Formation of Distinct Condensed Molecular Phases at Solid-Liquid Interfaces by Plasmon-Driven Molecular Trapping under Ambient Conditions

Advancing nanoscience requires precise control of molecules at the nanoscale, especially under ambient conditions where overcoming Brownian motion remains a significant challenge. Plasmonic fields can exert optical forces strong enough to overcome thermal fluctuations at the single-molecule level, even under ambient conditions. This enables precise spatial and dynamic control over molecular condensates, owing to the inherently selective, non-destructive, remote, and energy-efficient nature of plasmonic manipulation. Herein, we employ 4,4'-bipyridine (44bpy) as a target system and monitor its two-dimensional diffusion using surface-enhanced Raman scattering (SERS) under applied optical forces through the induced plasmon field. Systematic variation of solvents and ion-pairing conditions reveals critical factors to achieve plasmon-induced molecular condensation for diffusing molecules at room temperature. The resulting condensed phase exhibits higher density exceeding that of conventional thermodynamic equilibria, indicating the emergence of a distinct adsorption phase driven by highly localized field perturbations. These findings demonstrate that plasmonic fields can direct cooperative molecular behavior via modulation of solvation and ion-pairing interactions. This study establishes plasmonic trapping as a powerful tool to create nonequilibrium molecular phases under ambient conditions, inventing the way for advanced photonic manipulation strategies.