| A novel series of polyether dendrimer segments (dendrons) end-capped with pyrenyl-, naphthyl-, or methyl groups at the chain ends has been prepared by a convergent growth method. Steady-state fluorescence measurements indicate the absence of intramolecular naphthalene excimer in the naphthyl-capped dendrons. However, in the pyrenyl-capped dendrons, excimer emission predominates. Fluorescence from both the naphthyl monomer and pyrenyl excimer are quenched when a suitable electron donor (e.g., a 3- (dimethylamino) phenoxy group) is covalently attached at the dendron focal point. No sensitized emission from the dendron backbone is observed in the chromophore-labeled dendrons, although the control methyl-capped dendron fluoresces weakly at 310 nm when excited at 284 nm. Absorption and fluorescence spectra, fluorescence quantum yields, and fluorescence lifetimes for the chromophore-labeled dendrons are reported.; Ring Opening Metathesis Polymerization (ROMP) techniques were used to polymerize a functionalized norbornene macromonomer bearing pendant naphthyl-capped dendrimer segments. The resulting polymer, with four naphthyl groups per repeat unit, has a very high concentration of fluorophores, and bears the highest dendrimer substitution yet reported for a linear polymer. The fluorescent properties of this polymer are compared to those of the corresponding dendrimer segment.; The effects of intermittent irradiation on the photoefficiencies of heterogeneous photocatalytic reactions were studied. Variation of dark recovery time influences the efficiency of a heterogeneous photocatalytic oxidation on irradiated TiO{dollar}sb2{dollar} particles suspended in non-aqueous media, but does not affect the efficiency of a parallel photocatalyzed reduction. The efficiency of the photocatalyzed oxidation of 1-octanol on Degussa P-25 TiO{dollar}sb2{dollar} in oxygenated acetonitrile nearly doubled when the dark interval between excitation pulses was increased from 0.1 s to 1 s. No improvement in photoefficiency could be detected in the photocatalytic reduction of p-nitroacetophenone under the same conditions. |
