THE ROLE OF SUBSTRATE IDENTITY IN DETERMINING MONOLAYER MOTIONAL RELAXATION DYNAMICS

We report on the lifetime-and motional dynamics of Zirconium Phosphona te (ZP) monolayers containing oligothiophene chromophores in a range o f concentrations. Monolayers were formed on fused silica substrates an d on a 15 Angstrom oxide layer formed on crystalline Si(100) substrate s. For both interfaces, the fluorescence lifetime behavior of the chro mophores is identical and does not depend on chromophore concentration within the monolayer. Transient anisotropy measurements reveal that, for both substrates, the chromophores are oriented at similar to 35 de grees with-respect to the surface normal. For monolayers formed on sil ica, there is no evidence for chromophore motion, while motion is seen for monolayers formed on silicon. Despite the substantial similarity between the two families of monolayers, the surface roughness of the p rimed silicon substrate allows for greater motional freedom of the chr omophores in the monolayers. We discuss these findings in the-context of the differences in substrate surface roughness and domain sizes as measured by atomic force microscopy (AFM).