Butadiyne-Bridged (Porphinato)Zinc(II) Chromophores Assemble into Free-Standing Nanosheets

The molecular engineering of chromophores that enables the controlled and reliable formation of hierarchical solid-state architectures is at the forefront of developing hybrid semiconducting materials. While the rules and principles to assemble monomeric porphyrin-derived building blocks are well established, the aggregation of larger π-conjugated cores that feature electronically coupled porphyrin arrays has been vastly underexplored. In the present contribution, we report the synthesis, spectroscopy, assembly, and solid-state properties of a class of butadiyne-bridged (porphinato)­zinc­(II) dimer chromophores. A spectroscopic investigation unraveled the formation of aggregates in an aqueous medium, leading to the formation of two-dimensional objects that expanded across microscale dimensions. An analysis of the height profile, by atomic force microscopy, indicated that one porphyrin dimer comprises the thickness of the solid-state hierarchical superstructure, which underscores the promise of this approach to engineer solid-state platforms for (opto)­electronic devices. Furthermore, the initiation of noncovalent interactions between building blocks by means of a chemical stimulus (pH) revealed that a nucleation–growth process governs the aggregation of the π-conjugated chromophores in an aqueous medium. This work provides tools to modulate the structure–function relationships of supramolecular architectures equipped with enticing optical properties.