Nanostructuration of Phenylenevinylenediimide-Bridged Silsesquioxane:From Electroluminescent Molecular J-Aggregates to Photoresponsive Polymeric H-Aggregates

摘要

A new approach to control molecular aggregation of pi-conjugated chromophores in the solid state has been investigated.Our strategy was to use a modifiable bulky fragment which should induce a J-aggregation and offer the possibility to reach an H-aggregation upon its chemical modification by lateral slip of pi-conjugated molecules.The chosen fragment for that purpose was the hydrolyzable triethoxysilane function (Si(OEt)_3).Our objective was to design and synthesize electroluminescent or solar cell hybrid organic-inorganic materials by the sol-gel process applied to a bifunctionalized silane.With this intention,the synthesis of the sol-gel processable phenylenevinylenediimide Silsesquioxane 6 was accomplished and the study of spin-coated thin films of the pure silane precursor subjected or not to the sol-gel process has been carried out.Optical properties of 6 are consistent with the formation of J-aggregates in the solid state due to the steric hindrance introduced by the triethoxysilane units.Conversely,the spectroscopic behavior observed for the hybrid film 6F is attributed to an H-aggregation corresponding to a "card pack" orientation of the distyrylbenzeneimide chromophores in the compressed silicate network.Morevover,6 and 6F also exhibited different electronic behaviors:light-emitting diodes exhibited high brightness with the native precursor 6 and almost no light output with the sol-gel processed Silsesquioxane 6F.Photovoltaic cells showed the opposite behavior with low photocurrent generation in the precursor case and higher photocurrents with the sol-gel processed layers.These results provide a deeper understanding of the present self-assembly process that is strongly governed by the molecular packing of the oligosiloxane precursor.