Showing papers by "Mark S. Wrighton published in 1996"

Efficient Solid-State Photoluminescence in New Poly(2,5-dialkoxy-p-phenyleneethynylene)s

Abstract: A series of novel poly(2,5-dialkoxy-p-phenyleneethynylene)s (PPEs) has been prepared by the palladium-catalyzed cross-coupling polycondensaton of aryl acetylenes and aryl iodides. Different alkoxy side chains including n-hexadecyloxy, n-octyloxy, (2-ethylhexyl)oxy, (2-methylpropyl)oxy, (3-(dimethylamino)propyl)oxy, and (7-carboxyheptyl)oxy groups were attached to the rigid-rod polymer main chain. With this structural concept, polymers having an identical conjugated backbone but different supramolecular structures in the solid state could be achieved. X-ray diffraction measurements on thin films show that the polymers which have sterically hindered side chains are essentially disordered, while those with only linear side chains can form lamellar structures with significant degrees of long-range order. High photoluminescence (PL) quantum yields, up to 0.86 in solution and 0.36 in the solid state, have been measured for the new materials. While the solution quantum yields are independent of the functionaliza...

Layer-by-Layer Growth of Electrostatically Assembled Multilayer Porphyrin Films

Abstract: The feasibility of preparing multilayer porphyrin films with monolayer control of composition and thickness is demonstrated. Successive dip-coating of tetraruthenated zinc porphyrin, [ZnTPyPBpy]4+, and meso-tetraphenylporphyrin sulfonate, [M-TPPS]4-, is shown to result in linear growth of the film thickness (12.7(6) A/bilayer) and optical absorbance as a function of the number of bilayers. These results strongly suggest a layer-by-layer assembly of compositionally homogeneous films of up to 30 bilayers. The assembled multilayer composite films have been characterized by UV−vis spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and electrochemical methods. Electrodes modified with these films exhibit a reversible wave at 0.94 V and are photocatalytically active toward the reduction of O2. Our findings suggest that the layer-by-layer growth method may be a general route to compositionally modulated porphyrin films of arbitrary thickness and rationally tail...

Controlling the Adhesion of Conducting Polymer Films with Patterned Self-Assembled Monolayers

Abstract: A photosensitive self-assembled monolayer (SAM) is selectively irradiated to fabricate a pattern on an Au electrode, and a thin film of aniline or 3-methylthiophene is deposited on it by electropol...

Effect of the solid state structure on the third-order nonlinear optical response of poly(2,5-dialkoxy-p-phenyleneethynylene)s

Abstract: The third-order nonlinear optical (NLO) properties of a series of poly(2,5-dialkoxy-p-phenyleneethynylene)s (PPEs) have been investigated in solution and in the solid state. In these PPEs, different alkoxy side chains are attached to the rigid-rod polymer main chain, leading to a series of polymers having an identical conjugated backbone but different supramolecular structures in the solid state. The nonresonant third-order NLO susceptibilities χ(3)(−3ω;ω,ω,ω) were measured by third-harmonic generation experiments. χ(3) values of up to 7.5 x 10-20 m2/V2 in solution and 14 × 10-20 m2/V2 in the solid state were determined. In solution, the NLO susceptibilities were found to be proportional to the content of polymer backbone, which depends on the functionalization of the PPEs. The solid state NLO susceptibilities were found to be related to the degree of long-range order in the samples, increasing with increasing order. In samples which adopt only a small extent of long-range order, the rigid-rod conjugated ...