Self-assembled Monolayers of Alkylammonium Ions on Mica: Direct Determination of the Orientation of the Alkyl Chains

Near edge X-ray absorption fine structure spectroscopy was used to study the orientation of the alkyl chains in monolayers of (R3RN+)-R-1-N-2 and (R2R2N+)-R-1-N-2 (R-1 = methyl and R-2 = octadecyl), self-assembled on muscovite mica via ion exchange. The alkyl chains adopt a random orientation in the monooctadecylammonium ions. Dimethyldioctadecylammonium ions, however, form a well-ordered self-assembled monolayer, The average tilt angle between the alkyl chains and the surface normal is 38 degrees, The difference between the mono- and the dioctadecylammonium ions reflects at least partially the packing density of the alkyl chains. When adsorbed on muscovite mica, dimethyldioctadecylammonium ions establish monolayers that are similarly well ordered as alkanethiol monolayers on gold. (C) 1999 Academic Press.</p

Homoconjugation in poly(phenylene methylene)s: A case study of non-π-conjugated polymers with unexpected fluorescent properties

Poly(phenylene methylene) (PPM) exhibits pronounced blue fluorescence in solutions as well as in the solid state despite its non-π-conjugated nature. Optical spectroscopy was used to explore the characteristics and the physical origin of its unexpected optical properties, namely absorption in the 350–450 nm and photoluminescence in the 400–600 nm spectral regions. It is shown that PPM possesses two discrete optically active species, and a relatively long photoluminescence lifetime (&gt;8 ns) in the solid-state. Given the evidence reported herein, π-stacking and aggregation/crystallization, as well as the formation of anthracene-related impurities, are excluded as the probable origins of the optical properties. Instead there is sufficient evidence that PPM supports homoconjugation, that is: π-orbital overlap across adjacent repeat units enabled by particular chain conformation(s), which is confirmed by DFT calculations. Furthermore, poly(2-methylphenylene methylene) and poly(2,4,6-trimethylphenylene methylene) – two derivatives of PPM – were synthesized and found to exhibit comparable spectroscopic properties, confirming the generality of the findings reported for PPM. Cyclic voltammetry measurements revealed the HOMO–LUMO gap to be 3.2–3.3 eV for all three polymers. This study illustrates a new approach to the design of light-emitting polymers possessing hitherto unknown optical properties

Vermeidung von Abfaellen durch abfallarme Produktionsverfahren Kunststoffteilelackierung

SIGLEAvailable from TIB Hannover: F98B2083 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekUmweltministerium des Landes Baden-Wuerttemberg, Stuttgart (Germany)DEGerman