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H. Moura, H. Peterlik, M. M. Unterlass:
"The Conundrum of Organic Dye-Silica Hybrids: How Can Neutrons and Synchrotron Radiation Techniques Assist Us";
Talk: 11th European NESY Winterschool & Symposium on Neutron and Synchrotron Radiation, Altaussee; 2019-03-04 - 2019-03-08.

Perylene-diimide dyes (Fig. 1a) are widely used as pigments, fluorescent sensors, and n-type semiconductors in organic electronic because of their high photostability, interesting optical and electronic properties.1,2 A few supramolecular architectures of conjugated dyes with unique optical properties have been reported in the literature.3,4 In the present contribution, we report the preparation of silica nanoparticles (Fig. 1b) by incorporating rylene-dyes inside the silica matrix (Fig. 1c) using one-pot and one-step hydrothermal synthesis (HTS). HTS is a classical inorganic method used to generate various inorganic compounds such as gems and zeolites, that is environmentally friendly. Recently5,6 we showed that organic high-performance dyes can also be prepared by HTS. However, the simultaneous synthesis of both components, organic dye and inorganic SiO₂, remains unexplored. Since both components require the same hydrothermal regime for their synthesis, the preparation of supramolecular structures like dye@SiO₂ is feasible. Preliminary data suggests that the dye@SiO₂ hybrids obtained by one-pot HTS consist of silica nanoparticles, which form perylene rich regions assembled together with layered silica regions (Fig. 1c).

Here, we address important questions about the construction of the dye@silica: (i) the aggregation and/or segregation of rylene molecules inside and outside the silica nanoparticles, (ii) chemical and electronic interactions between the rylene molecules and (iii) growth of the SiO₂ nanoparticles and organization of the organic moieties inside the inorganic SiO₂ lattice. Such control on arrangement and distribution of the molecules inside the silica lattice is expected to show interesting optical properties. Neutrons and synchrotron radiation are unique probes for the characterization of structures in materials, including e.g. the atomic structure, density and size distribution of pores/galleries, roughness and correlation of internal and external interfaces of dye@SiO₂ hybrid materials. Structure and morphology of the hybrid materials here exploited have been characterized using a range of techniques such as electron microscopy, spectroscopic measurements and thermal analysis. However, more information regarding the structures´ formation need to be exploited. To date, the hydrothermal crystallization of an organic or organic-inorganic hybrid material have not been studied in real time. In-situ studies of hydrothermal crystallization via neutron diffraction (ND), for example, would be an excellent technique to identify (i) the rates of consumption of starting compounds and appearance of products, (ii) the course of crystallization in terms of crystallization rates, (iii) crystalline intermediates and (iv) give insights on the mechanistic hypotheses of crystallization of organic and inorganic crystalline phases during hydrothermal synthesis of the dye@SiO₂ hybrid materials. Such measurements have been performed by O´Hare et. al.7 to study the hydrothermal zeolite formation at the Rutherford Appleton Laboratory (UK), and it can indeed be expanded to the detailed understanding of HTS mechanisms of dye@SiO₂ hybrids preparation.

https://nesy.unileoben.ac.at/de/6430/