Inner Bond Cleavage of Nanographenes: Rational Strategy for Creating and Integrating Figure-Eight Structures

The beautiful structures of conjugated -systems with three-dimensional shapes have stimulated the curiosity of scientists and contributed to the evolution of science and technology. However, the construction of such distorted structures by multistep transformations often accompanies with undesirable side reactions. Consequently, the mass production of nonplanar-systems has still been challenging despite its utility for accelerating interdisciplinary research. In this article, we demonstrate that the inner double bond cleavage of nanographenes is a rational strategy for creating figure-eight molecules. Treatment of dibenzo[g,p]chrysene (DBC) with sodium dichromate dihydrate selectively cleaves the inner double bond to afford cyclobisbiphenylenecarbonyl (CBBC), which adopts a figure-eight structure. This transformation is scalable up to 23 g. This protocol is also applicable to brominated DBC derivatives. The Suzuki-Miyaura cross-coupling reactions of thus obtained brominated CBBCs afforded the corresponding p-tolyl derivatives, which emit circularly polarized luminescence (CPL) with high g values of more than 0.01. CBBC exhibits various intriguing properties: (1) the spontaneous resolution to afford a conglomerate, (2) configurational stability at room temperature, (3) the formation of a triplet excitation state upon photo-irradiation, and (4) the transformations of carbonyl groups. We also examined the oxidative inner bond cleavage of larger nanographenes, which furnished three non-planar -systems consisting of two figure-eight subunits. These highly distorted structures are difficult to construct by the conventional bottom-up approach, thus highlighting the power of the oxidative inner bond cleavage strategy.