Absorption and Fluorescence Characteristics of Pyranine Molecules Embedded in Anodic Porous Alumina

Abstract

Pyranine (trisodium 8-hydroxypyrene-1,3,6-trisulfonate) molecules were embedded in anodic porous alumina at varying pH. The UV-Vis absorption spectra of pyranine embedded in anodic porous alumina showed a peak at around 405 nm that was attributable to the protonated form of pyranine (PyOH). The amount of adsorbed pyranine, which was dependent on the aqueous dye solution pH, reached a maximum at around pH 5, indicating that the adsorption of pyranine results from electrostatic interaction between the anodic porous alumina positive surface charges and negative pyranine sulfonate groups. The fluorescence spectra had a peak at around 510 nm that was attributable to the deprotonated form of pyranine (PyO -), suggesting that the anodic porous alumina provides a water-rich environment. Before sealing, the fluorescence intensity of the material decreased during continuous excitation. However, the fluorescence remained more or less constant after sealing. These results indicate that sealing decreases the photochemical decomposition of pyranine with oxygen molecules because oxygen molecule diffusion can be suppressed. Keywords