Unveiling the Role of the Central Metal in Electron Delocalization Dynamics at Phthalocyanine/ReS2 Interfaces Probed by Resonant Photoemission Spectroscopy

Abstract

Engineering interfacial charge-transfer processes is crucial for developing metal-phthalocyanine/2D semiconductor heterostructures, where molecular orbital hybridization can be tuned by the central metal ion. Herein, we investigate the influence of the central cation at phthalocyanine/ReS2 interfaces by comparing metal-free H2Pc and CuPc films using resonant photoemission spectroscopy (RPES), supported by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS). Compared with H2Pc/ReS2, XPS reveals distinct molecule–substrate interactions in CuPc/ReS2, including systematic shifts of the C 1s components toward higher binding energy and a reduced C–N/C–C intensity ratio, indicating modified interfacial charge redistribution. N K-edge NEXAFS shows that the presence of the central Cu ion alters the unoccupied electronic structure, introducing metal–ligand hybridization and a singly occupied molecular orbital (SOMO)-related feature that is absent in H2Pc. Polarization-dependent spectra indicate that both molecules adopt a preferential edge-on configuration on ReS2, with an average tilt angle of ∼46°. RPES directly probes electron delocalization dynamics across the interface. For H2Pc/ReS2, ultrafast charge transfer from the LUMO to the ReS2 conduction band occurs within the N 1s core-hole lifetime, with characteristic times of 4.39 ± 0.05 fs (Naza 1s → LUMO) and 6.24 ± 0.10 fs (Npyr 1s → LUMO). In contrast, no interfacial charge transfer is observed for CuPc/ReS2 within either the N 1s or Cu L3 core-hole lifetimes. Density functional theory calculations support these findings, showing that strong N–Cu hybridization in CuPc localizes the frontier orbitals and suppresses charge transfer across the interface. These findings establish central-metal engineering as an effective strategy to control interfacial charge-transfer pathways in hybrid organic/2D semiconductor heterostructures for electronic and optoelectronic applications.