Uncovering the Role of Chemical and Electronic Structures in Plasmonic Catalysis: The Case of Homolysis of Alkoxyamines

The local surface plasmon resonances of gold nanoparticles have the potential to create alternative pathways for organic chemical reactions. These transformations depend on various physical factors, such as the temperature, illumination regime, and nanoparticle type. However, the role of chemical factors associated with organic reactants, including the molecular structure, electronic effects, and bonding with the metal surface, is often underestimated. To explore the role of these chemical factors, we synthesized five alkoxyamines (AAs) with different chemical and electronic structures and used electron paramagnetic resonance spectroscopy to study the kinetics of plasmon-induced homolysis. The kinetic data revealed that the rate constant (kd) for plasmon-assisted homolysis is dependent on the highest occupied molecular orbital (HOMO) energy of the AAs, which cannot be described by the kinetic parameters or activation energies observed in thermal homolysis experiments. The proximity of the HOMO to the Fermi energy (Ef) of Au led to a more active decrease in the energy required to excite the adsorbate. The observed trend in kd indicates that the intramolecular excitation mechanism plays a key role instead of other commonly accepted mechanisms, which is supported by DFT calculations, spectroscopic characterization, and numerous control experiments. The intramolecular excitation mechanism is the most relevant explanation for the plasmon-induced homolysis of AAs. This observation suggests that the electronic structures of the organic molecules may play a key role in other related reactions used to study the mechanisms of plasmon catalysis.