Tuning the Optoelectronic Properties of Vanadyl Phthalocyanine through Molecular Orientation on van der Waals Material Substrates

Vanadyl phthalocyanine (VOPc) is an organic molecule that has attracted attention for potential as a spin qubit and as an active material in optoelectronic devices due to its favorable charge transport properties and broad-spectrum light absorption. Numerous studies have characterized the magnetic properties of the vanadium as well as the optical properties of the phthalocyanine ring in single-molecule VOPc, yet the versatile optical properties of VOPc thin films remain underexplored. In this work, we demonstrate how the optical emission from VOPc thin films can be tuned via the orientation of the molecules on a substrate. Specifically, we show that when VOPc films less than 1 nm thick are deposited on a van der Waals material, the molecules adopt a highly ordered bilayer configuration. This configuration suppresses native emission from the phthalocyanine ring and introduces a novel photoluminescence feature that arises from interactions between the phthalocyanine ring and vanadium. Our work demonstrates that molecular orientation can be used as a tool to control the optoelectronic properties of VOPc for device applications and demonstrates the potential to impart properties of the center transition metal onto optical emission.