Time-dependent fluorescence in nanoconfined solvents: linear-response approximations and Gaussian statistics

Area of Science:

• Chemical Physics
• Computational Chemistry
• Materials Science

Background:

• Understanding solvation dynamics is key to chemical reactions and molecular processes.
• Nanoconfinement significantly alters solvent behavior compared to bulk systems.
• Linear-response theories and statistical assumptions are common approximations for solvation dynamics.

Purpose of the Study:

• To test the validity of dynamic and static linear-response theories for solvation dynamics.
• To evaluate the accuracy of assuming Gaussian statistics in nanoconfined environments.
• To compare simulation results with theoretical approximations for a model dye in confined acetonitrile.

Main Methods:

• Nonequilibrium molecular-dynamics simulations were performed.
• Time correlation functions were calculated from equilibrium simulations.
• The normalized dynamic Stokes shift and dye molecule position were analyzed.

Main Results:

• Dynamic linear-response theory showed limitations in describing solvation dynamics.
• The assumption of Gaussian statistics provided results consistent with full nonequilibrium simulations.
• Accuracy was assessed for spherical hydrophobic cavities of varying radii (12, 15, 20 Å).

Conclusions:

• Gaussian statistics offer a reliable approach for modeling solvation dynamics in nanoconfined solvents.
• Dynamic linear-response theory approximations may not be universally applicable in confined systems.
• The study highlights the importance of statistical assumptions in computational chemistry.