In-situ luminescence analysis of coordination sensors: looking inside chemical reactions

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Many modern technologies depend on the discovery of materials with new or improved properties, which are usually solid compounds. Although a very large number of effective methods are available today, almost all synthesis approaches have a basic principle in common, in which certain reactants are brought to react and, only in the end of the reaction, the often randomly formed products are characterized. For developing strategies for a rational synthesis of solids or for discovering new compounds, processes such as nucleation, crystal growth or formation of intermediates must be examined in detail during the reactions. Because these intermediates can rapidly convert to other phases, conventional ex-situ methods are not suitable. Therefore, many very efficient methods such as X-ray diffraction, nuclear magnetic resonance and infrared spectroscopy have been used for in-situ monitoring of chemical reactions in the past few years. However, besides many advantages, these methods have also grave disadvantages as for instance with regard to the detection limit, temporal resolution or type of substances to be investigated. One method that could provide additional information as well as overcome the above mentioned disadvantages of the available characterization methods, is the luminescence analysis of coordination sensors applying high-resolution CCD detectors, which has not yet been used for the in-situ monitoring of chemical reactions so far. Within this approach, emitting coordination sensors as the lanthanide ions Eu3+, Eu2+, Ce3+ are introduced into the system under examination and monitored with the aid of in-situ luminescence under real reaction conditions (in-situ Luminescence Analysis of Coordination sensor - ILACS). Since the luminescence of these ions are highly dependent on the coordination environment, this method provides information about the changes in the coordination number, bond lengths, covalence of the ligands and symmetry of the cation site during chemical reactions. This procedure is easily available, is characterized by high sensitivity and high temporal resolution and can also be used for studying very small crystallites or amorphous materials. Hence, the aim of the here proposed project is to develop a new in-situ characterization method and to test its performance for different model systems. For assembling the in-situ luminescence measurement setup, first the highly luminescent [Eu(1,10-phenanthroline)2(NO3)3] complex shall be applied. Then, more complex systems such as the conversion of different phases of calcium phosphate and carbonate as well as the elucidation of open questions concerning the formation of amorphous phases before the start of their crystallization shall be examined. In this context, it shall be also analyzed whether the formation of other alkaline earth metal compounds such as SrCO3, BaCO3 and SrHPO4 also take place over amorphous intermediates.