Research

We introduced the fold-in strategy for synthesizing curved aromatic molecules. A preorganized macrocyclic precursor undergoes a strain-generating transformation that folds its conjugated framework into a bowl, belt, or saddle.

Examples prepared in our laboratory include the molecular jellyfish chrysaorole, a triangular carbazole belt, and fluorene-containing chrysaorenes. Octulene, a hyperbolic analogue of kekulene, was also obtained through a fold-in transformation and unexpectedly binds chloride anions.

Curved aromatic molecules can be constructed by combining macrocyclic preorganization with reactions that generate strain or reorganize the molecular framework. We showed that nonclassical nanotube end-caps can be formed from strain-free precursors through synchronized homocoupling involving multinuclear metallacycles. We also used the masked-phenylene strategy, originally developed for circular nanohoops, to synthesize a radially conjugated molecular lemniscate.

A broader overview of synthetic approaches to curved aromatic molecules is available in our review article.

Expanding heterocyclic motifs in two dimensions creates heteroatom-doped nanographene analogues with potential applications as dyes and materials for organic electronics. Our group has developed several classes of such compounds, including peripherally expanded porphyrins and azacoronenes. These electron-rich systems can function as liquid crystals, multielectron donors, and aromaticity switches.

We developed donor–acceptor pyrrole building blocks for constructing diverse oligopyrrole chromophores, including porphyrins, snowflake-like and propeller-shaped azacoronenes, and bipyrrole boomerangs, some of which adopt persistent chiral configurations. These systems absorb strongly across the visible and near-infrared regions and can serve, for example, as dyes for antimicrobial photodynamic therapy. They can also accept multiple electrons, as many as ten in the case of azacoronenes, making them promising charge-storage materials.

Aromatic oligoradicals and oligoradicaloids have attracted sustained interest because of their unusual electronic structures and potential applications. Our studies of coronoids and nanographenes provide molecular platforms for such open-shell systems. We synthesized fully conjugated [4]chrysaorene, which splits iodine molecules while coupling redox switching with anion recognition. We also developed an efficient route to diindenophenanthrene, a stable derivative of Chichibabin's hydrocarbon. In related work on donor–acceptor nanographenes, we designed a 139-electron azacoronene radical that reversibly dimerizes to form a giant sandwich-like structure.