We report on the transient and steady-state optical responses of the chromophore 2,2′-bithiophene-5,5′-diylbis(phosphonic acid) (BDP) incorporated within a single zirconium-phosphonate layer as a function of chromophore density. While the dilute solution optical response of BDP reveals no anomalous behavior, its characteristics are substantially different when confined within a monolayer. We vary the concentrations of layer constituents to determine the extent of interaction between BDP moieties within a single monolayer. We observe limited initial aggregation of BDP, the extent of which is determined largely by the conditions under which the monolayer is formed. Over time, the fractional contribution of BDP aggregates to the total optical response decreases to a limiting value, implicating surface adsorption site density as the dominant factor in determining the morphology of the organobis(phosphonate) layer. Motional relaxation measurements of BDP within the layer show that the chromophores are immobile on the hundreds-of-picoseconds time scale of our experiments.

We report on the lifetime and motional dynamics of Zirconium Phosphonate (ZP) monolayers containing oligothiophene chromophores in a range of concentrations. Monolayers were formed on fused silica substrates and on a 15 Å oxide layer formed on crystalline Si(100) substrates. For both interfaces, the fluorescence lifetime behavior of the chromophores 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 ∼35° with respect to the surface normal. For monolayers formed on silica, 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 primed silicon substrate allows for greater motional freedom of the chromophores 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).

A homologous series of novel amorphous oligothienyl-triphenylamines, comprised of head-to-tail coupled oligo(3-hexylthiophene)s covalently linked to a triphenylamine core, are disclosed. These hybrid systems, which differ by the length of the oligothiophene units from a monothiophene up to a quaterthiophene, were created via palladium-catalyzed cross-coupling reactions in good yields. The optical and electrochemical properties of these compounds were thoroughly investigated and are compared to the corresponding parent linear non-functionalized oligothiophenes, clearly demonstrating that these newly synthesized hybrid systems are characterized by outstanding absorption and emission properties. These molecules exhibit fluorescence quantum yields as high as 65%, which is unexpectedly high for thiophenebased materials. Based on this available data set, structure-property relationships were established, providing a deeper insight into the electronic nature of these materials and in this respect elucidating electronic differences between these star-shaped structures and their corresponding parent linear oligothiophenes.