Communication: The mechanism of charge delocalization in mono- and dianions of differently substituted oligo(p-phenylenes) has been studied by absorption spectroscopy. Poly(p-phenylene) is of great interest in this respect, but is experimentally inaccessible because of its complete insolubility and infusibility, so data on more soluble oligomeric systems that are structurally related to the polymer have to be used to extrapolate towards the behavior of the polymer. Results from UV/vis/NIR spectra and cyclic voltammetry are reported that allow the influence of substituents on the conjugation length to be reliably predicted.