The synthesis and optical properties of several phosphorescent conjugated poly(phenylene)s containing cyclometalated square-planar platinum (II) complexes are reported. These electronic polymers were synthesized via Suzuki cross-coupling of a dibromophenylpyridine-ligated Pt(II) complex with a fluorene diboronic ester. Their optical properties are characterized by relatively strong orange room-temperature phosphorescence with well-resolved vibronic structure in both frozen 2-methyltetrahydrofuran glass and room-temperature fluid solution. Time-resolved phosphorescence spectroscopy has shown that the polymers have excited state lifetimes of approximately 14 μs. These optical properties of the oligomers and polymers are contrasted with those of small model complexes, the optical properties of which have a strong dependence on the identity of the β-diketonate ligand used. The potential utility of phosphorescent conjugated polymers is illustrated by examination of the diffusive quenching due to oxygen as a function of molecular structure.