A quadruple helicene with a rubicene core: synthesis, structural analyses and properties

Heptagon-Embedded Helicene Derivatives: Synthesis, Crystal Structural Analyses, and Circularly Polarized Luminescence

Two pairs of isomers of heptagon-embedded helical arenes (3/6 and 10/13) have been strategically prepared, where the molecular structures of 3 and 13 have been identified through single crystal X-ray diffraction analysis. The effect of the heptagon unit on the physical properties of 3, 6, 10, and 13 is investigated in a comparative manner, and the results indicate that the optical enantiomers of 13 obtained from HPLC exhibit promising chiroptical properties.

Synthesis and Properties of Rubicene-Based Aromatic π-Conjugated Compounds as Five-Membered Ring Embedded Planar Nanographenes

Polycyclic aromatic hydrocarbons consisting of two or three rubicene substructures were designed as π-conjugated compounds embedding five-membered rings. The target compounds with t-butyl groups were synthesized by the Scholl reaction of precursors consisting of 9,10-diphenylanthracene units, even though a partially precyclized precursor was required for the synthesis of the trimer. These compounds were isolated as stable and dark blue solids. Single-crystal X-ray analysis and DFT calculations revealed the planar aromatic framework of these compounds. In the electronic spectra, the absorption and emission bands were considerably red-shifted compared with those of the reference rubicene compound. In particular, the emission band of the trimer extended to the near-IR region while retaining the emissive property. The narrowed HOMO-LUMO gap with the extension of the π-conjugation was confirmed by cyclic voltammetry and DFT calculations.

Synthesis of Highly Luminescent Chiral Nanographene

Chiral nanographenes with both high fluorescence quantum yields (Φ_F ) and large dissymmetry factors (g_lum ) are essential to the development of circularly polarized luminescence (CPL) materials. However, most studies have been focused on the improvement of g_lum , whereas how to design highly emissive chiral nanographenes is still unclear. In this work, we propose a new design strategy to achieve chiral nanographenes with high Φ_F by helical π-extension of strongly luminescent chromophores while maintaining the frontier molecular orbital (FMO) distribution pattern. Chiral nanographene with perylene as the core and two dibenzo[6]helicene fragments as the wings has been synthesized, which exhibits a record high Φ_F of 93 % among the reported chiral nanographenes and excellent CPL brightness (B_CPL ) of 32 M^-1  cm^-1 .

The Scholl Reaction as a Powerful Tool for Synthesis of Curved Polycyclic Aromatics

The past decade has witnessed remarkable success in the synthesis of curved polycyclic aromatics through Scholl reactions which enable oxidative aryl-aryl coupling even in company with the introduction of significant steric strain. These curved polycyclic aromatics are not only unique objects of structural organic chemistry in relation to the nature of aromaticity but also play an important role in bottom-up approaches to precise synthesis of nanocarbons of unique topology. Moreover, they have received considerable attention in the fields of supramolecular chemistry and organic functional materials because of their interesting properties and promising applications. Despite the great success of Scholl reactions in synthesis of curved polycyclic aromatics, the outcome of a newly designed substrate in the Scholl reaction still cannot be predicted in a generic and precise manner largely due to limited understanding on the reaction mechanism and possible rearrangement processes. This review provides an overview of Scholl reactions with a focus on their applications in synthesis of curved polycyclic aromatics with interesting structures and properties and aims to shed light on the key factors that affect Scholl reactions in synthesizing sterically strained polycyclic aromatics.

Corannulene-based acenes

Synthesis of diacenes still represents a considerable challenge due to their poor stability and low solubility.

Thiophene/selenophene-based windmill-shaped triple [6]helicenes

The construction of four windmill-shaped triple [6]helicenes with the substitution from S to Se in the molecular skeletons are studied. The properties of their crystal structures, spectroscopic behaviors and chirality are investigated.

A Distorted Hybrid Corannulene-Dibenzobistetracene

We have designed and synthesized a new type of distorted nanographene by Diels-Alder and Scholl reactions that contains one dibenzobistetracene (DBT, 1) core and two end-capping corannulene units. Single-crystal X-ray diffraction analyses demonstrate that nanographene 1 contains two [5] helicene subunits with a dihedral angle of 62°, consequently leading to the distorted DBT core. In addition, the photophysical properties and (non)aromaticity of 1 were investigated by the absorption and emission spectra in combination with theoretical calculations.

Double π-Extended Helicene Derivatives Containing Pentagonal Rings: Synthesis, Crystal Analyses, and Photophysics

Two novel double π-extended [n]helicene (n = 5, 6) derivatives (7b and 9) including pentagonal rings have been synthesized and characterized. Both of them have three isomers containing two enantiomers (P₆), (M₆), and a diastereoisomer in a meso form (P,M). X-ray single crystal analyses suggest that molecules 7b and 9 exhibit offset packing models of (P₆,P₅)- and (M₆,M₅)-isomers. Optical resolution of the resultant compound 7b was finished, and their chiroptical properties, as well as the DFT calculations, were also examined.

Corannulene-based nanographene containing helical motifs

The synthesis and structural analyses of corannulene-PAH hybrids 1 with a [4] helicene subunit and 2 with a [7] helicene subunit have been reported.