The properties of p-phenylenediamine- (PD-) based systems substantially depend on the molecular topology. The singly bridged PD analogues HMPD and OMPD in which the PD rings are connected by a flexible linker reveal particular electronic properties in their radical cations and dications. The EPR and UV-vis spectra of HMPD2+center dot center dot were found to be exceptionally temperature-sensitive, following a change from the extended conformation (doublet-doublet state) predominant at room temperature to, the pi-stacked conformation (singlet state) prevailing at dry-ice temperature. Changing the single bridge from (CH2)(3) to dimethylated CH2CMe2CH2 in OMPD2+center dot center dot causes considerably less of the g-stacked conformation to be present at low temperature as a result of the steric interactions with the methyl groups of the bridge. In contrast to HMPD2+center dot center dot and OMPD2+center dot center dot, in which the positive charges are localized separately in each PD+center dot ring, in the extended conformation, exchange of the electron ("hole hopping") between the two PD units (fast at the time scale of EPR experiments) was observed for HMPD+center dot and OMPD+center dot. This process slows in a reversible manner with decreasing temperature, thus forming the radical cation with the unpaired electron spin density predominantly on one PD core, at low temperatures. Accordingly, a subtle balance between conformational changes, electron delocalization, and spin states could be established.