Interfacial forces driving conformation and charge transfer in protoporphyrin IX–graphene based nanohybrids

Nanohybrids of porphyrins and graphene-based materials (Por-GBMs), in which the interfacial structure controls function, are promising platforms for optoelectronics, energy conversion, and photomedicine. Here, we investigate the non-covalent adsorption and photophysics of solid-state protoporphyrin IX (PPIX) ultrathin layers on graphene oxide (GO) and reduced graphene oxide (RGO). Co-localized atomic force microscopy, photoluminescence (PL) mapping, and light-assisted Kelvin probe force microscopy (KPFM), supported by molecular dynamics simulations, reveal that on GO, PPIX anchors via the electrostatic interactions of its propionic side chains with GO oxygenated groups, inducing macrocycle distortions and changes in the PPIX emission spectrum with partial intensity quenching. On RGO, π–π stacking stabilizes planar dense PPIX assemblies that enable efficient photoinduced electron transfer, producing strong PL suppression and a pronounced surface photovoltage. These results establish how nanoscale assembly governs conformation and charge transfer, providing a framework for rationally engineering Por-GBMs for light harvesting, optoelectronics, and photodynamic therapy. • Interfacial forces dictate PPIX assembly on GO versus RGO. • GO induces macrocycle distortions, reshaping porphyrin emission spectra. • RGO stabilizes planar PPIX assemblies enabling efficient charge transfer. • Structure–function correlation guides design of porphyrin–graphene hybrids.