SUSTAINABLE SYNTHETIC METHODOLOGIES FOR THE PREPARATION OF ORGANIC SEMICONDUCTING MATERIALS: ORGANIC (OPTO)ELECTRONICS GROWING “GREEN”

The worldwide demand for energy-efficient and high-performing (opto)electronics, along with the increasing need for economically feasible and environmentally friendly chemistry, both require semiconducting materials that are both scalable and sustainable. The concern with waste generation and toxic/hazardous chemicals usage has already moulded many operations in chemical and manufacturing industries. To date, common syntheses to access organic semiconductors require the use of large quantities of toxic and/or flammable organic solvents, often involving reagents and by-products that are harmful to health and environment. Research in the field of organic electronics is now increasingly focusing on the development of new sustainable methodologies that allow to prepare active materials in a more efficiently way, caring further on safety and sustainability associated with production processes. The immediate approach applicable consist on the removal, or at least on the minimization, of harmful and toxic substances commonly employed within standard processes. The big elephant in the room in the synthesis of active materials is the amount of organic solvent employed, which could ideally be reduced by using aqueous solution of surfactants: in these nano/micro heterogeneous environments organic transformations can happen and often with unprecedent efficiency. Clearly, the process occur not through the dissolution of the reagents (starting materials and catalyst) but from their dispersion in water. Kwon as “micellar catalysis”, this strategy has proven to be highly effective on improving sustainability becoming a prominent topic in modern organic synthesis. In particular, the micellar catalysis strategy is compatible with the most common modern strategies employed for C-C and C-heteroatom bonds forming reactions and allow to perform reactions with high yields, in water and under very mild conditions. Nonetheless, the use of such method in the field of organic semiconductors is still limited, with only few relevant examples reported in literature concerning the preparation of π-conjugated molecular and polymeric materials. This Thesis describes the importance of introducing sustainability in the synthesis of organic semiconductors, satisfying several principles of the green chemistry guidance. Our research purpose is not to provide an exhaustive list of examples of such chemistry, but rather to identify a few key developments in the field that seem especially suited to large-scale synthesis. Then, the discussion will consider the synthetic approaches typically employed to access semiconducting materials with extended π-conjugated structures. In particular, the discussion will involve the well-known Pd-catalysed cross-coupling techniques. Finally, the topic of the work will focus on micro-heterogeneous environments as a new tool for introducing sustainability in the preparation of active materials in water, satisfying several criteria relevant to green chemistry. On my opinion, the micellar catalysis approach constitute today the more promising method to lower the overall cost and environmental impact in the production of organic semiconductors without affecting yields, purity, and device performance.