Surface Ligand-Mediated Plasmon-Driven Photochemical Reactions

Abstract

Contrary to the general expectation that surface ligands reduce the reactivity of surfaces by blocking the active sites, we present experimental evidence that surface ligands can in fact increase reactivity and induce important reaction pathways in plasmon-driven surface photochemistry. The remarkable effect of surface ligands is demonstrated by comparing the photochemistry of p-aminothiophenol (PATP) on resonant plasmonic gold nanorods (AuNRs) in the presence of citrate, hexadecyltrimethylammonium bromide (CTAB), and no surface ligands under visible light irradiation. The use of AuNRs with citrate and no surface ligand results in the usual azo-coupling reaction. In contrast, CTAB-coated AuNRs oxidize PATP primarily to p-nitrothiophenol (PNTP). Strong correlation has been observed between the N-O and Au-Br vibration band intensities, suggesting that CTAB influences the reaction pathway through the Br counterions that can minimize the electron-hole recombination rate by reacting with the hole and hence increasing the concentration of hot electrons that drive the oxidation reaction.

In situ surface-enhanced Raman scattering shows ligand-enhanced hot electron harvesting on silver, gold, and copper nanoparticles

“…The ligands may also have further roles, including the impairment of charge-carrier recombination [22,58], directly serving as electron donor [59], the change of LSPR band width that is related to the chemical induced damping (CID) process [10], and formation of a photosensitive metal-ligand complex as has been discussed in the case of silver nanoparticles [22]. The data discussed here, therefore, extend the previous discussion [22] of the mechanism of the six-electron reduction as follows:…”

2D Vibrational Exciton Nanoimaging of Domain Formation in Self-Assembled Monolayers

“…IR s -SNOM offers a field of view that spans micrometers while being sensitive to heterogeneity across many domains as well as intermolecular dipole coupling within domains. We studied the SAM of 4-nitrothiophenol (4-NTP) as a model system because of its relevance in photochemical reactions. ,, It is characterized by a distribution of lying-down and standing-up phases characteristic of short-chain alkanethiols and thiophenols, as shown in Figure B,C. We accomplish domain size imaging by first evaluating the vibrational coupling of the NO 2 symmetric stretch in 4-NTP SAMs with controlled density of the vibrational probe through dilution with thiophenol.…”

“…We studied the SAM of 4-nitrothiophenol (4-NTP) as a model system because of its relevance in photochemical reactions. 4,11,12 It is characterized by a distribution of lying-down and standing-up phases characteristic of short-chain alkanethiols 13 and thiophenols, 10 real-space imaging of domain size is beyond the nominal spatial resolution limit of s-SNOM, we indirectly infer the domain sizes ranging from 3 to 12 nm across a field of view representative of the whole sample. 4-NTP (Figure 1C, left) (Sigma-Aldrich, lot no.…”

Robust Charge Transfer Plasmons in Metallic Particle–Film Systems

“…The changes of the plasmonic response of the nanostructure become particularly strong if the substrate is metallic, due to the coupling with the conduction electrons of the latter, − which results in an extraordinary electric field concentrated in the gap separating the two systems. − This field enhancement is particularly large when molecular spacers on the nanometer scale are used . Due to this effect, coupled metallic particle–film structures have been the subject of extensive research in recent years − as a promising platform for achieving ultrasensitive molecule detection, − single molecule optomechanics, strong coupling, enhanced emission, − and color printing …”