A series of thiophene-2,5-dicarboxylic acid diesters ( R–Th , compounds 3 – 9 ) with linear and branched alkyl ( 3 – 7 ) and benzyl ( 8 , 9 ) ester groups have been synthesized and characterized by 1 H/ 13 C NMR and MS. Their electrochemical reduction in cyclic voltammetry experiments proceed as two-step single-electron transfer process to form radical anions R–Th •– (at −1.87 … −2.00 V vs Ag/Ag + ) and dianions R–Th 2– (at −2.48 … −2.68 V vs Ag/Ag + ). In spectroelectrochemical experiments in Bu 4 NClO 4 / N,N -dimethylformamide electrolyte solution, all compounds exhibit reversible color changes from colorless in their neutral state to blue colors in the reduced state, with two characteristic absorptions of radical anions R–Th •– in the short-wavelength ( ca. 406–420 nm) and long-wavelength regions ( ca. 610–655 nm). The L*a*b* CIE color coordinates of th e sandwich-type electrochromic devices have been evaluated by colorimetry measurements and the devices demonstrated good coloration efficiency of up to 512 cm 2 C −1 . The cycling stability of the materials on electrochromic coloring/bleaching substantially depends on the structure of the R ester groups and increased with increasing the steric hindrances in the R. In the series of seven studies compounds, the best cycling stability was observed for R = 2-ethylhexyl and benzyl. The degradation mechanism during electrochromic cycling in an inert atmosphere (under nitrogen) and in air is discussed. • Cathodic electrochromism (colorless to blue) with a high contrast. • Thiophene-2,5-dicarboxylic acid diesters as electrochromic materials. • An effect of the ester groups on the contrast and cycling stability of ECD devices. • Radical anions and their stability. • The mechanism of ECD devices degradation, reactions with superoxide.