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.