Nanostructured metallic or heavily doped semiconductor materials have attracted significant attention over the last decade due to their unique ability to overcome the optical diffraction limit, concentrating light into sub-wavelength or even sub-nanometer volumes. This capability has given rise to a flourishing field known as plasmonics, which explores the distinctive optical properties and applications of plasmonic nanostructures. Recently, this field has expanded from plasmonic physics to plasmonic chemistry, primarily investigating the interactions between plasmons and molecules. When a plasmonic nanostructure is excited, it can collect photons over a region larger than its physical size and concentrate the incident light into extremely confined regions around the nanostructure. This leads to electromagnetic near-field enhancement. During the excitation process, the plasmonic nanostructure redistributes and converts the photon energy into excited carriers and heat, thereby altering energy distribution in both time and space. In summary, plasmonic nanostructures can dynamically redistribute photons, electrons, and heat across various temporal and spatial scales, producing three primary physical effects: localized electromagnetic field enhancement, generation of excited carriers, and photothermal effects. These capabilities offer new possibilities for driving chemical reactions using localized photon, electronic, and/or thermal energies. Plasmon-mediated chemical reactions (PMCRs) have become a promising approach for facilitating light-driven chemical reactions by utilizing solar energy, showing distinct differences from and potential advantages over traditional thermochemistry, photochemistry, and photocatalysis. Firstly, plasmonic nanostructures can concentrate incident light or extend light paths, enhancing chemical reactions or increasing the excitation of other materials, such as semiconductors or dyes, within specific regions. The enhanced electromagnetic field on the surface or interface induces surface excitation, effectively minimizing electron-hole recombination by circumventing charge migration from the bulk to the surface. Secondly, the excited carriers can transfer to molecules, activating reactants by creating charged states that may follow new potential energy surfaces, altering reaction pathways. Thirdly, the energy distribution of the excited carriers can be fine-tuned by adjusting the geometry or aggregation state of the nanostructures, and the optical properties of plasmonic nanostructures can be tuned to span nearly the entire solar spectrum. Finally, as nanoscale sources of heat, plasmonic nanostructures can confine thermal fields within nanometric volumes, creating significant thermal gradients that enhance heating dynamics and efficiency, increasing chemical reaction rates. In the past decade, numerous PMCRs have been reported, encompassing exothermic reactions such as catalytic oxidation, organic synthesis, and hydrogenation, as well as endothermic reactions such as CO₂ reduction and water splitting. Plasmonic chemistry offers a promising strategy for driving chemical processes under relatively mild conditions.

The typical applications of plasmons, including photothermal therapy, desalination, photodetection, molecular detection, molecular manipulation, and PMCRs, as well as the primary effects utilized in these applications, are summarized. The excitation and relaxation processes of plasmons are systematically discussed, covering the generation and conduction of heat, as well as the creation and relaxation of plasmonic hot carriers. Typically, the relaxation process of plasmons can be divided into several components that occur on different timescales. Furthermore, as PMCRs are one of the few applications simultaneously influenced by the three primary effects of plasmons—localized electromagnetic field enhancement, excited carriers, and photothermal effects—we explore the chemical reactions induced by these three effects separately. An integrated framework for PMCRs is established, taking into account time, space, energy, and probability. Notable PMCR systems are introduced, such as catalytic oxidation reactions that are significantly accelerated by Ag plasmonic nanoparticles under low-intensity visible light and water splitting driven by plasmon-excited electrons and holes from Au nanorod arrays under visible light. Concurrently, the unique characteristics and potential advantages of PMCRs compared to traditional thermochemistry, photochemistry, and photocatalysis are discussed, including localized regions and the induction of nonlinear photoexcitation under low-intensity incident light. However, due to the lack of a bandgap, plasmon-excited carriers typically have very short lifetime, which significantly reduces the possibility of charge transfer from plasmonic nanostructures to molecules, thus limiting the improvement of reaction efficiency. Despite this, the mechanism of PMCRs can be explained through thermochemistry, photochemistry, and/or photocatalysis, although it is more complex due to the coupling of localized multi-fields. After systematically discussing the key features of various plasmon effects and their main roles in mediating reaction processes, we suggest future directions and address challenges across six aspects to fully exploit the potential of PMCRs.

Plasmons offer a unique opportunity to explore light-molecule interactions or even drive chemical reactions through localized photon, electronic, and/or thermal energies. Although significant effort is still required to achieve a comprehensive physicochemical understanding of PMCRs and advance towards commercialization, PMCRs have demonstrated considerable potential as a novel reaction mode distinct from traditional thermochemistry, electrochemistry, and photochemistry, providing an effective approach for mediating chemical processes.