Hydrocarbon Chain-Length Dependence of Solvation Dynamics in Alcohol-Based Deep Eutectic Solvents: A Two-Dimensional Infrared Spectroscopic Investigation

Abstract

Deep eutectic solvents (DESs) have gained popularity in recent years as an environmentally benign, inexpensive alternative to organic solvents for diverse applications in chemistry and biology. Among them, alcohol-based DESs serve as useful media in various applications due to their significantly low viscosity as compared to other DESs. Despite their importance as media, little is known how their solvation dynamics change as a function of the hydrocarbon chain length of the alcohol constituent. In order to obtain insights into the chain-length dependence of the solvation dynamics, we have performed two-dimensional infrared spectroscopy on three alcohol-based DESs by systematically varying the hydrocarbon chain length. The results reveal that the solvent dynamics slows down monotonically with an increase in the chain length. This increase in the dynamic timescales also shows a strong correlation with the concomitant increase in the viscosity of DESs. In addition, we have performed molecular dynamics simulations to compare with the experimental results, thereby testing the capacity of simulations to determine the amplitudes and timescales of the structural fluctuations on fast timescales under thermal equilibrium conditions.

Complete Solvation Dynamics of Coumarin 153 in Tetraalkylammonium Bromide-Based Deep Eutectic Solvents

“…29 In contrast, the ultrafast sub-picosecond component, which is nearly independent of the solvent viscosity, can be attributed to fast relaxation of the local environment created by DES constituents that arises because of only minor readjustments of the intermolecular hydrogen-bonding, positions, and orientations of the constituents present in immediate vicinity of the probe molecule within the solvation shell. 33,39,40 In order to understand the influence of alkyl chain length (or ionic radius) of the cation on the individual solvation 6c. A linear relationship between the two suggests that this slow solvation component, which arises from the diffusive movements in DESs, strongly depends on the size of cationic constituent of these solvents.…”

Probing the structural features and the micro-heterogeneity of various deep eutectic solvents and their water dilutions by the photophysical behaviour of two fluorophores

“…These studies revealed strong dynamic heterogeneity originated from modification of the H-bond network by virtue of H-bond reorientations and collective H-bond relaxations, while signatures of either mild or high spatial micro-heterogeneity were collected depending on the investigated DESs. Other studies have instead focused on the complete solvation dynamics of the solvent shell around the probes, investigated by both fluorescence and FTIR spectroscopy and supported by molecular dynamics simulations [45][46][47][48][49].…”

Electrostatic Manifestation of Micro-Heterogeneous Solvation Structures in Deep-Eutectic Solvents: A Spectroscopic Approach

“…32,40 It has been suggested that changes in the hydrocarbon chain-length of the alcohol significantly influence the properties of alcohol-based DES. 30,41 solvent interactions. To gauge solute−solvent interactions, spectroscopic responses of fluorophores have been commonly used to assess the polarity of DES through semiempirical polarity scales.…”

“…In recent times, studies have been performed to unravel heterogeneous nature of deep eutectic microstructure both from spectroscopic and computational standpoint. − The effect of the hydrogen bonding partner on DES property and its relation with nanoscale heterogeneity has been analyzed using classical MD simulation ,, and ab initio MD simulation. , Microscopic structure and solute–DES interaction are also discussed in conjunction with the polarity of the HBD partner. − A few recent interesting studies also discuss the stability of DES in the aqueous presence of water. ,, …”

“…As the choice of an appropriate DES for any given process depends on the DES solvation properties, insights into the DES solvation structures around a solute is desired. ,, Alcohol-based (as HBD) eutectic systems are used as media in various applications due to their significantly low viscosity compared to other DESs. , It has been suggested that changes in the hydrocarbon chain-length of the alcohol significantly influence the properties of alcohol-based DES. , However, little is known about how the residue specific distribution and the hydrogen bonding of the DES constituents (ChCl and alcohol) are altered by the alcohol chain length. Thus, it is critical to obtain a molecular understanding of how the solvation structures of alcohol-based DES with varying chain-lengths influence the solute–solvent interactions.…”