The Pivotal Role of Hot Carriers in Plasmonic Catalysis of C−N Bond Forming Reaction of Amines

Abstract

Here, we demonstrate the simultaneous utilization of both the hot carriers (electrons and holes) in the photocatalytic transformation of benzylamine to N‐benzylidenebenzylamine and the scope of reaction has also been successfully demonstrated with catalytic oxidation of 4‐methoxybenzylamine. The wavelength‐dependent excitation of AuNP allows us to tune the potential energy of charge carriers relative to the redox potential of the reactants which leads to energetically favorable product formation on the nanoparticle surface. We capture the formation of reaction intermediates and products by using in situ Raman spectroscopy, complemented by NMR spectroscopy and GC‐MS. Based on the experimental substantiations, a plausible reaction mechanism has been proposed.

Efficient Extraction of Energetic Charge Carriers from an Engineered Plasmonic Nanocomposite to Perform Cascade Reactions

“…The temperature increase for the AuÀ Pt NCs system due to light irradiation was estimated to be a few μK (see section S5c of supporting information), which is in line with the other literature reports. [3,56] This order of temperature increase cannot explain the observed trend. Moreover, our wavelength-dependent study clearly shows that the reaction is mostly charge carrierdriven and not photothermal driven.…”

Plasmonic Photocatalysis: Activating Chemical Bonds through Light and Plasmon

“…In a recent study by Chandra and co‐workers, a simultaneous utilization of both hot electrons and hot holes in photoexcited AuNPs was achieved for the CN bond formation, by the oxidative amine coupling without the use of any hole/electron scavenger or support. [ 132 ] The authors reported for the first time the use of AuNP as both the light absorber as well as the catalyst to drive oxidative coupling of amine to imine at ambient conditions. The reaction was carried out using AuNPs as the sole plasmonic photocatalyst with benzylamine as the hot hole acceptor and atmospheric O 2 as the hot electron acceptor, under visible light excitation (Figure 8c).…”

“…In such conditions, the reaction rate will be proportional to the scavenging power of sacrificial agents, which essentially depends on the difference between the energy levels of the sacrificial agent and the plasmonic photocatalyst: higher the difference, higher the scavenging power, and thus higher the reaction rate. [ 38,132,173 ] Figure 10c shows the energy levels of commonly used hole scavengers in photocatalysis, with respect to the Fermi energy of AuNPs. As can be seen from the energy level diagram, alcohols have higher oxidation potential than water, which means the former is a better hole scavenger.…”

“…One of the well-accepted experiments involves wavelength-dependent studies, which will trigger different excitation pathways and a direct impact of it can be observed on the reaction rate: for hot charge carrier dominated reactions, a higher rate is expected under interband excitation compared to intraband excitation. [37,38,112,120,132] A proper choice of nanomaterial, such as gold nanorods, will allow the selective excitation via inter or intraband transitions, which can help in deconvoluting the roles of hot-charge carriers and photothermal effects. [169,170]…”

“…In such conditions, the reaction rate will be proportional to the scavenging power of sacrificial agents, which essentially depends on the difference between the energy levels of the sacrificial agent and the plasmonic photocatalyst: higher the difference, higher the scavenging power, and thus higher the reaction rate. [38,132,173] Figure 10c shows the energy levels of commonly used hole scavengers in photocatalysis, with respect to the Fermi energy The local thermal effects can be minimized by controlling the flow dynamics. A colloidal photocatalytic system will experience minimal thermal effects compared to a bed-reactor (or in solid state), because the natural convection will result in the faster dissipation of heat from the NP surface in the colloidal system.…”