Characterizing Counterion-Dependent Aggregation of Rhodamine B by Classical Molecular Dynamics Simulations

Area of Science:

• Materials Science
• Computational Chemistry
• Physical Chemistry

Background:

• Dye aggregation significantly impacts optical properties.
• Counterions play a crucial role in controlling dye self-assembly and structure.
• Fluorinated counterions like F5TPB can enhance Rhodamine B (RB) aggregation into nanoparticles.

Purpose of the Study:

• To develop a classical force field (FF) for modeling Rhodamine B (RB) and F5TPB self-assembly in water.
• To understand the atomistic details of how counterions influence RB aggregation and optical properties.
• To validate the FF's accuracy against experimental observations.

Main Methods:

• Development of a classical force field based on generalized Amber parameters.
• Classical molecular dynamics (MD) simulations of RB/F5TPB systems in water.
• Comparison of simulation results with experimental data on fluorescence quantum yield (FQY).

Main Results:

• The re-parametrized FF successfully reproduced nanoparticle formation in RB/F5TPB systems.
• Simulations showed only RB dimeric species formed with iodide counterions.
• Atomistic insights revealed the F5TPB counterion acts as a spacer, influencing aggregate structure and fluorescence quenching via H-type RB-RB dimers.

Conclusions:

• The developed classical FF enables reliable modeling of dye aggregation in RB-based materials.
• Counterion choice is critical for controlling dye self-assembly and resultant optical characteristics.
• The study provides a computational tool for designing advanced dye materials with tailored properties.