The electrochemical character of 1,4-naphthoquinone (Q) in aprotic media and proton donor mixed solvent was explored by cyclic voltammetry (CV), in situ FT-IR spectroelectrochemistry, cyclic voltabsorptometry (CVA) and derivative cyclic voltabsorptometry (DCVA) techniques. In dimethyl sulfoxide (DMSO), Q is reduced in normal two-step one-electron transfer, forming the anion radical (Q center dot(-)) in the first step and the dianion (Q(2-)) in the second step accordingly. However, the electrochemical behavior of Qin acetonitrile (CH3CN), acetonitrile-ethanol mixed solvent and dimethyl sulfoxide-ethanol mixed solvent is different from that in DMSO. It is found that in these solvents, Q is reduced to firstly and meanwhile the neutral-anion radical dimer (Q(2)center dot(-)) comes into being. Then Q center dot(-) is reduced to Q(2-) and Q(2)center dot(-) is reduced to Q(2)(2-). At more negative potential, Q(2)(2-) is further reduced to Q(2)(3-). In proton donor mixed solvent, hydrogen-bonding forms between Q(2-) (Q center dot(-), Q2 center dot(-), Q(2)(2-), Q(2)(3-)) and C2H5OH. (C) 2015 Elsevier B.V. All rights reserved.