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

Abstract

Advancing nanoscience demands precise control of molecules at the nanoscale, particularly in ambient conditions where Brownian motion predominates. Plasmonic fields can generate optical forces strong enough to overcome thermal fluctuations at the single-molecule level, even under ambient conditions. This enables spatially and temporally precise control over molecular condensates through the inherently selective, non-destructive, remote, and energy-efficient nature. Here, we utilize 4,4'-bipyridine (44bpy) as a target system and monitor its two-dimensional diffusion using surface-enhanced Raman scattering (SERS) under the influence of optical forces generated by the plasmon field. Systematic variation in solvents and ion-mediated interaction reveals critical factors for achieving plasmon-induced molecular condensation for diffusing molecules at room temperature. The resulting condensed phase exhibits higher density than that formed under conventional thermodynamic equilibrium, highlighting the emergence of a distinct adsorption phase driven by highly localized field perturbations. These findings demonstrate that plasmonic fields possess the capacity to regulate cooperative molecular behavior via modulation of solvation and electrostatic interaction. This study establishes plasmonic trapping as a formidable technique to create nonequilibrium molecular phases under ambient conditions, thereby facilitating the development of innovative strategies for molecular manipulation.