Unusual behaviours of photoluminescence by long-term illumination in alkoxy-substituted phenylene vinylene polymer

We have studied photo-induced effects of photoluminescence (PL) for dialkoxy phenylene vinylene polymer (P(MHPV)) films with different thickness under irradiation of 488 nm laser line. The samples show photo-induced PL enhancement or quenching depending on excitation level, temperature, and sample thickness. Increasing behaviour of PL intensity with exposure time is observed in relatively thicker samples and the rising rate of the PL intensity is larger under higher intensity of the excitation light. The increasing behaviour of PL intensity with exposure time is changed into the decreasing one at temperatures ≤200 K. It is proposed that these unusual behaviours are attributed to the chemical structural variation through degradation of the bridge double bonds linking the phenyl rings, resulting in partial disconnection of conjugation in the polymers during illumination and to the spatial diffusion of excited carriers to non-degraded P(MHPV) regions by energy transfer.