Boron‐Doped Organic Diradicaloids with the Indenofluorene and Fluorenofluorene Cores for Photothermal Conversion Materials †

Comprehensive Summary Organic diradicaloids have attracted great interest owing to their unique open‐shell structures and optical, electronic and magnetic properties. Incorporation of boron atoms may provide organoboron diradicaloid systems, but their synthesis is quite challenging owing to inherent reactivity caused by the boron atom and radical center. In this work, we report the design and synthesis of boron‐doped PH 1 and its quinoidal π‐extended derivative 2 , both of which feature fusion of two boracyclic motifs onto the indeno[1,2‐ b ]fluorene and fluoreno[3,2‐ b ]fluorene cores, respectively. They have the linearly extended C 40 B 2 and C 44 B 2 polycyclic π‐skeletons, respectively. Theoretical and experimental studies reveal their open‐shell singlet diradical states, contributed by the central quinoidal conjugated structures. These two molecules show a few intriguing properties, such as excellent stability, magnetic activity and four‐step reversible redox activity, as well as broad light absorption. Notably, the solid of 2 exhibits the photothermal conversion capability and superior photostability, and the as‐prepared surface solar evaporator displays efficient water evaporation performance. This study thus not only enriches the molecular systems of organic heterocyclic diradicaloids, but also provides a promising organic photothermal material for applications in the energy and biomedical fields.