Non‐volatile solid‐state memory cells based on composites of metal nanoparticles and polymers are embedded in organic semiconducting host materials. This paper presents data from a wide range of materials and device structures and shows that the switching phenomenon is commonly observed.
A new procedure is described for surface grafting polymer brushes by step-growth polymerization from initiator-embedded polymeric thin films and micron- and nanometer-scale patterns. An imprint lithographic process, nanocontact molding, was used to prepare thin patterned cross-linked polyacrylate network films on silicon wafers that incorporated 4-bromostyrene in the networks. These networks present reactive 4-bromophenyl functionality at the surface that act as attachment sites for the subsequent Ni(0)- mediated step-growth condensation polymerization of 2,7-dibromo-9,9-dihexylfluorene The step-growth polymerization medium consisted of 2,7-dibromo-9,9-dihexylfluorene, Ni(0)-catalyst, and bipyridine in a toluene/dimethylformamide solvent mixture. The resulting growth of polydihexylfluorene brushes from the patterned surface was monitored by contact angle, optical spectrometry, surface profilometry and AFM. Brush growth was conducted from patterned features ranging from 100 microm to 100 nm in width and 50 nm in height. The optical and fluorescence behavior of the polyfluorene brushes was similar to that of thin polyfluorene films made by spin coating.
The synthesis of new polymers, poly(biphenylmethylene)s, derived from bistriflates of bisphenol-type monomers, by Ni(0)-mediated polymerization has been presented. These polymers are interesting because of the nature of the polymer backbone that contains biphenyl units separated by substituted methylene units. The solubility, mechanical properties, and electrical properties of the polymers can be altered by proper selection of the methylene substituents. Polymers and oligomers had molecular weights ranging from 2000 to 15 000 g/mol, as measured by calibrated gel permeation chromatography (GPC), though light scattering and MALDI studies indicate that GPC tends to underestimate the molecular weights of these polymers. The polymers have T g's between 230 and 300 °C and have thermal stabilities ranging from 400 to 493 °C. Thermally cross-linkable, 4-phenylethenyl end-capped oligomers were synthesized and fabricated into thin-film electronic devices, and preliminary results on their characterization are discussed. The unique structure of the polymer backbone makes these materials potentially interesting in electrical applications where large-band-gap polymers with good electron/hole mobility and good thermal and oxidative stability are required.
The photophysical properties of several acceptor substituted 1-arylpyrene derivatives were investigated. The fluorescence spectra strongly depend on the nature of the aryl moiety and the position and number of methoxycarbonyl acceptor groups. Dual fluorescence, originating from a locally excited and a charge transfer state, was observed for the diester derivatives. The solvent dependence of the dual fluorescence and the slightly curved solvatochromic plots indicate a change of the character of the excited states from solvents of low to high polarity. The rate constants for fluorescence and nonradiative decay were calculated to reveal the nature of the excited-state relaxation, that is, the increase of the mesomeric interactions by geometrical flattening or stabilization of the CT state by further twisting toward perpendicularity. Flattening is the major relaxation pathway of the diester phenylpyrene derivative in nonpolar solvents whereas in highly polar solvents the low value for the fluorescence transition dipole moment (M f ) indicates stabilization of the charge transfer state by further twisting. The fluorescence of the diester biphenylpyrene derivative originates from a locally excited state (LE) in nonpolar solvents. The low value for M f in polar solvents and the change of the relative intensity of the dual fluorescence signals with the temperature indicate that the red-shifted fluorescence can be assigned to a twisted intramolecular charge transfer state.
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