Youzhi

Herein, we report on the synthesis of a novel π-extended "superhelicene" based on hexa-peri-hexabenzocoronenes (HBC) via an efficient four-step synthetic procedure starting from diphenylether. Comprehensive structural analyses were performed by means of NMR and mass spectrometry measurements together with X-ray analysis. Physico-chemical analysis of the superhelicene and suitable HBC references revealed among others outstanding fluorescent features with quantum yields of over 80%.

Abstract: A synthetic protocol for the synthesis of 3D hexakisimidazolium cage compounds has been developed. Reaction of trigonal trisimidazolium salts H3L decorated with three N-olefinic pendants and silver oxide yielded trinuclear trisilver(I) hexacarbene molecular cylinders of type [Ag3L2]3+ with the olefinic pendants from the two different tricarbene ligands arranged in three pairs. Subsequent UV-irradiation gave via three [2+2]-cycloaddition reactions three cyclobutane links between the two tris-NHC ligands thereby generating a three-dimensional hexakis-NHC ligand. Subsequent removal of the metal ions resulted in the formation of three-dimensional hexakisimidazolium cages with a large internal cavity constituting the first examples for such compounds.

Despite significant progress in the synthesis of covalent organic frameworks (COFs), reports on the precise construction of template-free nano- and microstructures of such materials have been rare. In the quest for dye-containing porous materials, a novel conjugated framework DPP-TAPP-COF with an enhanced absorption capability up to λ=800 nm has been synthesized by utilizing reversible imine condensations between 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TAPP) and a diketopyrrolopyrrole (DPP) dialdehyde derivative. Surprisingly, the obtained COF exhibited spontaneous aggregation into hollow microtubular assemblies with outer and inner tube diameters of around 300 and 90 nm, respectively. A detailed mechanistic investigation revealed the time-dependent transformation of initial sheet-like agglomerates into the tubular microstructures.

Rolling up the COFs: Tetraphenylporphyrins and diketopyrrolopyrroles have been incorporated as functional dye components in covalent organic frameworks by means of reversible imine condensations. Upon formation, these crystalline polymers spontaneously self-assemble to form hollow microtubes.

Herein, we report the design and synthesis of a series of novel cationic nitrogen-doped nanographenes (CNDNs) with nonplanar geometry and axial chirality. Single-crystal X-ray analysis reveals helical and cove-edged structures. Compared to their all-carbon analogues, the frontier orbitals of the CNDNs are energetically lower lying, with a reduced optical energy gap and greater electron-accepting behavior. Cyclic voltammetry shows all the derivatives to undergo quasireversible reductions. In situ spectroelectrochemical studies prove that, depending on the number of nitrogen dopants, either neutral radicals (one nitrogen dopant) or radical cations (two nitrogen dopants) are formed upon reduction. The concept of cationic nitrogen doping and introducing helicity into nanographenes paves the way for the design and synthesis of expanded nanographenes or even graphene nanoribbons with cationic nitrogen dopants.

Nitrogen plus: A new bottom-up synthetic method allows the generation of cationic nitrogen-doped nanographenes with nonplanar helical structures. The new nanographenes have interesting properties and have potential use as optical and electronic materials.

We demonstrate the transformation of oligofurans through sequential Diels–Alder cycloaddition reactions to provide oligoarenes in two chemical steps, regardless of the oligomer length. By this method, oligonaphthalenes containing up to six units were obtained in high yield through the formation of up to 12 new C−C bonds. The versatility of this method was demonstrated for various polyaromatic hydrocarbons. The regioselectivity of this process enabled the synthesis of a library of substituted triarylenes from a single terfuran precursor by modification of the dienophile strength and the order of addition. Overall, this study demonstrates that long oligofurans are interesting not only as organic electronic materials, but also as starting materials for the formation of various conjugated systems.

To cut a long story short: Oligofurans underwent sequential Diels–Alder reactions to provide oligoarenes in two chemical steps, regardless of the oligomer length (see picture). Different maleimide and benzyne dienophiles were also used to construct a range of substituted oligoarenes from a single oligofuran precursor in a highly regioselective manner.

Arene-fused cyclooctatetraenes (COTs) possess unique structural and electronic properties that originate from their saddle-shaped π-conjugated architectures. Considerable attention has been paid to the transition-metal-mediated synthesis of these cyclic compounds; however, there have been limited achievements to date in the efficient construction of heteroarene-fused COTs. In this contribution, we report a novel Pd-catalyzed dehydrogenative cyclodimerization of biheteroarenes through four-fold C−H activation toward the synthesis of a series of heteroarene-fused COTs. A set of mechanistic investigations indicated the involvement of high-valent Pd species prior to the dimerization event in the catalytic cycle. The redox behavior of the obtained COTs is also described briefly.

Ring cycle: A Pd-catalyzed reaction for the construction of thiophene-fused COT frameworks through dehydrogenative cyclodimerization of 3,3′-bithiophenes (X=S, Y=CH) has been developed. The method is applicable to various heteroaromatic compounds, and enables the facile synthesis of “composite” arene-fused COTs. Mechanistic studies indicated the involvement of palladacycle intermediates, as well as high-valent Pd species in the catalytic cycle.