Aggregation-induced Radical and Room-Temperature Ferromagnets of Diketopyrrolopyrrole Derivatives

It is extremely challenging to prepare room-temperature ferromagnet (RTF) semiconductors as it is of great importance for development of electronic and spintronic devices in future. Herein, we report that significant radical signals were detected in three low bandgap small molecules based on diketopyrrolopyrrole derivatives, since these molecules have an open-shell singlet diradical ground state. A new mechanism of aggregation-induced radical (AIR) was proposed to interpret the origin of radical signals and the transformation from the aromatic structure to the quinoid-diradical (Q-D) structure in D-A type low bandgap organic semiconductors. More importantly, the molecule Py-TTDPP exhibited obvious ferromagnetism at room temperature, which also showed extensive radical signals due to the thermally-excited triplet state in aggregation state. It was the first report on the RTF based on neutral organic small molecule semiconductors. Our findings unambitiously indicate the coming of the room-temperature magnets based on organic small molecule radicals in future.