Helically twisted nanoribbons via stereospecific annulative π-extension reaction employing [7]helicene as a molecular wrench

Over the past decade, significant progress has been made in synthesizing atomically precise carbon nanostructures, particularly graphene nanoribbons (NRs), employing advanced synthetic methodologies. Despite these advancements, achieving control over the stereochemistry of twisted NRs has proven to be a formidable challenge. This manuscript presents a strategic approach to achieve absolute control over the single-handed helical conformation in a cove-edged NR. This strategy leverages enantiopure helicenes as a molecular wrench, intricately influencing the overall conformation of the NR. [7]helicenes stitched to the terminal K-regions of a conjugated pyrene NR through a stereospecific annulative π-extension reaction to produce a helically twisted NR with an end-to-end twist of 171°. Furthermore, a detailed investigation of the impact of twisting on the conformational population was studied by quantum chemical calculations.

Benzodithiophene-Fused Cyclopentannulated Aromatics via a Palladium-Catalyzed Cyclopentannulation and Scholl Cyclodehydrogenation Strategy

We report the synthesis of a new class of cyclopenta-fused polyaromatic hydrocarbon (CP-PAH) incorporating fused benzodithiophene subunits. These CP-PAHs were prepared utilizing a two-step process involving a palladium catalyzed cyclopentannulation followed by a Scholl cyclodehydrogenation. This work broadens the scope of annulation chemistry by employing 1,2-bis(5-hexylthiophen-3-yl)ethyne and dibromoaryl derivatives based on anthracene, pyrene, and perylene to give 4,4',4'',4'''-(cyclopenta[hi]aceanthrylene-1,2,6,7-tetrayl)tetrakis(2-hexylthiophene), 4,4',4'',4'''-(dicyclopenta[cd,jk]pyrene-1,2,6,7-tetrayl)tetrakis(2-hexylthiophene), and 1,2,7,8-tetrakis(5-hexylthiophen-3-yl)-1,2,7,8-tetrahydrodicyclopenta[cd,lm]perylene. Scholl cyclodehydrogenation of the pendant thiophene units provided access to the π-extended polyaromatic systems 2,5,11,14-tetrahexylrubiceno[5,4-b:6,7-b':12,11-b'':13,14-b''']tetrathiophene, 2,5,11,14-tetrahexyldithieno-[4,5:6,7]indeno[1,2,3-cd]dithieno[4,5:6,7]indeno-[1,2,3-jk]pyrenes, and 2,9,12,19-tetrahexyldithieno[4,5:6,7]indaceno[1,2,3-cd]dithieno[4,5:6,7]indaceno[1,2,3-lm]perylene that possess helicene-like fragments. The anthracene-based CP-PAH was contorted owing to [5]helicene-like arrangements, while the pyrene- and perylene-based systems were essentially planar. The fully conjugated small molecules give low optical gaps (1.7-2.1 eV) with broad light absorption. The HOMO and LUMO energies of the CP-PAHs were found to be in the range of -5.48 to -5.05 eV and -3.48 to -3.14 eV, respectively. Finally, the anthracene-based CP-PAH was found to be a p-type semiconductor when tested in an organic field effect transistor.

Supertwistacene: A Helical Graphene Nanoribbon

This work describes a synthetic chiral graphene nanoribbon, named supertwistacene 1. It has four superbenzene (HBC) units linearly fused in a helical manner. The structure of 1, 4.3 nm in length, with an end-to-end twist of 117°, was confirmed by single-crystal X-ray diffraction. In contrast to various twistacene compounds and their analogues, 1 has a very stable configuration. It resists thermal isomerization even when being heated at 200 °C for 16 h. Enantiopure 1 obtained by chiral HPLC shows distinct CD signals in a broad spectral range until 600 nm. In addition, two smaller congeners of 1, the trimer 2 and the dimer 3, were also prepared and systematically investigated. Combining theoretical and experimental studies on 1-3 presents a big picture on their (chir)optical and electronic characteristics.

Nanographene and Graphene Nanoribbon Synthesis via Alkyne Benzannulations

The extension of π-conjugation of polycyclic aromatic hydrocarbons (PAHs) via alkyne benzannulation reactions has become an increasingly utilized tool over the past few years. This short review will highlight recent work of alkyne benzannulations in the context of large nanographene as well as graphene nanoribbon synthesis along with a brief discussion of the interesting physical properties these molecules display.

Construction of Polycyclic π-Conjugated Systems Incorporating an Azulene Unit Following the Oxidation of 1,8-Diphenyl-9,10-bis(phenylethynyl)phenanthrene

Polycyclic aromatic hydrocarbons (PAHs) that incorporate either heptagons or pentagons consist of non-planar molecular structures with unusual optoelectronic properties, and the design of a relatively simple and efficient method to construct these highly fused π-conjugated systems with odd-membered rings is in high demand. This work describes the use of silver(I) cations to promote the efficient synthesis of azulene-embedded PAH 2, which is a structural isomer of tribenzo[fg,ij,rst]pentaphene 3, via tandem oxidative transannulation between the phenyl and arylethynyl moieties. This method involves a carbophilic interaction of the silver(I) cation with the acetylene units, which facilitates an electron transfer in the initial step. The synthesized PAH 2 and the protonated cation 2 H⋅BF₄ were fully characterized by X-ray crystallographic analysis, electronic absorption, electrochemical measurement, and quantum chemical calculation. The azulene-embedded PAH 2 exhibited a low-energy absorption band and amphoteric redox events, which were characterized as non-alternant characteristics originating from the azulene unit.

Cyclopentannulation and cyclodehydrogenation of isomerically pure 5,11-dibromo-anthradithiophenes leading to contorted aromatics

Isomerically pure 5,11-dibromo-ADT was used to create contorted aromatics with large splay angles, low band gaps, and low LUMOs.

Conformational behavior and stacking interactions of contorted polycyclic aromatics

Computational studies of non-covalent dimers of saddle-shaped molecules unveil widely varying conformations and stacking configurations.