Substrate-driven modulation of interfacial charge transfer dynamics in cobalt phthalocyanine–2D material van der Waals heterostructures

The substrate-driven modulation of interfacial charge transfer in redox-active cobalt phthalocyanine (CoPc)-two-dimensional (2D) material heterostructures was investigated using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and resonant photoemission spectroscopy (RPES). Graphene (Gr), tungsten disulfide (WS₂), and rhenium disulfide (ReS₂) were selected as representative 2D substrates with distinct electronic structures and morphologies. Raman mapping confirmed the formation of vertically stacked CoPc-2D architectures. The broadening of the 2D-layer Raman modes evidences interfacial charge transfer that enhances electron-phonon scattering, most pronounced in CoPc-Gr, consistent with stronger molecule-substrate coupling. XPS analysis highlights the key role of Co-N(pyrrole) species in mediating electronic interactions. Polarization-dependent N K-edge NEXAFS reveals a preferential edge-on molecular orientation, attributed to the surface roughness of the 2D materials. Charge-transfer dynamics, quantified using the core-hole clock method, were investigated for CoPc on Gr, WS₂, and ReS₂, showing clear substrate dependence. Charge transfer during the N 1s core-hole lifetime occurs for electrons excited into both LUMO and LUMO+1 states, with the fastest transfer observed for CoPc-Gr (<i>τ</i>_CT ≈ 14 and 9 fs), due to the strong coupling between CoPc LUMOs and graphene π states. A similar but weaker interaction with WS₂ d states also promotes efficient transfer, whereas in CoPc-ReS₂, the reduced orbital overlap arising from the in-plane anisotropy of ReS₂ leads to longer <i>τ</i>_CT values. These findings provide mechanistic insight into substrate-governed charge-transfer processes in organic-2D hybrid systems, offering valuable guidance for the design of next-generation optoelectronic devices.