Formation of a Large Confined Spherical Space with a Small Aperture Using Flexible Hexasubstituted Sumanene

Synthesis, Structures, and Properties for PIII-Doped Hetero-Buckybowls and Their Phosphonium Salts

Doping polycyclic aromatic hydrocarbons with heteroatoms enables manipulation of their electronic structures. Herein, the structures and properties of phosphorus (P) doped heterosumanenes (HSEs) are regulated by varying the valence states of P-dopant. The phosphine sulfide (PV) and chalcogens (S, Se, Te) co-doped HSEs (1-3) are reduced to trivalent phosphorus (PIII) doped analogues 4-6. Then, the PIII-dopants on 4-6 are converted to phosphonium salts (R4P+), giving 7-9. The valence states of P-dopant show great influence on molecular geometries and electronic structures. Taking P and S co-doped HSEs as example, bowl-depths increase in the order of 1 (PV)<7 (R4P+)<4 (PIII), and the HOMO energy levels and HOMO-LUMO gaps increase to be 7<1<4. Consistent with the theoretical calculation, the first oxidation potentials decrease and the absorption/emission bands show blue shift from 7 to 1 to 4. The transformation of PV to PIII leads to large variations on the coordination with Ag+, owing to the alteration of coordination site from P=S to PIII. The phosphonium salts show ring-opening of phosphole rings under electrochemical reduction. It is found that chalcogen atoms play pivotal roles on coordination patterns of coordination complexes and the conversion rates of ring-opening reactions.

Coordination complexes of PIII-doped heterobuckybowls and their applications in catalysis

Doping the π-frameworks of polycyclic aromatic hydrocarbons (PAHs) with main-group elements is a powerful strategy to manipulate optoelectronic properties. Herein, the benzylic carbons of π-bowl sumanene are replaced with chalcogens (S, Se, and Te) and trivalent phosphorus (PIII), affording a series of PIII-doped heterosumanenes (HSEs). The lone-pair electrons of the PIII-dopant endow these HSEs with pronounced affinity toward transition metals (Au+, Pt2+, and Pd2+). Accordingly, nine coordination complexes were synthesized to exhibit diverse coordination patterns contingent upon the metal ions and chalcogen atoms on HSEs. For the first time, we proved that the Pd2+ complexes of these HSEs are promising catalysts for the Suzuki-Miyaura coupling reaction of aryl chlorides.

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.

Symmetric Aromatic Amidoalkylations of Triphenylenes

Triphenylene derivatives are highly investigated for their electronic, supramolecular and photophysical properties, but the direct modification of the central aromatic core is particularly challenging especially in the internal positions 1, 4, 5, 8, 9, and 12. Herein we present an efficient alkylation method of 2,3,6,7,10,11-hexasubstituted triphenylene derivatives leading to tris-alkylated C3-symmetric derivatives in good yields using N-(hydroxymethyl)carboxamide or N-(alkoxylmethyl)carboxamide alkylating agents.

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.

Radical Cation Salts of Hetera-Buckybowls: Polar Crystals, Negative Thermal Expansion and Phase Transition

Radical cation salts of π-conjugated polycycles are rich in physical properties. Herein, two kinds of hetera-buckybowls, ethoxy-substituted trithiasumanene (3SEt) and triselenasumanene (3SeEt), are synthesized as electron donors. Galvanostatic oxidation of them affords radical cation salts (3SEt)5 (TTFMPB)3 , (3SeEt)5 (TTFMPB)3 , (3SEt)4 PMA, and (3SeEt)4 PMA, where PMA is Keggin-type phosphomolybdate and TTFMPB is tetrakis[3,5-bis(trifluoromethyl)-phenyl]borate. In these salts, 3SEt/3SeEt are partially charged and show distinct conformation change with the site charge and counter anions. In TTFMPB salts, (TTFMPB)- forms hexagonal channels that accommodate the packing columns of 3SEt/3SeEt. In particular, (3SEt)5 (TTFMPB)3 adopts the R3c space group and is a polar crystal with the columns of 3SEt all in the up-bowl direction. The PMA salts of 3SEt/3SeEt are polar crystals (C2 space group) with 3SEt/3SeEt being planar and forming columnar stacks. (3SeEt)4 PMA shows a structural modulation below 200 K, namely, negative thermal expansion (NTE) of the unit cell volume and enlargement of the intermolecular distances between neighboring 3SeEt molecules. The four salts are semiconductors with an activation energy of 0.18-0.38 eV. The conductivity of (3SeEt)4 PMA shows a reversible transition upon cooling and heating, in accordance to the NTE structural modulation. This work paves the way toward conducting materials based on hetera-buckybowls.

Oxidation-derived anticancer potential of sumanene-ferrocene conjugates

An effective synthetic protocol towards the oxidation of sumanene-ferrocene conjugates bearing one to four ferrocene moieties has been established. The oxidation protocol was based on the transformation of FeII from ferrocene to FeIII-containing ferrocenium cations by means of the treatment of the title organometallic buckybowls with a mild oxidant. Successful isolation of these ferrocenium-tethered sumanene derivatives 5-7 gave rise to the biological evaluation of the first, buckybowl-based anticancer agents, as elucidated by in vitro assays with human breast adenocarcinoma cells (MDA-MB-231) and embryotoxicity trials in zebrafish embryos supported with in silico toxicology studies. The designed ferrocenium-tethered sumanene derivatives featured attractive properties in terms of their use in cancer treatments in humans. The tetra-ferrocenium sumanene derivative 7 featured especially beneficial biological features, elucidated by low (<40% for 10 μM) viabilities of MDA-MB-231 cancer cells together with a 1.4-1.7-fold higher viability of normal cells (human mammary fibroblasts, HMF) for respective concentrations. Compound 7 featured significant cytotoxicity against cancer cells thanks to the presence of sumanene and ferrocenium moieties; the latter motif also provided the selectivity of anticancer action. The biological properties of 7 were also improved in comparison with those of native building blocks, which suggested the effects of the presence of the sumanene skeleton towards the anticancer action of this molecule. Ferrocenium-tethered sumanene derivatives exhibited potential towards the generation of reactive oxygen species (ROS), responsible for biological damage to the cancer cells, with the most efficient generation of the tetra-ferrocenium sumanene derivative 7. Derivative 7 also did not show any embryotoxicity in zebrafish embryos at the tested concentrations, which supports its potential as an effective and cancer-specific anticancer agent. In silico computational analysis also showed no chromosomal aberrations and no mutation with AMES tests for the compound 7 tested with and without microsomal rat liver fractions, which supports its further use as a potent drug candidate in detailed anticancer studies.

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.

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.

Synthesis and derivatization of hetera-buckybowls

Buckybowls have concave and convex surfaces with distinct π-electron cloud distribution, and consequently they show unique structural and electronic features as compared to planar aromatic polycycles. Doping the π-framework of buckybowls with heteroatoms is an efficient scheme to tailor inherent properties, because the nature of heteroatoms plays a pivotal role in the structural and electronic characteristics of the resulting hetera-buckybowls. The design, synthesis, and derivatization of hetera-buckybowls open an avenue for obtaining fascinating organic entities not only of fundamental importance but also of promising applications in optoelectronics. In this review, we summarize the advances in hetera-buckybowl chemistry, particularly the synthetic strategies toward these scaffolds.

Disaggregation of a sumanene-containing fluorescent probe towards highly sensitive and specific detection of caesium cations

A sumanene derivative functionalized with triphenylbenzene units was found to exhibit aggregation-induced emission enhancement (AIEE). A disaggregation process after the addition of caesium cations (Cs+) was observed. This feature was employed for the design of the first sumanene-containing disaggregation-based fluorescent probe for specific, efficient and fast Cs+ recognition.

Transforming electron-rich hetero-buckybowls into electron-deficient polycycles

Oxidation of trichalcogenasumanenes (TCSs) with NO species results in the simultaneous formation of ortho-quinone and diester groups. This reaction enables the transformation of electron-rich TCSs into electron-deficient polycycles.

Synthetic approaches to bowl-shaped π-conjugated sumanene and its congeners

Since the first synthetic report in 2003 by Sakurai et al., sumanene (derived from the Indian 'Hindi as well as Sanskrit word' "Suman", which means "Sunflower"), a beautifully simple yet much effective bowl-shaped C 3-symmetric polycyclic aromatic hydrocarbon having three benzylic positions clipped between three phenyl rings in the triphenylene framework has attracted a tremendous attention of researchers worldwide. Therefore, since its first successful synthesis, a variety of functionalized sumanenes as well as heterosumanenes have been developed because of their unique physiochemical properties. For example, bowl-to-bowl inversion, bowl depth, facial selectivity, crystal packing, metal complexes, intermolecular charge transfer systems, cation-π complexation, electron conductivity, optical properties and so on. Keeping the importance of this beautiful scaffold in mind, we compiled all the synthetic routes available for the construction of sumanene and its heteroatom derivatives including Mehta's first unsuccessful effort up to the latest achievements. Our major goal to write this review article was to provide a quick summary of where the field has been, where it stands at present, and where it might be going in near future. Although several reviews have been published on sumanene chemistry dealing with different aspects but this is the first report that comprehensively describes the 'all-in-one' chemistry of the sumanene architecture since its invention to till date. We feel that this attractive review article will definitely help the scientific community working not only in the area of organic synthesis but also in materials science and technology.

A ferrocene-templated Pd-bearing molecular reactor

High-yield, chromatography-free syntheses of a ferrocene-templated molecular cage and its Pd-bearing derivative are presented. The formation of a symmetric cage-type structure was confirmed by single-crystal X-ray diffraction analysis. The Pd-bearing cage was used as an innovative catalyst for the efficient synthesis of 1,1'-biphenyls under mild conditions. The presented catalyst is reusable and 1,1'-biphenyls can be obtained efficiently in a gram scale process.

Hydrogen-bonded porous frameworks constructed by rigid π-conjugated molecules with carboxy groups

This review covers construction and properties of porous molecular crystals (PMCs) constructed through hydrogen-bonding of C3-symmetric, rigid, π-conjugated molecular building blocks possessing carboxyaryl groups, which was reported in the last 5 years by the author’s group. PMCs with well-defined, self-standing pores have been attracted attention due to various functionalities provided by selective and reversible inclusion of certain chemical species into the pores. However, it has been recognized for long time that construction of PMCs with permanent porosity is not easy due to weakness of noncovalent intermolecular interactions. Systematic construction of PMCs have been limited so far. To overcome this problem, the author has proposed a unique molecular design concept based on C3-symmetric π-conjugated molecules (C3PIs) possessing o-bis(4-carboxyphenyl)benzene moieties in their periphery and demonstrated that C3PIs systematically yielded hydrogen-bonded organic frameworks (HOFs) composed of H-bonded 2D hexagonal networks (H-HexNets) or interpenetrated 3D pcu-networks, which exhibit permanent porosity, significant thermal stability, polar solvent durability, robustness/flexibility, and/or multifunctionality.