Phosphorescence of pi-conjugated oligomers and polymers

We observed phosphorescence from a ladder-type poly-(para-phenylene) and an analogous oligomer containing five phenylene rings. The spectra are similar to the intrinsic fluorescence spectra and bear out a singlet-triplet splitting of 5000 cm(-1) (polymer) and 6800 cm(-1) (oligomer). Phosphorescence decay of the polymer occurs on a 10-100-micros scale obeying a power law and suggestive of nonradiative quenching, while that of the oligomer is asymptotically exponential with an intrinsic decay time of approximately 250 ms. The polymer also exhibits delayed fluorescence. It originates from delayed recombination of geminate electron-hole pairs rather than from triplet-triplet annihilation.