PHOTOPHYSICAL STUDIES OF ULTRATHIN FILMS - CHARACTERIZATION OF PS ANDPMMA ON FUSED QUARTZ BY FLUORESCENCE SPECTROSCOPY OF PYRENE AND (4-(1-PYRENYL)BUTYL)TRIMETHYLAMMOMIUM BROMIDE

Ultrathin films of polystyrene (PS) and poly(methyl methacrylate) (PMM A) coated on fused quartz plates (or slides) by dip coating are examin ed by using fluorescence spectroscopy. Cations of the pyrene derivativ e (4-(1-pyrenyl)butyl)trimethylammonium bromide (PBN) are adsorbed ont o the quartz slides from aqueous solutions. The rate of dynamic quench ing and prompt quenching by O-2 of the PBN fluorescence on the slide i n the presence of PMMA and PS films at varying degrees of coverage ind icates that, at low coverage, PS films are patchy while PMMA films are continuous. These results are in agreement with published data from A FM studies of similar systems. The fluorescence of pyrene dissolved in ultrathin films on quartz and on hydrophobic (surface derivatized) qu artz slides is also examined. As revealed by the trend in pyrene III/I and average fluorescence decay time with coverage, a fraction of the pyrene molecules in PS films diffuse to the polar quartz surface, wher e they become adsorbed. PMMA, on the other hand, blocks access of pyre ne to adsorption sites on the quartz surface presumably by an interact ion between carbonyl groups and quartz surface hydroxyls. This fluores cence technique thus provides additional information to AFM in the pen etration of reactive species, such as O-2, to the silica-polymer inter face and in the polymer-mediated interaction of molecular dopants, suc h as pyrene, with the silica surface.