Rational design and tailoring of ionic liquids and deep eutectic solvents: from homologous heterogeneity to preparation-controlled applications

Abstract

Ionic liquids (ILs) and deep eutectic solvents (DESs) have emerged as alternative green systems capable of breaking through the limitations of traditional solvents, yet their ambiguous classification boundaries have long hindered their industrial application. Through multidimensional empirical analysis, this review systematically elucidates the fundamental distinctions between ILs and DESs. This review is the first to establish a component intersection database, revealing a significant homologous heterogeneity phenomenon between ILs and DESs sharing identical chemical compositions. We propose a classification theory that the “preparation method determines the dominant intermolecular interaction type and thus defines the classification”. The differentiation in preparation methods leads to a divergence in their core interaction forces, thereby resulting in distinct performances across various applications. Moreover, we innovatively propose IL-based DESs (IDESs) as critical species evidence. Using ILs as raw materials, a hydrogen bond-dominated architecture is successfully constructed via the typical DES preparation route. This system is explicitly classified as a DES, thereby providing practical mutual validation of the independence of these two solvents. This review offers new theoretical support for resolving the classification controversy between ILs and DESs, and the green solvent database established provides a practical tool for precise solvent selection in industrial applications.