Solvation Dynamics at the Water/Zirconia Interface:  Molecular Dynamics Simulations

• Published in: The journal of physical chemistry. B 2004-12, Vol.108 (51), p.19687-19697
• Main Authors: Martins, Lucimara R, Skaf, Munir S, Ladanyi, Branka M
• Format: Article
• Language: English
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp0470896

We report the results of a molecular dynamics (MD) simulation study of solvation dynamics associated with electronic excitation of the coumarin 343 (C343) dye at the interface of water and zirconia (ZrO2). We use an all-atom representation of the species present in this system. The ZrO2 partial charges and C343 geometries and charge distributions in the ground and excited electronic states have been obtained from electronic structure calculations. Our work is inspired by recent time-resolved fluorescence experiments involving C343 adsorbed at the surface of zirconia nanoparticles dissolved in H2O and D2O (Pant, D.; Levinger, N. E. J. Phys. Chem. B 1999, 103, 7846). In addition to simulation of solvation dynamics, we investigate the structure and dynamics of the dye and water in the presence of a planar ZrO2 interface. We also address several issues relevant to the interpretation of experiments, including the solvent isotope effects and the ionization state of the carboxylate group of C343 on solvation dynamics. We find that the neutral form (C343) of the dye is more strongly adsorbed at the ZrO2 interface and that the water portion of the solvation response for this form of the dye is significantly faster than for the deprotonated form, C343-. We also find that D2O−H2O solvent isotope effects on the solvation response of either form of the dye are quite modest and independent of the presence of zirconia. Rotational motion of the solute relative to the ZrO2 surface contributes a significant, very slowly relaxing component to the interfacial solvation dynamics. We discuss the implications of our findings for the interpretation of the experimental data.