A series of electrochemically generated polymeric nickel (II) Schiff base complexes was investigated by in situ electron spin resonance (ESR)/ultravioIetvisiblenear infrared (UVvisNIR) spectroelectrochemistry and the combination of cyclic voltammetry and quartz crystal microbalance (QCM) techniques. The comparative analysis of the in situ ESR and UVvisNIR (including low-energy NIR range) spectra of poIy-[Ni(Schiff)] films recorded during their oxidation at ambient temperature was performed, which allowed us to monitor the formation of different charge carriers in the polymer at different doping levels and elucidate their structure as well as the extent of their derealization. The polymer doping level achieved by its oxidation within selected range of potentials was determined by combining the results of cyclic voltammetry and QCM measurements. The influence of the substituents in the diamine backbone and phenolate moieties of the ligand on the spectroscopic properties of the oxidized polymers and number of electrons per monomer unit exchanged in the redox processes was studied in detail. Integration of data from all techniques allowed us to propose the existence of both inter- and intrachain derealization of radical cations generated in the doped polymers and show that the highest doping levels (up to two positive charges per a monomer unit) are attained in the poIy-[Ni(Schiff)] films with highly localized biphenoxyl radical cations. (C)2018 Elsevier Ltd. All rights reserved.