Redox-Dependent Transformation of a Hydrazinobuckybowl between Curved and Planar Geometries

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 of a π-Extended Azacorannulenophane Enabled by Strain-Induced 1,3-Dipolar Cycloaddition

The first example of a cyclophane bearing a nitrogen-containing buckybowl was synthesized via sequential 1,3-dipolar cycloaddition and palladium-catalyzed intramolecular cyclization. The key to the successful synthesis is the strain-induced 1,3-dipolar cycloaddition of a polycyclic aromatic azomethine ylide to the K-region of [7](2,7)pyrenophane. The resulting π-extended azacorannulenophane exhibits intriguing structural and physical properties, including unique variation of bowl depth, extraordinarily high-field chemical shifts in its ¹ H NMR spectrum, a decreased HOMO-LUMO gap, and a red shift in the absorption/emission spectrum, when compared to those of the parent azacorannulene. These characteristics are derived from both the π-extension to the polycyclic aromatic system in the cyclophane structure and the increased curvature enforced by the seven-carbon aliphatic chain.

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.

Electrochemical Heteroatom-Heteroatom Bond Construction

Heteroatom-heteroatom linkage, with S-S bond as a presentative motif, served a crucial role in biochemicals, pharmaceuticals, pesticides, and material sciences. Thus, preparation of the privileged scaffold has always been attracting tremendous attention from the synthetic community. However, classic protocols suffered from several drawbacks, such as toxic and unstable agents, poor functional group tolerance, multiple steps, and explosive oxidizing regents as well as the transitional metal catalysts. Electrochemical organic synthesis exhibited a promising alternative to the traditional chemical reaction due to the sustainable electricity can be employed as the traceless redox agents. Hence, toxic and explosive oxidants and/or transitional metals could be discarded under mild reaction with high efficiency. In this context, a series of electrochemical approaches for the construction of heteroatom-heteroatom bond were reviewed. Notably, most of the cases illustrated the dehydrogenative feature with the clean energy molecules hydrogen as the sole by-product.

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.

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.

A Nanoboat with Fused Concave N-Heterotriangulene

The surface extension of all-carbon based bowl-shaped molecules, such as corannulene and sumanene, to synthesize even larger buckybowls has been widely studied, leaving other concave compounds with heteroatoms less considered. Herein we present a highly curved molecule synthesized via stepwise cyclization of fjords of a bisacridone derivative. Crystallographic analysis unambiguously confirmed a boat-shaped structure with deformed bottom benzene ring. Theoretical calculation unravels an inversion process with an S-shaped transition structure rather than a planar one. The enlarged boat demonstrates interesting properties, such as red shifts in absorption and emission spectra, enhanced emission intensity, and convergent frontier molecular orbital energy levels, in comparison to the related concave N-heterotriangulene.

Polycyclic Aromatic Hydrocarbons Containing A Pyrrolopyridazine Core

Polycyclic aromatic azomethine ylides (PAMYs) are versatile building blocks for the bottom-up construction of unprecedented nitrogen-containing polycyclic aromatic hydrocarbons (N-PAHs). Here, we demonstrate the 1,3-dipolar cycloaddition between PAMY and 1,4-diphenylbut-2-yne-1,4-dione and the subsequent condensation reaction with hydrazine, which led to unique N-PAHs with a phenyl-substituted pyrrolopyridazine core (PP-1 and PP-2). The molecular structures of pristine PP-1 and tert-butyl-substituted PP-2 were verified by NMR spectroscopy and mass spectrometry. Moreover, the structure of PP-2 was unambiguously elucidated by X-ray single crystal analysis. The optoelectronic properties were investigated by solvent-dependent UV-Vis absorption and fluorescence emission spectroscopy as well as cyclic voltammetry. Additionally, density functional theory (DFT) calculations showed that PP-1 and PP-2 exhibit push-pull behavior. Furthermore, in situ EPR/UV-Vis-NIR spectroelectrochemistry allowed the detailed insight into the spectroscopic properties and spin distribution of radical cation species of PP-2.

Non-Planar [n]Cyclo-1,8-carbazolylenes (n=3,4,6) and [3]Cyclo-1,8-carbazolylenyl B, P, PO, SiPh Complexes

A new family of non-planar heterocyclic molecules consisting of carbazoles was created. A bowl-shaped cyclodimer, a flake-shaped cyclotrimer, a double-decker-ring-shaped cyclotetramer and a cyclohexamer were synthesized by Ni⁰ -mediated one-shot cyclo-oligomerization of 1,8-dibromocarbazole, and were named [n]cyclo-1,8-carbazolylenes (n=3,4,6). [3]Cyclo-1,8-carbazolylene was found to act as a trivalent tridentate ligand for heteroatoms (B, P, Si), giving flake-shaped complexes. The boron derivative acted as a Lewis acid, and the tetra-coordinated complexes showed an unprecedented red-shift of absorption and emission spectra by the coordination. The synthetic method, the distorted C₂ or C₁ symmetric shape, the trivalent tridentate coordination ability and the kinds of introduced heteroatoms of [3]cyclo-1,8-carbazolylenes, the electronic structure, the photophysical property, and the Lewis acidity were distinct from those of related subporphyrins/subphthalocyanines.