Soluble Graphene Nanoarchitectures
Authors: Bunz Uwe , Narita Akimitsu , Ikai Tomoyuki , Chi Chunyan 
Published: October 2024

In this Cheminar, we will delve into the latest research advancements in the organic synthesis, characterization, and application of soluble graphene nanoarchitectures. The discussion will encompass a diverse range of structures and innovative functionalizations that are pushing the boundaries of this dynamic field.

The event will be chaired by Prof. Akimitsu Narita from the Okinawa Institute of Science and Technology Graduate University, Japan.

Featured Speakers:

• Prof. Chunyan Chi (National University of Singapore, Singapore)

• Prof. Uwe Bunz (Ruprecht-Karls-University Heidelberg, Germany)

• Prof. Tomoyuki Ikai (Nagoya University, Japan)

Stabilization of Acenes and Azaacenes

In the past we have developed new synthetic apporaches to azapentacenes and azahexacenes, stabilized by TIPS-ethynyl groups. Now our focus has shifted into stabilizing very large (heptacene and beyond) acenes and azaacenes. This can be done for azaheptacenes and nonacenes by introducing four to six TIPS-ethynl groups on every other ring and reasonably stable species were isolated. To go beyond the nonacene limit, alternative methods of stabilization are needed. We converted pentacene-5,7,12,14-tetraone in two steps into a doubly bridged (2,2”'-substituted 1,1':4',1”:4”,1”'-quaterphenyl) pentacene, which is ca. 65 times more stable than TIPS-pen.

Control of Secondary Structure in Designed Ladder Polymers

Recent advancements in synthetic methodologies have greatly expanded the range of molecules and polymers accessible for chemists, increasing the potential for significant breakthroughs in materials science. Polymers with a molecular-level ladder structure, in which cyclic repeating units are interconnected by two or more chemical bonds, are referred to as ladder polymers.1 Due to their rigid backbone structures, ladder polymers display superior mechanical properties and thermal stability compared to conventional linear polymers linked by single chemical bonds. The severely restricted conformational freedom is also a defining characteristic of ladder polymers, offering a high degree of structural designability that allows precise control of the secondary structure in synthetic polymers. However, the synthesis of well-defined ladder polymers without branching or imperfect ladder formation remains a significant challenge for organic and polymer chemists.
We have previously developed an efficient approach to ladder formation2 by modifying the acid-promoted alkyne benzannulations developed by Swager et al.3,4 This has led to the successful synthesis of ladder polymers with well-defined helical2,4–7 and coplanar2 geometries, free from detectable levels of structural defects, based on the appropriate design of chiral and achiral monomeric units. Recently, we designed and synthesized a series of helical ladders by incorporating pi-extended achiral spacer units as a third comonomer component, alongside the chiral and achiral units.8 This design allowed the modulation of the secondary structures with different helical handedness (P or M) and geometry (extended ribbon-like or loose coil helix) by replacing the achiral spacer units in the main chain while retaining the chiral monomer units. This talk will detail the design and synthesis of such chiral ladder architectures, highlighting their chiral functions, particularly with respect to circularly polarized luminescence and chiral recognition.

Molecular Carbons with Different Shapes and Sizes

Carbon-based nanostructures have shown revolutionary influence in the area of chemistry, physics and materials science. Recent efforts have been focused on novel topological structures of sp2-carbons such as carbon nanohoops, nanobelts, molecular cages, and open-shell nanographenes, which provoked new chemistry and materials. However, synthesis of this kind of molecules is extremely challenging mainly due to strain or intrinsic high reactivity. Another issue is that most of these carbon nanostructures have a localized aromatic character; that means, the π-electrons are not globally delocalized along the backbone, which limits their optical and electronic properties and applications. Herein, the synthesis of a series of novel pi-structure with different shapes will be introduced, and their physical properties, aromaticity and diradical character will be discussed.