This paper reports results from temperature and composition dependent steady state UV-Visibleabsorption and fluorescence measurements and time-resolved fluorescence experiments, using a dipolar probecoumarin 153 (C153), in TMU/water binary mixtures.Q1Both steady state and time-resolved spectroscopic dataindicate, much like in water/alcohol mixtures, TMU-induced structural stiffening and transition of the tetrahedralH-bond network of water. The structural transition referred to above means cosolvent-induced transitionof three dimensional tetrahedral H-bond network to two dimensional zig-zag chain-like structure often foundin alcohols. A comparison to the results obtained for aqueous alcohol solutions suggests that the cosolvent concentrationat which the structural transition occurs depends both on the polarity of the cosolvent and the size ofthe cosolvent molecules. UV-Visible absorption measurements reveal aggregation among TMU molecules atlower TMU concentration which shows a temperature maximum. In addition, red edge excitation effects havebeen observed at very dilute TMU concentration suggesting distribution of C153 among heterogeneous environments.All these results indicate hydrophobic interaction-induced aggregation of TMU in dilute aqueoussolutions which corroborate well with the existing simulation observation.
Volume 134, 2022
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