introduction.

Bowl-Shaped Pentagon- and Heptagon-Embedded Nanographene Containing a Central Pyrrolo[3,2-b]pyrrole Core

A bowl-shaped nitrogen-doped nanographene composed of a pyrrolo[3,2-b]pyrrole core substituted with six arene rings circularly bonded with one another has been prepared via a concise synthetic strategy encompassing the multicomponent tetraarylpyrrolopyrrole (TAPP) synthesis, the Scholl reaction, and intramolecular direct arylation. This synthesis represents the first case of programmed sequential intramolecular direct arylation reactions utilizing the different reactivity of C-Br and C-Cl bonds. The target compound contains two central pentagons confined between two adjacent heptagons-the inverse Stone-Thrower-Wales topology. The presence of both five- and seven-membered rings in the final structure is responsible for interesting properties such as a perpendicularly aligned dipole moment, absorption and fluorescence in the orange-red region, weak emission originating from the charge-transfer character of a low-energy absorption band, and a high lying HOMO. In the solid state slipped convex-to-convex π-π stacking dominates.