Diblock Copolypeptide Amphiphiles-Mediated Assembly and Structural Modulation of Porphyrin Dimers in Aqueous Media

We report the design and self-assembly of supramolecular nanohybrids composed of a lipophilic zinc porphyrin dimer (ZnP)₂ and diblock copolypeptide amphiphiles. The peptide amphiphiles were designed with hydrophilic segments containing aspartic acid (Asp) and lysine (Lys) residues that favor β-sheet formation and hydrophobic segments composed of leucine (Leu) residues that drive aggregation in aqueous media. This balance of hydrophobic and hydrophilic interactions promotes the spontaneous formation of nanostructures such as vesicles and lamellae in aqueous media, resulting in highly organized hybrid assemblies. UV-vis absorption and fluorescence spectroscopy revealed that the interaction between (ZnP)₂ and the peptides significantly affects the conformation of the porphyrin units. Absorption spectra showed shifts in the B (Soret) and Q bands upon hybridization, reflecting changes in π-conjugation and planarity. Fluorescence emission spectra, particularly those excited at the B band (443 or 494 nm), displayed a distinct band around 741 nm, attributed to the planar conformation of (ZnP)₂. The corresponding excitation spectra matched well with the absorption features of planar (ZnP)₂, confirming the selective excitation of these conformers. Spectroscopic analyses, including IR and circular dichroism spectroscopy, reveal that the polypeptide components adopt β-sheet-rich secondary structures, which play a critical role in inducing and stabilizing the planar conformation of the embedded (ZnP)₂ units. Importantly, the planar conformation of (ZnP)₂ is induced by strong intramolecular exciton coupling between the porphyrin chromophores, as evidenced by distinct luminescence spectra in the near IR region. Moreover, the incorporation of Asp residues into the hydrophilic domain further promotes β-sheet formation, contributing to the structural integrity and water solubility of the nanohybrids, leading to intermolecular interactions between (ZnP)₂s in copolypeptide amphiphiles. These results demonstrate that cooperative self-assembly of metal complexes with sequence-defined polypeptide amphiphiles enables the emergence of dynamically responsive and functional supramolecular materials in water, offering new design principles for optoelectronic and bioinspired nanomaterials.