Observing π-Au Interaction between Aromatic Molecules and Single Au Nanodimers with a Subnanometer Gap by SERS.

Interface interaction between aromatic molecules and noble metals plays a prominent role in fundamental science and technological applications. However, probing π-metal interactions under ambient conditions remains challenging, as it requires characterization techniques to have high sensitivity and molecular specificity without any restrictions on the sample. Herein, the interactions between polycyclic aromatic hydrocarbon (PAH) molecules and Au nanodimers with a subnanometer gap are investigated by surface-enhanced Raman spectroscopy (SERS). A cleaner and stronger plasmonic field of subnanometer gap Au nanodimer structures was constructed through solvent extraction. High sensitivity and strong π-Au interaction between PAHs and Au nanodimers are observed. Additionally, the density functional theory calculation confirmed the interactions of PAHs physically absorbed on the Au surface; the binding energy and differential charge further theoretically indicated the correlation between the sensitivity and the number of PAH rings, which is consistent with SERS experimental results. This work provides a new method to understand the interactions between aromatic molecules and noble metal surfaces in an ambient environment, also paving the way for designing the interfaces in the fields of catalysis, sensors, and molecular electronics.