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

The fluorescence spectrum of fluorescein dissolved in poly(vinyl alcohol) (PVA) was recorded at various temperatures. These fluorescence spectra indicate that there is an enhancement of the photobleaching process of the dye at T>350 K. This temperature corresponds to the glassy transition of PVA which involves rupture of hydrogen bonds. The rupture of these bonds has also been followed by near-IR spectroscopy. The coincidence between these temperatures suggests that the glass transition and the enhancement of the photobleaching process are correlated, and 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.