A general and mild synthetic method for fused-ring electronic acceptors

Fused-ring electronic acceptors (FREAs) have transformed the field of organic solar cells. However, the prevailing syntheses of FREAs suffer from low yield, difficulty in separation, and high cost. Here, we report new and streamlined syntheses with three distinctive key steps. First, a universal approach to fuse neighboring aromatic units via a single carbon atom is demonstrated with ytterbium triflate and boron trifluoride as the catalysts. This approach allows the incorporation of diverse side-chain combinations. Second, nitrogen atom fusing neighboring aromatics is realized by using oxo-molybdenum catalyst, featuring lower reaction temperatures and enhanced yields. Third, an organic catalyst, proline, is identified to catalyze the aldol condensation with high yield to afford the most typical FREAs having acceptor-donor-acceptor (ADA) configurations. Our new chemistries enable easy syntheses of a wide range of FREAs, substantially expanding the scope and availability of these coveted materials at reduced synthetic cost, particularly for organic electronics.