No abstract

Syntheses of complex molecular mixtures on the preparative scale are often challenging steps for chemists, which go hand in hand with expensive purification steps. Herein, the preparation and isolation of unsymmetrically substituted porphyrins, obtained from statistical reactions between two benzaldehydes, were investigated. Therefore, a semi-automated modular process was developed to lower the consumable costs, save time, and reduce waste production. We utilized a monomode microwave reactor equipped with an autosampler, and a medium pressure liquid chromatography (MPLC) flash purification device, equipped with a UV/Vis detector and a re-usable glass column packed with SiO 2. With this method, it was possible to synthesize and purify several statistical porphyrin mixtures, while simultaneously reducing the environmental factor (Efactor) significantly, compared to conventionally performed porphyrin syntheses. Our approach shows that a sustainable investigation of academically relevant low-symmetrical porphyrins can be carried out feasibly, without sacrificing invested time.

Understanding the adsorption of organic molecules on surfaces is of essential importance for many applications. Adsorption energies are typically measured using temperature-programmed desorption. However, for large organic molecules, often only desorption of the multilayers is possible, while the bottom monolayer in direct contact to the surface cannot be desorbed without decomposition. Nevertheless, the adsorption energies of these directly adsorbed molecules are the ones of the most interest. We use a layerexchange process investigated with X-ray photoelectron spectroscopy to compare the relative adsorption energies of several metalated tetraphenylporphyrins on rutile TiO 2 (110) 1 × 1. We deposit a mixture of two different molecules, one on top of the other, and slowly anneal above their multilayer desorption temperature. During the slow heating, the molecules begin to diffuse between the layers and the molecules with the stronger interaction with the surface displace the weaker-interacting molecules from the surface and push them into the multilayer. The multilayers eventually desorb, leaving behind a monolayer of strongly interacting molecules. From the ratio of the two different porphyrin molecules in the residual monolayer and the desorbed multilayer, we can calculate the equilibrium constant of the layer-exchange process and thereby the difference in adsorption energy between the two different porphyrin molecules.

The Front Cover shows a laboratory bench, with instruments, equipment, and a chalkboard. Is there a way to implement the philosophy of “reduce, reuse and recycle” in academic research? The recycle sign underlines the rising awareness for this topic, which is steadily gaining in importance. Especially in porphyrin sciences, using semi‐automated flash chromatography can decrease significantly the cost of consumables, such as chlorinated solvents and silica gel. With a re‐usable glass column for preparative separation, even the purification of statistical reaction mixtures can be managed, while reducing the waste and thus the environmental factor significantly. More information can be found in the Full Paper by Dominik Lungerich, Norbert Jux and co‐workers.

Invited for this month's cover are the groups of Dominik Lungerich at the Yonsei University (Korea) and Norbert Jux at the Friedrich‐Alexander‐University Erlangen‐Nuernberg (Germany). The cover picture shows a laboratory bench, with instruments, equipment, and a chalkboard. Here, the question arises if in academic research exists a way to implement the philosophy of “reduce, reuse and recycle”. The recycle sign underlines the rising awareness for this topic, which is steadily gaining in importance. Especially in porphyrin sciences, using semi‐automated flash chromatography can decrease significantly the cost of consumables, such as chlorinated solvents and silica gel. With a re‐usable glass column for preparative separation, even the purification of statistical reaction mixtures can be managed, while reducing the waste and thus the environmental factor significantly. Read the full text of their Full Paper at 10.1002/cmtd.202000055.