Morphological and Electronic Control of Interfacial Charge Transfer in 2D Transition Metal Dichalcogenide Hybrids

Interfacial charge-transfer (ICT) hybrids including transition metal dichalcogenides (TMDs) and phthalocyanines were synthesized and thoroughly characterized. The amount of noncovalently immobilized phthalocyanines per liquid-phase exfoliated (LPE) TMD flake increased exponentially with decreasing flake thickness. Steady-state spectroscopy revealed strong ground-state electronic coupling, evidenced by the emergence of distinct ICT bands. This allowed us to quantify ICT interactions in TMDs using a Mulliken-Hush approach. Also, strong excited-state electronic coupling led to significant quenching of phthalocyanine-centered fluorescence. Ultrafast transient absorption spectroscopy confirmed the formation of charge-separated states with lifetimes on the order of hundreds of picoseconds. These lifetimes remained largely unaffected by the number of TMD layers, underscoring the predominant role of surface-centered ICT interactions. Interestingly, depending on the relative alignment of electronic energy levels at the phthalocyanine/TMD interface, bidirectional charge transfer was also observed.