Abstract
Two-dimensional material-enhanced Raman spectroscopy (2DERS) is an extension of surface-enhanced Raman spectroscopy that leverages the unique properties of 2D materials’ atomically flat, dangling-bond-free interfaces and absence of electromagnetic hot spots—to provide reproducible Raman enhancement of analyte molecules. Although mechanisms like charge transfer and structural matching have been explored, the influence of analyte orientation and its configuration with 2D materials remains underexplored. To address this gap, we study interactions between 2D materials (graphene and MoS2) and planar/non-planar dye molecules in two configurations: atop and beneath the 2D material. For dyes atop graphene, we observe enhanced Raman signals for stretching modes and significant fluorescence quenching, indicating stronger adsorption than in the dye-beneath case. Additionally, non-planar dyes exhibit unusual enhancement in phenyl ring vibrational modes, suggesting partial flattening to better conform to the graphene surface—a behavior not observed for planar dyes or those on MoS2. First-principles calculations reveal distinct charge transfer characteristics and stable adsorption geometries that support these observations. Our findings highlight the critical role of molecular geometry and configuration in 2DERS and bridge experimental insights with theoretical understanding. This work advances 2DERS mechanisms and paves the way for developing precise, graphene-based chemical sensing platforms.
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•Molecular Configuration Matters: Raman enhancement depends strongly on dye position (atop vs. beneath) and structure (planar vs. non-planar), with non-planar dyes atop graphene showing the strongest signals.•Phenyl Ring Reorientation: Non-planar dyes show unique Raman mode shifts due to changes in phenyl ring angles when directly adsorbed on graphene.•Substrate-Dependent Interaction: Graphene enables stronger charge transfer and adsorption than MoS2, leading to higher Raman enhancement and fluorescence quenching.•Theory Supports Findings: DFT calculations confirm greater electron transfer and partial phenyl ring flattening on graphene, matching experimental trends.