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Absorbance and fluorescence spectra of dilute solutions and thin films of polyfluorene rigid-rod polymers 1-3 bearing two hexyl, octyl, or dodecyl groups at the 9-position define the effect of polymer chain interactions on excited state relaxation. Film morphology is controlled by annealing of 250 nm thick films. Under these conditions, the degree of interchain interaction follows the degree of thermotropic liquid crystalline ordering which is, in turn, a function of the length of the attached alkyl substituents. Alkyl substituents also affect the solubility of these polymeric liquid crystals in organic solvents; low solubility favors strong ground state aggregation, as is evidenced by a red-shifted absorption band. In the annealed films, aggregate and excimer formation is evidenced by a broadening of the absorbance band, an increase in the intensity of the low energy emission, the appearance of new long-lived fluorescent species, and structure-dependent changes in observed fluorescence quantum yields.

A palladium-nanoparticle-cored G-3 dendrimer, characterized by TEM, TGA, absorption, and IR spectroscopies, has approximately 300 Pd atoms in the metallic core and an average diameter of 2.0 nm, to which are attached fourteen G-3 dendrons. Nearly 90% of the metal nanoparticle surface is unpassivated and available for catalysis. The dendrons inhibit metal agglomeration without adversely affecting chemical reactivity. Thus, preliminary investigations have shown that Pd-G-3 can efficiently catalyze Heck and Suzuki reactions.

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the organizing element which promoted complex formation was the polymer, to which pyrochlorophyll was bound by ligation and DTNB by counterion attraction. In the present case, the organizing element is evidently the cationic micelle.Chl and its relatives have been examined in almost every conceivable kind of model system in efforts to imitate photosynthesis. To our recollection, however, this is the first report of its presence in cationic inverted micelles. Chl has been reported in anionic inverted micelles of aerosol OTIS though these may have been more in the nature of microemulsions, with a clearly defined internal aqueous phase. Inverted micelles have been promoted as models of the interiors of proteins or lipoproteins, where numerous biological reactions, including the primary processes of (18) Pileni, M. P.; Lerebours, B.; Brochette, P.; Chevalier, Y. J . Photochem. An unusual photovoltaic effect has been observed in symmetrical cells consisting of indium-tin oxide (ITO) electrodes and a liquid crystal porphyrin (LCP, zinc octakis(8-octyloxyethy1)porphyrin). The illuminated electrode acts as a photoanode; the direction of current flow reverses upon reversal of the direction of illumination. Stable photocurrents of up to ca. 0.4 mA/cm2 have been measured under illumination with a 150-W Xe lamp (intensity ca. 150 mW/cm2). The photocurrentincreases linearly with incident light intensity (I,) at all wavelengths up to I, > 1OIs photons s-I cm-2. This photovoltaic effect is interpreted as resulting from exciton dissociation at the illuminated electrode leading to the preferential photoinjection of electrons into the IT0 electrode and holes into the porphyrin. This appears to be the first unambiguous example of a photovoltaic cell controlled entirely by interfacial kinetics. The predominance of the photoinjection process in these capillary-filled liquid crystal (solid-phase) films, and its relative absence in similar cells containing evaporated films of porphyrins and phthalocyanines, is attributed to the single-crystal-like character of the LCP films. The wavelength dependence of the photocurrent (action spectrum) is a function of the cell thickness, correlating with the absorption spectrum for thin cells, while it is inversely correlated for thicker cells. This is attributed to an effective cell resistance that is determined by the number and spatial distribution of carriers photogenerated in the bulk LCP. An approximate mathematical model of these two processes, photoinjection at the interface coupled with photoconductivity in the bulk LCP, is proposed which reproduces the experimental results. (20) (a) Chandrasekhar, S. Mol. Cryst. Liq. Cryst. 1981, 63, 171. (b) Destrade, C.; Tinh, N. H.; Gasparoux, H.; Malthete, J.; Levelut, A. M. Mol. Tran-Thi, T.-H.; Briois, V.; Simon, J.; Ohta, K.

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