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

Abstract

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 (MV2+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.

Fermi Level Equilibration at the Metal–Molecule Interface in Plasmonic Systems

“…However, when the metal surface is occupied with molecules with a stronger affinity for the metal surface than halide ions, such as thiolated molecules, the halide ions cannot coadsorb on the surface, which can be readily checked experimentally through the Ag-halide SERS bands (also valid for Au NPs). − Thus, in these systems halides’ catalytic role involves scavenging the hot holes created through SPR excitations or inter- and intraband transitions. , These results highlight the important and many-times underestimated role of capping agents, electric double layer, reaction media, and halides coadsorption in plasmonic catalysis and surface-enhanced spectroscopies.…”

Simple Approach to Assess the Maximum Hot Spot SERS Enhancement Factors in Colloidal Dispersions of Gold Nanoparticle Aggregates

“…The most intense Raman mode located at 630 cm –1 in the SERS spectrum corresponds to the C–S stretching vibration of cysteamine . The conventional Raman spectrum of MV (panel B, blue curve) presents two Raman modes at 1300 and 1653 cm –1 , corresponding to ring breathing/C–C stretching and CC stretching/CH 3 bending, respectively . Both Raman modes are also present in the SERS spectrum at 1284 and 1636 cm –1 .…”

“…39 The conventional Raman spectrum of MV (panel B, blue curve) presents two Raman modes at 1300 and 1653 cm −1 , corresponding to ring breathing/C−C stretching and CC stretching/CH 3 bending, respectively. 40 Both Raman modes are also present in the SERS spectrum at 1284 and 1636 cm −1 . The difference broadening for these modes in the conventional Raman and SERS spectra could be due to an inhomogeneous broadening given by the intermolecular interaction between CB [6] and MV in the SERS spectrum that produces a small perturbation in the electronic structure of MV (enhanced by the SERS effect).…”

A Modified Oxazolone Dye Dedicated to Spectroscopy and Optoelectronics

“…Indeed, there are research fields, like photonics, , optoelectronics, spectroscopy, , medicine, and industrial areas, such as complex networks, optical databases, , and logic and/or optical gates, where remote-controlled materials, especially those driven by light, are the most appealing ones. According to the reasons listed above, there are already few different approaches for designing such working organic systems, starting from organic low-molecular units embedded into branched and complex matrices , and passing by nano-object utilization in both organic/inorganic systems up to the macromolecular, self-organizing, and functional systems . Understandably, each of them has advantages but also has drawbacks.…”