Regioisomerism Rewires Optical and Ion Recognition Properties in Azulenylsumanenes-Curved Non-Alternant π-Systems

Herein, we explore the fundamental concept of combining the molecular curvature of a molecular fragment of buckminsterfullerene with the pronounced spatial separation of HOMO and LUMO orbitals of a non-alternant polycyclic aromatic hydrocarbon (PAH) within a single molecule. To this end, we report the first synthesis of azulene-sumanene hybrids (6 and 7), two isomeric, bowl-shaped PAHs. Integration of azulene and sumanene motifs into a single molecular framework yields dual-responsive systems exhibiting unprecedented regioisomer-dependent electronic properties. Distinct orientations of the polarized azulene moiety relative to the curved sumanene core confer divergent receptor properties in 6 and 7, as reflected in their distinct proton-induced colorimetric responses and fluorescence enhancement upon binding alkali metal cations. These regioisomeric conjugates display markedly different selectivity toward alkali metal cations in aqueous media, with preferentially binding rubidium ions or selective detection of sodium ions, both with low detection limits at the µM level, demonstrating the electronic control of ion recognition in curved non-alternant π-systems. By tuning the electronic polarity of curved π-surfaces, this represents a significant advance in the chemistry of sumanene receptors, typically selective for cesium ions. We believe this work will stimulate future advances in the basic and applied sciences of π-conjugated and bowl-shaped nanographenes.