Controlled assembly of two-dimensional porphyrin heterostructures toward directed energy transfer and charge separation.

The exceptional efficiency of natural light-harvesting systems arises from their precisely organized supramolecular architectures. Reproducing such structural control in synthetic aqueous assemblies, particularly over size and dimensionality, remains a formidable challenge. Here, we report a general seeded-growth strategy that enables precise, hierarchical assembly of two-dimensional (2D) porphyrin heterostructures in water. Integrating π-π stacking, hydrogen bonding, and hydrophobic interactions, the porphyrin amphiphiles follow a metastable assembly pathway that yields kinetically controlled nanosheets or heterostructures. This approach provides unprecedented control over the nanostructure area across two orders of magnitude, establishing a versatile platform for complex functional architectures. By integrating a cobalt-porphyrin acceptor via block co-assembly, we construct 2D donor-acceptor heterostructures that achieve a directed energy funneling. Ultrafast spectroscopic analysis combined with global fitting reveals the mechanism: the controlled 2D heterostructures promote exciton migration at rates 2.5-fold greater than in homostructures and drive the formation of a fully charge-separated state on a sub-nanosecond timescale, with dynamics that scale with platelet dimensions. This work establishes a synthetic route to biomimetic 2D heterostructures and elucidates the structural determinants of directed exciton and charge flow, offering key design principles for advanced biomimetic systems.