The transfer mechanism of 1-pyrene sulfonate anion (PSA−) across the polarized water 1,2-dichloroethane (DCE) interface was investigated by a combination of electrochemical techniques and potential modulated fluorescence (PMF) spectroscopy under total internal-reflection. The dependence of the cyclic voltammogram and the ac voltammogram on the PSA− concentration showed an apparent reversible ion transfer process. However, the PMF responses exhibited a complex dependence on the PSA− concentration, revealing adsorption and dimerization processes taking place at the interface. Analysis of the dynamic spectroelectrochemical responses suggests that PSA− is adsorbed at the interface prior to the transfer step. Upon transferring to the organic phase, PSA− appears to accumulate at the interface undergoing a dimerization reaction.