Raman Marker Bands for In-situ Quality Control During Synthesis Of Two-Dimensional Conjugated Metal-Organic Frameworks

Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) are a subclass of MOFs that are of particular interest for electrocatalysis due to their good intrinsic conductivity. The electrochemical properties of such 2D frameworks are strongly related to their structure, which in turn is influenced by the synthesis conditions. However, even under formally identical conditions, MOF crystals with different structural properties are obtained, and to date there is no easy-to-apply method to predict the quality of MOF crystals already during synthesis. In the present work, we monitored the formation of phthalocyanine-based 2D MOFs at the air-water interface using in-situ Raman spectroscopy and identified Raman marker bands that characterise the degree of linker aggregation, the reaction progress, and the yield of MOFs formed during the reaction. Using transmission electron microscopy (TEM) measurements on the MOF crystals after synthesis, a correlation between the Raman marker bands and the resulting crystalline domain size distribution of the MOF could be derived. Thus, a method for a non-invasive, fast and simple in-situ quality assessment of the synthesised MOFs was established. These results are an important step towards the automation of MOF synthesis.