In this region due to formation of strongly hydrogen bonded 1DMSO:2H 2O complexes, hydration around the probe C480 decreases, as a result of which solvation time increases. However, the first region is the most interesting one.

Most probably, the anomalous solvation trend in this region is fully guided by the shear viscosity of the medium. Among them, the second region (X D = 0.27–0.35) is very common as most of the thermodynamic properties exhibit deviation in this range. The results of both the methods roughly indicate that solvation time of C480 reaches maxima in the mole fraction of DMSO X D = 0.12–0.17 and X D = 0.27–0.35, respectively. We have calculated average solvation times of C480 by two individual well-known methods, among them first one is spectral-reconstruction method and another one is single-wavelength measurement method. DMSO-water binary mixture has repeatedly given evidences of its dual anomalous nature in front of our systematic investigation through steady-state and time-resolved measurements. Particularly, these studies encourage us to investigate the anomalies from experimental background. Recent molecular dynamics simulations have predicted two anomalous regions of DMSO-water binary mixture.

In this work, we have investigated the composition dependent anomalous behavior of dimethyl sulfoxide (DMSO)-water binary mixture by collecting the ultrafast solvent relaxation response around a well known solvation probe Coumarin 480 (C480) by using a femtosecond fluorescence up-conversion spectrometer.

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