Rational design and tailoring of ionic liquids and deep eutectic solvents: From homologous heterogeneity to preparationcontrolled applications

Abstract

Ionic liquid (IL) and deep eutectic solvent (DES) have emerged as green alternative systems capable of breaking through the limitations of traditional solvents, yet their ambiguous classification boundaries have long hindered 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 significant homologous heterogeneity phenomenon between ILs and DESs sharing identical chemical compositions. We propose a classification theory that "Preparation method determines the dominant intermolecular interaction type and thus defining 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 DES (IDES) 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 for the independence of these two solvents. This review offers new theoretical support for resolving the classification controversy between ILs and DESs, and the established green solvent database provides a practical tool for precise solvent selection in industrial applications.