The aim of this theoretical study is to provide an in-depth interpretation of the UV-vis absorption spectra and electrochemical data of two series of 2,5-dipyridyl- and 2,5-dithienylphosphole derivatives containing sigma(3)- or sigma(4)-P atoms. The geometric and electronic structures of those phosphole-containing pi-conjugated systems were investigated using density functional theory (DFT). To assign the absorption peaks observed in the UV-vis absorption spectra, we computed the energies of lower-lying excited states within the adiabatic approximation of time-dependent DFT (TDDFT). All DFT calculations were performed using the B3LYP functional and the split valence plus polarization SV(P) basis set. To elucidate structure-property relationships, we studied in a systematic way the influence of different structural modifications on the electronic structure and emphasized the corresponding consequences for the electrochemical and optical properties. More specifically, we considered successively the influence of pyridyl and thienyl substituents at the alpha-position, flattening of the P atom, oxidation of the P atom by elemental sulfur, and fusion of a saturated six-membered ring onto the phosphole core.