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

Abstract

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.

Optical Properties of Hybrid Organic‐Inorganic Materials and their Applications

“…The first examples of the use of hybrid materials in lighting (more specifically in solid-state lighting, SSL) appeared in 2001 with layered crystalline organic-inorganic perovskites. [8] Although the interest on these hybrid perovskites as single-phase white light emitters continue, [9,10] the wide range of materials with potential application in SSL would include dye-bridged, [11][12][13][14][15][16][17] dyedoped [18] and quantum dots-doped [19] siloxane-based organicinorganic hybrids, and metal organic frameworks. [20] Despite the interest of organic-inorganic hybrid perovskites in lighting, the most exciting application of these materials is in solar cells.…”

“…[59][60][61] The first examples of white LEDs (WLEDs) based in hybrids date back to the final of last century comprising dye-modified silanes incorporating hole-or electron-transporting units and light-emitting species in the orange [62] and green [11] spectral regions. Later on, more efficient WLEDs were reported involving silsesquioxane hybrid matrices, as, for example, that based on the phenylenevinylenediimide precursor, luminance value of 10 cd·m −2 for voltages lower than 30 V, [12] and that based on polyhedral oligomeric silsesquioxanes bearing in the structure a dye molecule from the cyanine family, threshold operating voltage of 4 V. [63] An intriguing example is the fabrication of a WLEDs by coating a commercial UV LED (390 nm) with a periodic mesoporous organosilica (PMO) film doped with Rhodamine 6G (Rh6G) and synthesized by surfactant-templated sol-gel polycondensation using a 1,3,6,8-tetraphenylpyrene (TPPy)-containing organosilane precursor. [13] The blue emission of the films, emission quantum yield of 0.70, overlaps the Figure 3.…”

Tuning and Transcription of the Supramolecular Organization of a Fluorescent Silsesquioxane Precursor into Silica‐Based Materials through Direct Photochemical Hydrolysis–Polycondensation and Micropatterning

“…It contrasts with the morphology of the film obtained by spin-coating of the related precursor without the cyclohexyl groups. [10] It was extremely heterogeneous with R rms ¼ 40 nm (Fig. 1).…”

“…In a related approach, using the triethoxysilane function as sterically hindered fragment, we were able to synthesize a highly fluorescent and electroluminescent compound. [10] After sol-gel hydrolysis, a change in the aggregation behavior of the chromophore from J-type to H-type occurred. The resulting material exhibited no more fluorescence but higher photoconductivity.…”

Organic Light-Emitting Diodes Based on Phthalimide Derivatives: Improvement of the Electroluminescence Properties

“…Among emitters, phthalimide-based materials are an attractive class of materials by their good electron-transport abilities [13,14] and their remarkable electron-accepting ability [15,16]. When combined with the oligophenylenevinylene core, materials with a wide bandgap can be designed, the phthalimide part conferring the electron-transport properties lacking to the oligophenylene central core [17]. To date, this family of fluorescent materials has only been scarcely investigated in the literature.…”