A Simple Molecular Design Strategy for Delayed Fluorescence toward 1000 nm.

Harnessing the near-infrared (NIR) region of the electromagnetic spectrum is exceedingly important for photovoltaics, telecommunications, and the biomedical sciences. While thermally activated delayed fluorescent (TADF) materials have attracted much interest due to their intense luminescence and narrow exchange energies (ΔEST), they are still greatly inferior to conventional fluorescent dyes in the NIR, which precludes their application. This is because securing a sufficiently strong donor-acceptor (D-A) interaction for NIR emission alongside the narrow ΔEST required for TADF is highly challenging. Here, we demonstrate that by abandoning the common polydonor model in favor of a D-A dyad structure, a sufficiently strong D-A interaction can be obtained to realize a TADF emitter capable of photoluminescence (PL) close to 1000 nm. Electroluminescence (EL) at a peak wavelength of 904 nm is also reported. This strategy is both conceptually and synthetically simple and offers a new approach to the development of future NIR TADF materials.