Interfacial Behavior, Supramolecular Assembly, and Photophysics of Phospholipid–Porphyrin and Phospholipid–Phthalocyanine Conjugates

The design of supramolecular assemblies based on phospholipid-porphyrinoid conjugates has attracted growing attention in recent years, particularly for biomedical applications. Here, we report two novel amphiphilic conjugates, ZnPor(PL)₄ and ZnPc(PL)₄, obtained by coupling four molecules of 1-myristoyl-2-(14-carboxymyristoyl)-sn-glycero-3-phosphocholine to zinc(II)-tetraaminophenylporphyrin or zinc(II)-tetraaminophthalocyanine, respectively. Their interfacial behavior, their supramolecular assemblies in aqueous media, and photophysical properties were systematically investigated. Monolayer studies at the air/buffer interface revealed distinct molecular orientations. ZnPor(PL)₄ formed a compact and ordered monolayer with the porphyrin core pushed upward between lipid chains, whereas ZnPc(PL)₄ exhibited expanded and less ordered monolayer due to the higher rigidity and planarity of the phthalocyanine macrocycle. In solution, ZnPor(PL)₄ self-assembled into chiral nanofibers stabilized by π-π stacking and hydrogen bonding, whereas ZnPc(PL)₄ generated planar bilayer-like membrane patches. Both assembled conjugates exhibited strong fluorescence quenching; notably, ZnPor(PL)₄ displayed pronounced tetrasignate circular dichroism signals consistent with right-handed helical H-aggregates. Molecular dynamics simulations corroborated these findings and demonstrated that hydrogen bonding and intrinsic chirality of phospholipid headgroups govern the supramolecular helicity. Overall, this work highlights how chromophore structure controls interfacial orientation and self-assembly in lipid-porphyrinoid conjugates, offering design principles for light-responsive nanostructures with potential applications in photodynamic and photothermal therapies.