Research

We have introduced the fold-in strategy for synthesizing curved aromatic molecules. In this method, a macrocyclic precursor is subjected to a strain-inducing reaction to produce a distorted conjugated structure. The fold-in method is particularly well suited for the synthesis of bowl-shaped, belt-shaped, and saddle-shaped molecules, but it can also be used to prepare planar coronoid macrocycles.

Examples of molecules synthesized in our laboratory using the fold-in method include the molecular jellyfish, named chrysaorole, a triangular carbazole belt, and fluorene-containing chrysaorenes. Octulene, the hyperbolic analogue of kekulene, was also obtained in a fold-in reaction and showed a surprising ability to bind chloride anions.

We also explore alternative approaches to highly strained aromatic systems. In particular, we showed that highly strained non-classical nanotube end-caps can be obtained from strain-free precursors by "synchronized homocoupling," a process involving multinuclear metallacycles. More recently, we used the masked phenylene strategy, originally developed for the synthesis of circular nanohoops, to synthesize a molecular lemniscate characterized by radial conjugation.

A general discussion of synthetic methods used to construct curved aromatic molecules can be found in our review.

Expansion of heterocyclic motifs in two dimensions creates heteroatom-doped analogues of nanographenes, which are of interest as dyes and materials for organic electronics. Our group has developed several types of such compounds, including peripherally expanded porphyrins and azacoronenes. These electron-rich systems can function as liquid crystals, multi-electron donors, and aromaticity switches.

We reported the synthesis of donor-acceptor pyrrole building blocks that can be used to construct a variety of oligopyrrole chromophores, including porphyrins, snowflake-like or propeller-shaped azacoronenes, and bipyrrole boomerangs, some of which adopt persistent chiral configurations. These donor-acceptor systems absorb strongly in the visible and near-infrared ranges and can be used, for example, as dyes for antimicrobial photodynamic therapy. Another notable feature is the ability of these molecules to accept multiple electrons, up to ten in azacoronenes, which makes them of interest as charge-storage materials.

Aromatic oligoradicals and oligoradicaloids have been intensely investigated for more than a century because of their exceptional electronic structures and potential applications. Our research on coronoids and nanographenes provides opportunities to create oligoradical frameworks. As part of these investigations, we reported the synthesis of fully conjugated [4]chrysaorene, which can split iodine molecules, combining redox switching with anion-receptor chemistry. In parallel work, we established an effective strategy to obtain diindenophenanthrene, a stable derivative of Chichibabin's hydrocarbon. In our work on donor-acceptor nanographenes, we designed a 139-electron azacoronene radical that reversibly recombines into a giant sandwich-like dimer.