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Advanced optoelectronic materials through dynamic combinatorial assembly

Final Report Summary - OPTOELECTRONIC_DCA (Advanced optoelectronic materials through dynamic combinatorial assembly)

The aim of the project was to construct new materials for solar cells and other electronic devices starting from relatively small molecular components, using a concept called 'dynamic covalent chemistry'. In this concept, small molecular components are put together to form larger structures through the formation of a reversible covalent bond. Because the chemistry of this bond formation is reversible, the system can optimise its own structure, possibly leading to highly ordered materials, a prerequisite for efficient electronic devices such as solar cells.

The work was divided along the following lines:

1) synthesis of conjugated molecules for dynamic covalent assembly, and study of their self assembly and optoelectronic properties;
2) investigation of dynamic bond formation in organic materials;
3) investigation of multicomponent self-assembly.

The first line was the original objective of the project. Because it was found out in the course of the project that an adequate fundamental understanding of the principles behind dynamic covalent assembly of functional materials was missing, an investigation into these fundamentals was launched, leading to lines 2 and 3.

The main results of the project:

1) Potentially conducting, optically active (coloured) molecules were synthesised, and their self-assembly and optoelectronic properties were investigated. For a particular type, an anthracene-derived system, conduction measurements were performed in collabouration with the Optoelectronic Materials group and Molecular Electronic Devices group at TU Delft. With an oligothiophene based system, dynamic covalent polymers were constructed, that can form spontaneously in water upon mixing of the monomers. The lengthening of the pi-system results in a large optical response. Resulting from the reversible nature of the dynamic covalent bond, these polymers are highly responsive to changes in their environment (Angew. Chem., in preparation; J. Am. Chem. Soc., in preparation).

2) Using simple surfactant precursor molecules equipped with amine, aldehyde and hydrazide functional groups, dynamic covalent bonds were found to be stabilised to a great extent in supramolecular aggregates (Angew. Chem., 2011). The use of catalysts was found to have a drastic effect on the morphologies of supramolecular materials built up of dynamic covalent bonds, even though the catalysis did not change their composition. Here, catalysis provides access to non-equilibrium metastable material states with drastically different mechanical properties and appearance (Nature Chem., submitted).

3) First attempts were made at controlling multicomponent self assembly, both in dynamic covalent materials and in supramolecular materials. In the latter, we achieved the use of molecular chaperones to steer the self-assembly pathways of multisegment assemblers (Angew., 2011). The dynamic covalent system was found to be able to self-select its own best-fitting components from a mixture of starting materials (PNAS, in preparation).

The development of a range of new concepts and methodologies in dynamic covalent chemistry and assembly will likely have a profound impact on science and possibly society. The use of catalysis in the construction of new soft materials with controllable mechanical properties will likely be applied in creating new matrices for stem cell differentiation and will thus contribute to the current health challenges faced by society. Component selection in dynamic covalent surfactant assemblies sheds light on the origins of life on earth, as it shows how the first membranes and compartments have likely come about.