Probing the Dynamics of Plasmon–Molecule Hybrid Systems via Ultrafast Spectroscopy

Plasmon–molecule hybrid systems represent a frontier in photocatalysis, enabling efficient charge separation and energy conversion through strong electronic coupling between metallic nanoparticles and molecular components. Herein, the photophysical dynamics of hybrid systems formed by gold nanoparticles functionalized with aromatic thiol ligands using ultrafast transient absorption spectroscopy is probed. A solvent‐dependent analysis of the phonon–phonon decay lifetime as a sensitive probe of charge delocalization and hybridization strength is introduced. The results reveal consistent elongation of phonon–phonon relaxation times upon ligand attachment, indicating the formation of delocalized hybrid states and providing robust evidence of coherent plasmon–molecule interactions. Despite solvent‐induced complexities that obscure expected dielectric trends, the persistence of extended lifetimes across multiple environments underscores the role of strong hybridization in modulating charge dynamics. This work establishes phonon–phonon relaxation as a valuable fingerprint for hybridization and offers critical insights for designing tailored plasmonic materials to optimize charge transfer in catalytic and energy conversion applications.