Anomalous Dynamics in tert-Butyl Alcohol–Water and Trimethylamine N-Oxide–Water Binary Mixtures: A Femtosecond Transient Absorption Study

[Image: see text] In this article, we have investigated the unusual dynamics of tert-butyl alcohol (TBA)–water and trimethylamine N-oxide (TMAO)–water binary mixtures using solvation dynamics as a tool. For this purpose, femtosecond transient absorption spectroscopy has been employed. Although these two molecules are isosteres to each other, a significant difference in water dynamics has been observed. The solvation times in TBA–water binary mixtures are found to be between 1.5 and 15.5 ps. On the contrary, we have observed very fast dynamics in TMAO–water binary mixtures (between 210 and 600 fs). Interestingly, unusual retardation in dynamics is observed at 0.10 mole fraction of TBA and TMAO in both the binary mixtures.