Synthesis of Chrysene-Based Nanographenes by a Successive APEX Reaction.

Chrysene-based nanographenes (ChrNGs), despite their relatively small structures, have been reported to exhibit low highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gaps and strong long-wavelength fluorescence, making them attractive for various applications. However, the precise synthesis of ChrNGs remains challenging, and their availability is limited compared with other classes of nanographenes. Herein, we report the synthesis of novel ChrNGs by a successive annulative π-extension (APEX) reaction. Using diphenylacetylene and benzonaphthosilole in a Pd/o-chloranil catalytic system, successive APEX afforded ChrNGs of various lengths and degrees of oxidation. Furthermore, exhaustive separation and further π-extension by cyclodehydrogenation afforded ChrNGs with more flat and rigid structures. Photophysical measurements of the obtained ChrNGs showed a variety of absorption and emission properties, including intense multicolor emission.