The triplet photoexcited states of the pentamer 2,5-di-n-octyloxy-1,4-bis ͑4',4''-bisstyryl͒styrylbenzene in a polystyrene matrix have been investigated by optically detected magnetic resonance ͑ODMR͒ spectroscopy in spin coated films at different concentrations of the blend. As previously reported for related para-phenylene vinylene ͑PPV͒ polymers, a part of the singlet excitons-the primary photoexcitations-are dissociating by intermolecular charge transfer, which results in Coulomb bound pairs of charge carriers, the distant polaron pairs ͑PPs͒. At low temperature and weak photo-excitation, however, the triplet exciton ͑TE͒ ODMR spectrum is dominant relative to that of the PPs, which points to a more efficient formation of the long living TEs than in PPV polymers. From a detailed analysis of the TE spectrum a rhombic (Dϭ0, Eϭ0.037 cm Ϫ1 ) zero-field splitting interaction could be determined. Under optical excitation a much faster saturation of TE compared to PP spectra is found, in qualitative agreement with the previously proposed triplet-triplet annihilation mechanism for ODMR. A quantitative analysis shows a stronger than expected intensity dependence at higher excitation levels, which is attributed to an increasing probability for triplet-triplet annihilation as a result of the decreasing average distance between pairs of triplet excitons. Furthermore, the PP signal shows a much faster response than that of the TEs (ϭ0.22 and 1.2 ms, respectively, measured at 2.5 K͒, which also calls for a refinement of the description of the processes involved. TE and PP signals also show markedly different behaviors under a variation of the oligomer concentration in the polystyrene matrix, and of the measuring temperature. These results are discussed in light of the different formation and recombination mechanisms of excitons and polarons in conjugated organic materials.