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New strategies for the formation of two-dimensional covalent organic frameworks (2D-COFs) on surfaces.

Periodic Reporting for period 1 - CustomCOF (New strategies for the formation of two-dimensional covalent organic frameworks (2D-COFs) on surfaces.)

Reporting period: 2017-10-01 to 2019-09-30

One-dimensional polymers retain today major societal and industrial relevance (around 300 megatons are produced every year). Two-dimensional polymers, and among them two-dimensional covalent organic frameworks (2D-COFs), are one-molecule thick sheets of a crystalline and robust material endowed of a periodic array of nanopores. By tuning the building-blocks, a wide set of potential applications, ranging from superthin membranes to advanced electronics, open up. Because of this attractive perspective, such functional materials are broadly investigated today. Unfortunately, their synthetic processes are still far from performing as well as for standard polymers.
CustomCOF deals with the use of surfaces to template the formation of extended networks of such sophisticated 2D organic materials. Scanning Probe Microscopy techniques are used to study in situ reaction products to understand the polymerization process better. New synthetic approaches are explored to achieve the next generation of this type of materials, and to conceive customized versions of 2D covalent organic frameworks with a well-defined size, shape and functionality.
General protocols for the direct synthesis of 2D-COFs based on two main types of reversible chemistry, which were already reported in the literature, were first addressed in order to improve their yield and reproducibility, also on other building-blocks. The focus was also put on making our approach simple and compatible with additional experiments or techniques, for the sake of better characterization of the materials produced. CustomCOF succeeded at developing a novel an d more efficient protocol for the on-surface synthesis of 2D-COFs.
In a second phase of the project, we went one step beyond in complexity and attempted to reach additional control over the process and final product by splitting the polymerization reaction in two distinct steps. This task proved to be very challenging. We could however collect important data and information, which will be extremely useful in the future to design a new strategy to fulfill the goal of separating the process in individual well-controlled steps.
Next, CustomCOF successfully addressed the functionalization of the previously synthesized 2D materials and produced more robust versions of them.
Finally, most of our efforts were invested in controlling the polymerization degree and morphology of the developed materials. For the first time, state-of-the-art nanomanipulation techniques were applied to COF materials. Two different strategies were investigated. The first one attempted to obtain customized 2D-COFs using scanning tunneling microscopy lithography. In the second one, the supports used to template the synthesis of 2D-COFs are previously modified. We were very excited to see that we were successful in producing well-defined 2D-oligomers. Research is still ongoing and targets the fully characterization of these materials, including applications.
Great progress has been made so far. A reliable method for the on-surface synthesis of two-dimensional covalent organic frameworks that is simple, reproducible and works at room temperature and under ambient conditions has been optimized. Novel 2D-COF systems have been prepared. Considerable progress has been made in controlling the on-surface polymerization reaction. It is expected to achieve additional progress regarding 2D-COF synthesis under nanoconfinement. Further efforts will be dedicated towards controlling the synthetic progress (self-assembly strategy), and final product (different surfaces, size, shape, dispersity). Also, we will work on new post-modification strategies.
The development of graphene-like materials is still at its early stages and additional basic research is required. CustomCOF has however substantially helped in reaching a better understanding over the polymerization process of these systems. This knowledge is key for improving the processes and the quality of the products. CustomCOF has also helped bringing closer together COF on-surface and bulk research (much more advanced at this time).
Strategy followed towards reaching higher control of the imine-based sCOF product