TEMPERATURE-DEPENDENCE OF THE PHOTOBLEACHING PROCESS OF FLUORESCEIN IN POLY(VINYL ALCOHOL)

The fluorescence spectrum of fluorescein dissolved in poly(vinyl alcoh ol) (PVA) was recorded at various temperatures. These fluorescence spe ctra indicate that there is an enhancement of the photobleaching proce ss of the dye at T>350 K. This temperature corresponds to the glassy t ransition of PVA which involves rupture of hydrogen bonds. The rupture of these bonds has also been followed by near-IR spectroscopy. The co incidence between these temperatures suggests that the glass transitio n and the enhancement of the photobleaching process are correlated, an d that the former is strongly dependent on the mobility of the polymer chains. The determination of this limit temperature is important for technological applications of the PVA-fluorescein system.