Given that the properties of DSILs depend strictly on the molar ratio between constituents, in this study, we attempted to further elucidate the phenomenon of synergistic action for DSILs for agrochemical applications and to find the optimal molar ratio of the parent ILs that will provide the most favorable properties. We also provide a detailed spectral and physicochemical characterization of the new DSILs, as well as a preliminary evaluation of their aqueous toxicity toward a model freshwater alga, Chlorella vulgaris.