Unraveling the Dynamics and Microheterogeneity of Deep Eutectic Solvents: Insights from 2D IR Spectroscopy and Molecular Simulations

Deep eutectic solvents (DESs), composed of both hydrogen bond donors and acceptors, have evolved into a versatile family of viscous fluids with wide-ranging applications across multiple fields. DESs are known for their ability to generate nanoscale spatial heterogeneities, giving rise to intricate nanodomains interwoven with complex hydrogen bond networks. Understanding the role of viscosity in DESs is crucial, as it is a well-established factor influencing their dynamics, and this understanding is key to fully realizing their potential. We compare solute reorientation timescales and spectral diffusion timescales obtained from two-dimensional infrared spectroscopy with results from molecular dynamics simulations. This comparative analysis highlights the significant role played by inter-component hydrogen bond dynamics within the nanodomains, providing valuable insights into the determination of domain-specific microviscosity within DESs. Furthermore, we investigate how microheterogeneity within DESs evolves by varying the hydrogen bond donors and the mixing composition. Additionally, we explore the impact of introducing water, shedding light on the disruption of hydrogen bond networks in these heterogeneous nanodomains. This investigation promises to advance our understanding of DES behavior and paves the way for novel applications across a spectrum of scientific disciplines.