Spin State in Au Porphyrins Modulated by Charge Transfer on Au(111).

Controlling spin states at the single-molecule level is a crucial step toward functional molecular spintronic devices. Au porphyrins, as efficient electron acceptors, are highly sensitive to charge transfer on surfaces and offer a promising route to investigate spin-state modulation in single-molecule magnets. Here, we report the synthesis of phenalenyl-expanded Au porphyrins via cyclodehydrogenation on Au(111). The atomic-scale structures, electronic properties, and spin states of the products were investigated in detail with a combination of noncontact atomic force microscopy, scanning tunneling microscopy, scanning tunneling spectroscopy, as well as density functional theory and multireference quantum chemistry calculations. Although the structures are nearly identical, the spin states of the porphyrins are significantly affected by the charge state of the Au complex. Our findings show that the role of the molecule-substrate interactions and the resulting charge transfer of the gold complex tune the spin and electronic properties of the extended porphyrins, establishing them as versatile molecular platforms for investigating charge-transfer-driven spin switches and guiding the design of molecular spintronic devices.