Viologen/eutectic solvent as well as preparation method and application thereof

The invention relates to the technical field of electrochromic material preparation, in particular to a viologen/eutectic solvent and a preparation method and application thereof. According to the invention, different quaternary ammonium salt groups are introduced on a side chain through N-alkylation reaction to synthesize a viologen derivative, and the viologen derivative is used as a hydrogen bond donor material to construct a novel multi-element eutectic solvent-viologen/eutectic solvent together with hydrogen bond donor materials such as ethylene glycol, choline chloride or glycerol and choline chloride. Different side chain groups endow the viologen derivative with changeable color changes and stronger sunlight modulation capability, the prepared electrochromic device can be reversibly switched among 3-4 or more colors, is almost completely lightproof in a coloring state, can meet various requirements of users on sunlight transmittance, privacy, color comfort and the like in different scenes, and has wid