The effect of broken conjugation on the optical absorption spectra of the triplet states of isolated chains of poly(phenylene vinylene)s

The triplet states of a series of poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene]s with different conjugated fractions x (MEH-PPV-x) have been studied by pulse radiolysis with UV/VIS/NIR spectrophotometric detection. Decreasing conjugated fraction caused a blue shift of the absorption maxima, and a decrease of the extinction coefficients and oscillator strengths. The spectral properties can be explained by the distribution of conjugation lengths in the polymer chains with randomly placed conjugation truncations. Quenching of the triplet state by the ground-state polymer (self-quenching) was observed. No evidence was found for energy transfer from the triplet states of shorter to longer conjugated segments on a time-scale of microseconds.