Dearomatizing [4+1] Spiroannulation of Naphthols: Discovery of Structurally Non-Traditional Thermally Activated Delayed Fluorescent Materials.

The development of streamlined synthetic routes to spirofluorene derivatives, in particular those with a donor-acceptor (D-A) system, is an appealing task in the field of organic functional materials. In this work, we disclose a palladium-catalyzed direct [4+1] spiroannulation of ortho-C-H bonds of naphthols with cyclic diaryliodonium salts to construct spirofluorenyl naphthalenones (SFNP) under mild reaction conditions. This spiroannulation not only directly transforms the hydroxyl group into the carbonyl group, but also tolerates reactive functional groups such as the halo groups, which provide an opportunity to rapidly assemble structurally non-traditional thermally activated delayed fluorescent (TADF) materials that feature a carbonyl group with an adjacent spirofluorenyl unit as the acceptor. As an illustrated example, the OLED device utilizing the assembled DMAC-SFNP as the host material exhibits a low turn-on voltage of 2.5 V and an ultra-high external quantum efficiency of 32.2%. This work not only gives us an inspiration for designing structurally non-traditional TADF materials, but also displays the charm of C-H activation as a revolutionary synthetic strategy in the innovation of optoelectronic materials.