Two series of cationic gemini compounds have been studied with respect to electrochemical and via filling behaviors in copper electrodeposition. They include linear and pyridinium gemini series. The investigation focuses on the structural aspect of the spacer and the hydrophobic tails of the geminis. The electrochemical and via filling behaviors of the geminis are strongly influenced by their chemical structure. The type and the length of the spacer of geminis are of major importance for their suppressing capability and the via filling behavior. Gemini molecules response to SPS (bis(3-sulfopropyl) disulfide) shows structure dependence. The change of Lambda(eta) (the potential difference obtained from different rotational speed) values of the geminis upon adding SPS depends mainly on the structure of the hydrophobic tails of the gemini molecules. SPS may improve the via filling behavior for the geminis with flexible hydrophobic tails, while it may lead to a reduced via filling activity for those with the rigid hydrophobic tails. Potential oscillation in the galvanostatic experiment can be associated with the rigidity of the hydrophobic tails of geminis. (C) 2016 The Electrochemical Society. All rights reserved.