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.

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.

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.

Thermodynamic Differentiation of the Two Sides of Azabuckybowl through Complexation with Square Planar Platinum(II)

The precise control of the two faces, concave/convex faces, is an attractive challenge to realizing novel dynamic molecular systems. Herein, we report the synthesis, X-ray crystal structure, and bowl-to-bowl inversion behavior of a platinum complex with azabuckybowl as a monodentate ligand. X-ray crystallography revealed that the azabuckybowl is orthogonally coordinated to the plane containing the Pt center and other ligands. One and two-dimensional NMR studies have also confirmed that this complex was observed as mixtures of two isomers, although the isomeric ratio was highly biased. Theoretical calculations indicate that the difference in thermodynamic stability of these isomers is due to the direction of the concave/convex face of an azabuckybowl ligand.

Recent Advances in Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds

This review surveys recent progress in the chemistry of polycyclic heteroaromatic molecules with a focus on structural diversity and synthetic methodology. The article covers literature published during the period of 2016-2020, providing an update to our first review of this topic (Chem. Rev. 2017, 117 (4), 3479-3716).

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.

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.

Theoretical study on the molecular stacking interactions and charge transport properties of triazasumanene crystals - from explanation to prediction

Computational analyses of the solid-state properties of triazasumanene (TAS), a C₃-symmetric nitrogen-doped sumanene derivative, were carried out in this work. The present studies are mainly divided into two parts. In the first part, we demonstrated the differences in the interactions of the crystal packing between the racemic and the homochiral structures: the former having perpendicular columnar packing and the latter forming slipped helical packing. Two geometries of the TAS monomer, a theoretically optimized structure under vacuum and an X-ray crystal structure in experiment, were compared. It can be found that it is not the total interaction energy, but the local interactions (mainly the electrostatic interactions) of the molecular dimer that dominate the columnar stacking conformation. The second part involves the investigation of the potential charge transport properties of the crystals according to the semiclassical Marcus theory with the hopping mechanism using the simple dimer model. The charge transfer integrals of the two sets of dimers, racemic and homochiral dimer models, were compared as well. The calculation results show that the TAS racemic crystal was predicted to have an advantage of hole transport properties. The perpendicular columnar stacking of the homochiral conformation should essentially have better charge transport properties than the racemic conformation. It is reasonable to employ the simple dimer model built using optimized monomers under vacuum for the purpose of the prediction of the molecular packing conformation by IES calculation and the charge transport properties of the perpendicular columnar-stacking crystal. Our work provides a simple approach to the deep understanding of the structure-property relationship of bowl-shaped molecular systems in theory. It can help to facilitate the design and preparation of heteroatom-doped sumanene derivatives with perpendicular columnar stacking crystals as novel organic semiconductor materials.

A Design Principle for Polar Assemblies with C3 -Sym Bowl-Shaped π-Conjugated Molecules

Polar materials attract wide research interest due to their unique properties, such as ferroelectricity and the bulk photovoltaic effect (BPVE), which are not accessible with nonpolar materials. However, in general, rationally designing polar materials is difficult because nonpolar materials are more favorable in terms of dipole-dipole interactions. Here, we report a rational strategy to form polar assemblies with bowl-shaped π-conjugated molecules and a molecular design principle for this strategy. We synthesized and thoroughly characterized 12 single crystals with the help of various theoretical calculations. Furthermore, we demonstrated that it can be possible to predict whether polar assemblies become more favorable or not by estimating their lattice energies. We believe that this study contributes to the development of organic polar materials and their related studies.

Effect of Fusion Manner of Concave Molecules on the Properties of Resulting Nanoboats

A boat-shaped compound, which can be viewed as the fusion of two concave molecules with crossed quinacridone and indolocarbazole throughout, was synthesized and characterized. The investigation determined that the fusion manner of two concave molecules has little influence on the molecular curvature and aromaticity when compared with its congener containing crossed indolocarbazole throughout. The situation of carbonyl groups is critical in adjusting the electronic structure and physicochemical properties due to the fixed position of nitrogen atoms.

Modulating the properties of buckybowls containing multiple heteroatoms

Nitrogen-centered buckybowls with sulfur decoration at the rim were synthesized and characterized. The buckybowls demonstrate tunable properties depending on the state of the sulfur atom.

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.

An Isosteric Triaza Analogue of a Polycyclic Aromatic Hydrocarbon Monkey Saddle

Since a few years, the interest in negatively-curved fused polycyclic aromatic hydrocarbons (PAHs) has significantly increased. Recently, the first chiral negatively-curved PAH with the topology of a monkey saddle was introduced. Herein the synthesis of its triaza congener is reported. The influence of this CH↔N exchange on photophysical and electrochemical properties is studied as well as the isomerization process of the enantiomers. The aza analogue has a significantly higher inversion barrier, which makes it easier to handle at room temperature. All experimental results are underpinned by theoretical DFT calculations.

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.

Time-Dependent Density Functional Theory Investigation of Excited State Intramolecular Proton Transfer in Tris(2-hydroxyphenyl)triazasumanene

Previously, our group reported dual-emission spectra for tris(2-hydroxyphenyl)triazasumanene (OHPhTAS), comprising three OH···N-type intramolecular hydrogen bonds from three phenolic rings connected to the nitrogen-doped buckybowl skeleton, corresponding to the excited state intramolecular proton transfer (ESIPT) in the solid state. However, the dual emission is not observed in a nonpolar solution. In this study, the mechanism and multiplicity of potentially photoinduced dynamic ESIPT were investigated both in ground (S₀) and in excited states (S₁) by time-dependent density functional theory calculations. Different pathways, concerted and stepwise (single, double, or triple) PT processes, are considered. The calculated vertical emission energies (S₁ → S₀ states) and adiabatic total energies at S₀ and S₁ states of OHPhTAS and its tautomers revealed that a single PT, trienol (EEE) → monoketo (KEE), is the main contribution in OHPhTAS with an ultrasmall PT energy barrier. The nonradiative decay of OHPhTAS was analyzed by the potential energy curve (PEC) at the S₁ state along EEE* to KEE*. The results indicated that nonradiative decay was prohibited in the solid state but significantly stabilized in nonpolar solutions. The nonradiative routes in the solution state were confirmed by the minimum energy crossing point of the T₁/S₀ pathway, wherein the dihedral angle φ between the phenolic ring and pyridine moiety on the buckybowl structure relaxed to 123°.

Application of cup-shaped trilactams for selective extraction of volatile compounds by gas chromatography-mass spectrometry

Chiral cup-shaped trilactams were used as liquid phase extraction material of volatile organic compounds in perfume analyzed by SPME GC-MS. (+)-material showed higher selective chiral recognition with oxygenated and cyclic volatile compounds.

Synthesis of Tellurium-Containing π-Extended Aromatics with Room-Temperature Phosphorescence

A synthesis of tellurium-embedded π-extended aromatics from tellurium powder and readily available cyclic diaryliodonium salts has been developed. The versatility of this method has been demonstrated by the synthesis of various functionalized dibenzotellurophenes (DBTe's), a ladder-type π-system, and a heterosumanene. These compounds demonstrated good air/moisture stability and high thermal stability. Remarkably, many DBTe's exhibited interesting tunable room-temperature phosphorescence (RTP) in the solid state.