Iron tetraphenylporphyrin chloride–metal substrate interaction mediated by a graphene buffer layer

We investigate the interfacial electronic structure of monolayer iron tetraphenylporphyrin chloride (FeTPP-Cl) adsorbed on graphene (Gr) buffer layers supported by Ni(111) and Pt(111). This study unveils the role of a graphene buffer layer in controlling the charge transfer mechanisms of self-assembled porphyrins on metal surfaces, reshaping interfacial energy level alignment, charge transfer dynamics, interface dipoles, and charge injection barriers. By exploiting the intrinsic n- and p-type doping of graphene on Ni and Pt, we modulate the charge transfer behavior in iron tetraphenylporphyrin monolayers, using these systems as model platforms to probe interfacial electronic processes and the impact of graphene-substrate coupling. Through a comprehensive multi-technique approach, combining X-ray photoemission, ultraviolet photoemission, and X-ray absorption spectroscopies, we demonstrate how substrate-induced doping drives significant changes at the molecule-graphene-metal interface. Core-level binding energies (BEs) and ionization potentials (IPs) indicate weak physisorption in both systems, with opposite charge transfer directions depending on the substrate, despite similar molecular morphologies. ... mehrOn Gr/Ni(111), all core levels shift to higher BE, with a pronounced +0.6 eV shift in Fe 2p and a +0.15 eV IP increase, indicating electron transfer from the substrate to the molecule localized at the Fe center. On Gr/Pt(111), C 1s and N 1s shift to lower BE and the IP decreases by -0.15 eV, consistent with electron donation from the molecule to the substrate, more delocalized on the macrocycle. The small interface dipoles (-0.15 eV for Ni, -0.25 eV for Pt) and the absence of rigid shifts demonstrate that charge redistribution is fractional and site-specific, governed primarily by electrostatics and graphene doping rather than strong hybridization. These findings suggest that the interaction strength and electronic behavior at the interface are governed by the underlying metal, with Gr acting as an effective electronic decoupler or mediator. Our study highlights the importance of the graphene-metal interface in modulating charge transfer and level alignment in porphyrin-based hybrid systems.