The absorptive and emissive behavior of four highly fluorescent bisalkyl-substituted poly(p-phenyleneethynylenes) (R = hexyl, dodecyl, 2-(ethyl)hexyl, and 3,5,5-trimethylhexyl) was examined. Aggregate and excimer formation was seen in solution and in the solid state by a combination of absorption and fluorescence spectroscopy in solvent/nonsolvent (chloroform/methanol) mixtures and in thin films. The aggregates were identified by the occurrence of a sharp absorption centered at 440 nm, undetectable in dilute chloroform solution, and a broad emission at 504 nm. The average size of the aggregate formed in chloroform/methanol solvent mixtures must exceed 1.5 μm, as was evidenced in filtering-experiments utilizing a set of membranes with different pore sizes to successively remove smaller aggregates.

SUMMARY: The solvent and temperature dependent aggregation of high molecular weight bis[S-(+)-3,7-dimethyloctyl)] substituted poly(p-phenyleneethynylene) (PPE, 2) was examined by absorption, emission and circular dichroism spectroscopy. All herein employed methods strongly support the view that 2 forms ordered aggregates in the solid state and in solvent mixtures. This is the first case in which a chiral high molecular weight PPE displays its aggregation by both optical and chiroptical methods.

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Acetoacetanilide and substituted acetoacetanilides were trilithiated in excess lithium diisopropylamide, and the polylithiated intermediates were regioselectively condensed with lithiated methyl thiosalicylate, followed by acid cyclization to afford substituted N-aryl-4-oxo-4H-1-benzothiopyran-2-acetamides (thiochromone-2-acetamides).Résumé : On a effectué une trilithiation de l'acétoacétanilide et d'acétoacétanilides substitués en procédant dans un excès de diisopropylamidure de lithium, et les intermédiaires polylithiés ont subi une condensation régiosélective par réaction avec du thiosalicylate de méthyle lithié, suivie d'une cyclisation acide conduisant à des N-aryl-4-oxo-4H-1-benzothiopyran-2-acétamides (thiochromon-2-acétamides).Mots clés : thiochromones; synthèse, base forte anion multiple; condensation du type de Claisen.