Three types of bithiophene-fused benzo[c]phospholes were successfully prepared by TiII-mediated cyclization of the corresponding dialkynylated bithiophene derivatives as a key step. Each σ3-phosphorus center of the benzo[c]phosphole subunits was readily transformed into σ4-phosphorus center by Au coordination or oxygenation. In addition, the bithiophene subunit was functionalized at the α,α′-carbon atoms by Pd-catalyzed cross-coupling reactions with heteroarylmetals and by an SNAr reaction with hexafluorobenzene. The experimentally observed results (NMR spectroscopy, X-ray analysis, UV/Vis absorption/fluorescence spectroscopy, and cyclic/differential-pulse voltammetry) have revealed that the structural, optical, and electrochemical properties of the bithiophene-fused benzo[c]phospholes vary considerably depending on the π-conjugation modes at the bithiophene subunits and the substituents of the heterocyclopentadiene components. The appropriately ring-annulated σ3-P derivatives and σ4-P-AuCl complexes were found to emit fluorescence in the orange–red region, and the σ4-P-oxo derivatives proved to undergo reversible one-electron reduction at −1.4 to −1.8 V (vs ferrocene/ferrocenium). These results indicate that the bithiophene-fused benzo[c]phospholes possess narrow HOMO–LUMO gaps and low-lying LUMOs, which was confirmed by density functional theory calculations of their model compounds. The time-of-flight measurement of an ITO/benzo[c]phosphole/Al device showed that the electron mobility in the P-oxo derivative is one-order higher than that in Alq3 at low electric fields. The present study demonstrates that the arene-fused benzo[c]phosphole skeleton could be a highly promising platform for the construction of a new class of phosphole-based optoelectrochemical materials.