A New Generation of Sumanene-Based AIEgens for the Effective Recognition of Metal Cations in Solutions Containing 95 vol % of Water

In recent years, the application of sumanene derivatives for the optical detection of metal cations was demonstrated. Unfortunately, known sumanene-based receptors enable the detection process in purely organic solutions or in aqueous media containing not lower than 50 vol % of organic solvent. Designing easy-to-synthesize sumanene-based optical receptors able to effectively recognize metal cations in aqueous solutions containing a slight volume fraction of organic solvent remained an important and vital challenge. In this work, we show that water-insoluble sumanene receptors composed of only carbon and hydrogen atoms enable the effective detection of cesium (Cs+) or lithium (Li+) cations in solutions containing 95 vol % of water. Their key feature is related to the exhibition of an aggregation-induced emission (AIE) effect. We discovered that the designed sumanene receptors exhibit excellent detection parameters expressed by Stern-Volmer constant values at the level from 108 to 1010 M-1. This work also shows that by simple modification of the sumanene receptor structure, it is possible to drastically change its detection preference from large Cs+ cations to small Li+ cations. The highest sensitivity of the designed receptors was concluded for Na+ or Li+, depending on the receptor structure. This work opens new avenues in designing sumanene-based optical receptors.

Complexation by γ-cyclodextrin as a way of improving anticancer potential of sumanene

Biological applications of sumanene buckybowl molecule have been widely discussed over the years yet remain still unexplored experimentally. On the other hand, creating cyclodextrin-containing supramolecular assemblies was demonstrated to be a powerful tool in terms of designing effective systems for medicinal chemistry purposes. Here, we show that sumanene molecule exclusively forms 1:1 host-guest complexes with γ-cyclodextrin (γCD) or (2-hydroxypropyl)-γ-cyclodextrin (HP-γCD), as revealed by extensive spectroscopic studies supported with density functional theory (DFT) computations. Based on our preliminary biological studies, we discovered that the formation of such complexes resulted in the improvement of anticancer properties of sumanene, expressed by high cell viabilities in vitro of healthy human mammary fibroblasts (HMF) together with low viabilities of human breast adenocarcinoma cells (MDA-MB-231). Improved pharmacokinetic (ADME-Tox) properties for sumanene@γCD and sumanene@HP-γCD complexes in comparison to native sumanene were also supported by in sillico modeling studies. This work provides the method how to focus the cytotoxic action of sumanene toward cancer cells using supramolecular assembly strategy, paving the way to the further exploration of biological properties of sumanene-containing supramolecular systems with bioactive features and applications of this buckybowl in general.

exo-6b2-Methyl-Substituted Pentabenzocorannulene: Synthesis, Structural Analysis, and Properties

exo-6b2-Methyl-substituted pentabenzocorannulene (exo-PBC-Me) was synthesized by the palladium-catalyzed cyclization of 1,2,3-triaryl-1H-cyclopenta[l]phenanthrene. Its bowl-shaped geometry with an sp3 carbon atom in the backbone and a methyl group located at the convex (exo) face was verified by X-ray crystallography. According to DFT calculations, the observed conformer is energetically more favorable than the endo one by 39.9 kcal/mol. Compared to the nitrogen-doped analogs with intact π-conjugated backbones (see the main text), exo-PBC-Me displayed a deeper bowl depth (avg. 1.93 Å), redshifted and broader absorption (250-620 nm) and emission (from 585 to more than 850 nm) bands and a smaller optical HOMO-LUMO gap (2.01 eV). exo-PBC-Me formed polar crystals where all bowl-in-bowl stacking with close π ⋅ ⋅ ⋅ π contacts is arranged unidirectionally, providing the potential for applications as organic semiconductors and pyroelectric materials. This unusual structural feature, molecular packing, and properties are most likely associated with the assistance of the methyl group and the sp3 carbon atom in the backbone.

Sumanene-carbazole conjugate with push-pull structure and its chemoreceptor application

The first-of-its-kind tetra-substituted sumanene derivative, featuring the push-pull chromophore architecture, has been successfully designed. The inclusion of both strong electron-withdrawing (CF3) and electron-donating (carbazole) moieties in this buckybowl compound has enhanced the charge transfer characteristics of the molecule. This enhancement was supported by ultraviolet-visible (UV-Vis) and emission spectra analyses along with density functional theory (DFT) calculations. The application of the title sumanene-carbazole push-pull chromophore as a selective recognition material for cesium cations (Cs+) was also presented. The title compound exhibited effective and selective Cs+-trapping ability, characterized by a high apparent binding constant value (at the level of 105) and a low limit of detection (0.09-0.13 μM). Owing to the tuned optical properties of the title push-pull chromophore, this study marks the first time in sumanene-tethered chemoreceptor chemistry where efficient tracking of Cs+ binding was possible with both absorption and fluorescence spectroscopies. This work introduces a new approach toward tuning the structure of bowl-shaped optical chemoreceptors.

Supramolecular Chemistry of Sumanene

Sumanene is a buckybowl molecule that is continuously attracting the attention of the scientific community because of its unique geometrical and physicochemical properties. This Minireview systematically summarizes advances and considerations regarding the applied supramolecular chemistry of sumanene. This work highlights the major fields in which potential or real applications of sumanene molecule have been reported to date, such as the design of sumanene-containing functional supramolecular materials and architectures, sumanene-based drug-delivery systems, or sumanene-tethered ion-selective molecular receptors. An assessment of the current status in the applied supramolecular chemistry of sumanene is provided, together with an emphasis on the key advances being made. Discussion on those milestones that are still to be achieved within this emerging field is also provided.

Strain-induced carbon-carbon bond cleavage of bowl-shaped sumanenone

This study details a highly effective ring-opening reaction that involves acid-mediated carbon-carbon bond cleavage of the buckybowl, sumanenone. The reaction of the bowl-shaped sumanenone with AcOH and TfOH results in the formation of a planar carboxylic acid. The examination of reactivity in comparison to planar analogues, along with theoretical calculations, suggests that the release of curved strain is a crucial factor for the success of this reaction.

Collective bending motion of a two-dimensionally correlated bowl-stacked columnar liquid crystalline assembly under a shear force

Stacked teacups inspired the idea that columnar assemblies of stacked bowl-shaped molecules may exhibit a unique dynamic behavior, unlike usual assemblies of planar disc- and rod-shaped molecules. On the basis of the molecular design concept for creating higher-order discotic liquid crystals, found in our group, we synthesized a sumanene derivative with octyloxycarbonyl side chains. This molecule forms an ordered hexagonal columnar mesophase, but unexpectedly, the columnar assembly is very soft, similar to sugar syrup. It displays, upon application of a shear force on solid substrates, a flexible bending motion with continuous angle variations of bowl-stacked columns while preserving the two-dimensional hexagonal order. In general, alignment control of higher-order liquid crystals is difficult to achieve due to their high viscosity. The present system that brings together higher structural order and mechanical softness will spark interest in bowl-shaped molecules as a component for developing higher-order liquid crystals with unique mechanical and stimuli-responsive properties.

Application of Monoferrocenylsumanenes Derived from Sonogashira Cross-Coupling or Click Chemistry Reactions in Highly Sensitive and Selective Cesium Cation Electrochemical Sensors

This paper reports the synthesis and characterization of novel monoferrocenylsumanenes obtained by means of the Sonogashira cross-coupling or click chemistry reaction as well as their application in cesium cation electrochemical sensors. A new synthetic protocol based on Sonogashira cross-coupling was developed for the synthesis of monoferrocenylsumanene or ethynylsumanene. The click chemistry reaction was introduced to the sumanene chemistry through the synthesis of 1,2,3-triazole containing monoferrocenylsumanene. The designed synthetic methods for the modification of sumanene at the aromatic position proved to be efficient and proceeded under mild conditions. The synthesized sumanene derivatives were characterized by detailed spectroscopic analyses of the synthesized sumanene derivatives. The supramolecular interactions between cesium cations and the synthesized monoferrocenylsumanenes were spectroscopically and electrochemically investigated. Furthermore, the design of the highly selective and sensitive cesium cation fluorescence and electrochemical sensors comprising the synthesized monoferrocenylsumanenes as receptor compounds was analyzed. The tested cesium cation electrochemical sensors showed excellent limit of detection values in the range of 6.0-9.0 nM. In addition, the interactions between the synthesized monoferrocenylsumanenes and cesium cations were highly selective, which was confirmed by emission spectroscopy, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and cyclic voltammetry.

Synthesis of π-extended and bowl-shaped sumanene-ferrocene conjugates and their application in highly selective and sensitive cesium cations electrochemical sensors

Carbon-carbon bond formation, condensation or click chemistry reactions were used to synthesize novel bowl-shaped sumanene-ferrocene conjugates, along with the extended π-electron framework in good yields. For the first time, the present study uses sumanene derivatives tris-substituted at the benzylic positions as the materials to begin the study on the click chemistry or the metal-catalyzed coupling reactions, Suzuki-Miyaura or Sonogashira couplings. The synthesized conjugates exhibited the property of selective recognizing cesium cations. As a result, this led to the development of highly sensitive and selective fluorescent or electrochemical sensors dedicated to the recognition of cesium cations (Cs⁺) in water. We successfully designed the Cs⁺ electrochemical sensors, which exhibited an acceptable limit of detection (LOD) values at 0.05-0.38 μM. Spectrofluorimetry, voltammetry, and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) were used to perform the selectivity studies. The results revealed that the designed sensors are highly Cs⁺-selective. This work significantly contributes to the design of new methods of sumanene modification. It also provides further information on the electrochemical properties and innovative applications of metallocene-tethered sumanene derivatives.

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.

Synthesis of the C70 Fragment Buckybowl, Homosumanene, and Heterahomosumanenes via Ring-Expansion Reactions from Sumanenone

Bowl-shaped aromatic molecules, buckybowls, are attractive molecules because of the unique properties derived from their curved-π scaffolds. Doping heteroatoms into buckybowl frameworks is a powerful method to change their structural and electronical properties. Herein, we report the synthesis of C₇₀ fragment buckybowl, homosumanene, and heterahomosumanenes having a lactone moiety and a lactam moiety via three ring-expansion reactions using sumanenone as a common intermediate. X-ray diffraction analysis of the single crystals reveals their columnar packing structure with a shallow bowl-depth. The lactam moiety is readily derivatized to give azahomosumanene derivatives, nitrogen-doped analogues of homosumanene possessing a pyridine ring at the peripheral carbon. The synthetic application of the α-phenyl azahomosumanene as a cyclometalating ligand with platinum also revealed its utility for preparing a metal complex bearing a buckybowl ligand.