Controlling the Flow of Charges across Phthalocyanine@Transition-Metal Dichalcogenide Interfaces

We describe herein the preparation of exfoliated transition-metal dichalcogenides (TMDs) and their heterostructures with phthalocyanines complemented by their in-depth (photo)physical investigation. We focused on six different zinc phthalocyanines (ZnPcs) as light harvesters and electron donors/acceptors. All of them were shown to interact strongly with the exposed surface of TMDs in dispersion (s-TMD) as well as thin film nanosheet networks (NN-(s-TMD)). The corresponding heterostructures, that is, ZnPc@NN-(s-MoS₂) and ZnPc@NN-(s-WS₂), were characterized by steady-state and pump-probe femtosecond transient absorption spectroscopy, as well as Raman and X-ray photoelectron spectroscopies (XPS) to shed light onto electron donor-acceptor interactions. Supported by density functional theory calculations and molecular dynamics simulations, we identified newly evolving charge-transfer absorptions in the electronic ground-state and confirmed the separation of charges in the electronic excited-state. Importantly, the direction in which charges flow in the electronic excited state depends on the relative positioning of the TMD bands and the molecular orbitals of the different ZnPcs. Key to control is tailoring the energetic position of the ZnPc HOMOs and LUMOs relative to the TMD bands.