Spin-orbit coupling (SOC) lifts molecular orbital degeneracy, enabling bilevel electronic platforms suitable for next-generation digital devices. However, common light-atom molecular feedstocks exhibit weak SOC due to the absence of heavy elements. To enhance SOC without synthesizing new materials, we leverage interfacial interactions between molecules and transition-element-based solid-state materials. This computational study investigates SOC splitting in metal-phthalocyanine adsorbed on transition metal dichalcogenides (TMDs) using density functional theory (DFT). The enhanced SOC splitting is attributed to strong orbital hybridization at the molecule-substrate interface. Specifically, Zn-phthalocyanine (ZnPC) on monolayer $\mathrm{Mo}{\mathrm{S}}_2$ achieves a notable SOC splitting of $\sim 8$ meV. Furthermore, when ZnPC forms self-assembled chains on $\mathrm{Mo}{\mathrm{S}}_2$, the splitting increases to $\sim 20$ meV, driven by the formation of hybrid bands modulated by molecular periodicity. These findings highlight the role of interfacial and intermolecular interactions in inducing and enhancing SOC in surface-adsorbed molecules, providing a new strategy for molecular spintronic materials without complex synthetic efforts.

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• Density functional theory
• Spin-orbit coupling
• Spintronics
• Surface & interfacial phenomena
• 2-dimensional systems
• Molecules