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

Abstract

Deep eutectic solvents (DESs) are novel environment-friendly media for a variety of applications. In order to obtain insight into the structure and dynamics of some less-explored DESs comprising ethylene glycol and tetraalkylammonium bromide salts with variable alkyl chain length, we have captured complete dynamics occurring in these solvents in a timescale of few femtoseconds to several nanoseconds by monitoring the time-dependent fluorescence Stokes shift of coumarin 153 employing a combination of time-correlated single-photon counting and fluorescence upconversion techniques. The solvent response function constructed from the measured data reveals a sub-picosecond component (∼0.8 ps, 20–35%) in addition to a slow component (180–475 ps) with a distribution of relaxation time. The slow time component is found to be strongly dependent on the viscosity of the medium, indicating that it arises from the diffusive motions of the solvent constituents into and out of the solvation shell, whereas the ultrafast time component, which is nearly independent of the solvent viscosity, arises from fast local motions of the constituents in the immediate vicinity of the solute molecule.

Deep Eutectic Solvents: A Review of Fundamentals and Applications

“…In most work to date, the early part of the solvation dynamics for time-dependent Stokes shifts could not be captured because the subpicosecond relaxation components were too fast relative to the limited time-resolution (typical fwhm for the instrument response function is ≈25–85 ps), resulting in “missing” components where the estimated missing amplitudes may easily be as large as 50–75%. Using an approach similar to that previously employed to study ILs, the Biswas and Samanta groups have recently coupled time-correlated single-photon counting with fluorescence up-conversion measurements to capture the complete solvent dynamics of acetamide + LiX (X = Br – , NO 3 – , ClO 4 – ) and 1:3 tetraalkylammonium bromide:ethylene glycol DESs, respectively. In both cases, a significant ultrafast (subpicosecond) solvation response was detected.…”

“…428 In most work to date, the early part of the solvation dynamics for time-dependent Stokes shifts could not be captured because the subpicosecond relaxation components were too fast relative to the limited time-resolution (typical fwhm for the instrument response function is ≈25−85 ps), resulting in "missing" components where the estimated missing amplitudes may easily be as large as 50−75%. Using an approach similar to that previously employed to study ILs, 429 the Biswas 430 and Samanta 431 tively. In both cases, a significant ultrafast (subpicosecond) solvation response was detected.…”

Interplay of conformational relaxation and hydrogen bond dynamics in the excited states of fluorescent Schiff base anions

“…Fast decays at the blue end and corresponding rise times in the red end are commonly associated with solvation dynamics. 46,56,[58][59][60][61][62] Indeed, the time resolved emission spectra (TRES) of salampy À in EtOH (Fig. 3c) exhibit a TDFSS up to 50 ps.…”

Solute dynamics of a hydrophobic molecule in a menthol–thymol based type-V deep eutectic solvent: effect of composition of the components

“…It can be seen that the spectra do not show any change in the spectral features (expect modulation in the absorption and emissions maxima) from that of conventional dipolar solvents, 23 ionic liquids 24,25 and DESs. [26][27][28] C153 is a well-known solvatochromic probe whose absorption and emission peaks are sensitive to the polarity of the solvent because of the large change in dipole moment upon excitation. 29 From the absorption and emission spectra of C153 in type-V DES (Fig.…”