Revealing unconventional host-guest complexation at nanostructured interface by surface-enhanced Raman spectroscopy

Interfacial host-guest complexation offers a versatile way to functionalize nanomaterials. However, the complicated interfacial environment and trace amounts of components present at the interface make the study of interfacial complexation very difficult. Herein, taking the advantages of near-single-molecule level sensitivity and molecular fingerprint of surface-enhanced Raman spectroscopy (SERS), we reveal that a cooperative effect between cucurbit[7]uril (CB[7]) and methyl viologen (MV(2+)2I(-)) in aggregating Au NPs originates from the cooperative adsorption of halide counter anions I-, MV2+, and CB[7] on Au NPs surface. Moreover, similar SERS peak shifts in the control experiments using CB[n]s but with smaller cavity sizes suggested the occurrence of the same guest complexations among CB[5], CB[6], and CB[7] with MV2+. Hence, an unconventional exclusive complexation model is proposed between CB[7] and MV2+ on the surface of Au NPs, distinct from the well-known 1:1 inclusion complexation model in aqueous solutions. In summary, new insights into the fundamental understanding of host-guest interactions at nanostructured interfaces were obtained by SERS, which might be useful for applications related to host-guest chemistry in engineered nanomaterials.

Automated summary

Interfacial host-guest complexation is a versatile way to functionalize nanomaterials, but the study of it is difficult due to the complicated interfacial environment. Using surface-enhanced Raman spectroscopy (SERS), a cooperative effect between CB[7] and MV2+ on aggregating Au NPs was revealed, along with similar guest complexations among CB[n]s and MV2+. This unconventional exclusive complexation model provides new insights into host-guest interactions at nanostructured interfaces, which could be beneficial for applications in engineered nanomaterials.