Literature data on the electron-acceptor properties of poly(diphenylene phthalide) (PDP) and poly(diphenylene sulfophthalide) (PDSP) are briefly generalized. Different types of electron affinity (EA) are calculated (in eV) in the B3LYP/6-311+G(d,p) approximation for model compounds of diphenyl phthalide (DPP) and diphenyl sulfophthalide (DPSP): vertical EAver = 0.21 and 0.06, adiabatic EAad = 0.66 and 0.58, and effective (taking into account the С—О bond cleavage in the phthalide and sulfophthalide cycles) EAeff = 1.21 and 2.21, respectively. The activation energies of the С—О bond cleavage in the phthalide and sulfophthalide cycles in radical anions (RAs) of DPP and DPSP are 0.34 and 0.07 eV, respectively. In reactions with alkaline metal atoms (Li and Na), the ring opening in DPSP occurs without a barrier, while in DPP the barrier is 0.34 and 0.31 eV for ring opening by the Li and Na atoms, respectively. The easiness of opening of the sulfophthalide ring compared to the phthalide one is the main reason for a longer lifetime of DPSP RA relatively to electron autodetachment compared to the the DPP RA (which was found earlier by negative ion mass spectrometry) and for dissociative PDSP reduction chemistry with formation of distonic RA. The high dipole moments of the phthalide (∼5 D) and sulfophthalide (∼6 D) fragments of the studied polymers provide a basis for the formation of physical dipole traps in them. The EA were calculated for the compounds modeling defect and end groups in PDP and PDSP. Macromolecules of PDP and PDSP are considered as a system of physical dipole and chemical electron traps related to the main, defect, and end electron-acceptor groups of the polymers. In the case of PDP, the EA of the anthraquinone end groups (AEGs) significantly exceeds the affinity of the main phthalide fragments, and the presence of AEGs should be taken into account when considering the reductive, electroactive, and luminescence properties of PDP. According to the calculations, the biphenyl fragments have the lowest ionization potentials (IP) among all structural units of the PDP and PDSP chains. A significant increase in the EA and a decrease in the IP of the triplet states of the model compounds indicate the possibility of participation of the triplet states of the PDP fragments in the charge separation and prolonged recombination photoluminescence observed in this polymer. In the framework of the polarizable continuum model (PCM), the influence of the solvents (DMSO and DMF) and polymer environment on the values of EA and IP of singlet and triplet states was estimated for the most analyzed model compounds. The electron-acceptor properties of the compounds modeling the chemically modified polymer units, radicals and carbocations of the triarylmethyl type, were considered. The experimental manifestations of electron traps were considered: the electronic and ESR spectra of the corresponding RAs, including AEG RAs. The possibility of participation of electron traps in the formation of the volume charge and in the electroactive phenomena in PDP (as transport units) was discussed. Phthalide ring opening in PDP in reactions involving electron seems to be poorly probable, and AEGs play an important role in these reactions.