(Invited) Spironanographenes: Chemospecific Scholl Reaction, Unexpected Formation of Bilayers and Donor-Acceptor Behavior

Abstract

Bottom-up benchtop synthesis of nanometric fragments of graphene, molecular nanographenes (NGs), allows the design and monodisperse preparation of molecules with structures, and thus properties, at will. The most commonly employed methodology has mainly consisted in the π-extension of a central scaffold followed by a graphitization step, in which the honeycomb pattern of the final molecular nanographene is formed. The vast majority of syntheses involving molecular nanographenes, employ the Scholl reaction as graphitization step. This dehydrogenative C–C coupling, first described by Roland Scholl in 1910, has now become one of the most powerful reactions in NGs synthesis, although its mechanism pathway is still under debate.In this connection, in early 2023, we reported a chemospecific Scholl reaction depending on the electronic nature of the central scaffold. The formation of stabilized trityl cations using anthracene as central scaffold, led to the formation of spirocycles under Scholl reaction conditions, without interrupting the graphitization process, for the first time (Figure a).1 In contrast, the destabilization of the trityl cation by including fluorine atoms afforded helically arranged NGs (Figure b).2 Furthermore, in order to study the electronic communication in spironanographenes, recently we have extended the π-system of spirobifluorene yielding to two-fold chiral spironanographenes (Figure c). Surprinsingly, the π-π interactions of the graphitic moieties avoid their orthogonal disposition yielding a bilayer that could lead to important electronic features due to the overlap of the two fragments (Figure d).3 [1] P. Izquierdo-García, J. M. Fernández-García, J. Perles, I. Fernández, N. Martín. Angew. Chem. Int. Ed. 2023, 62, e202215655[2] P. Izquierdo-García, J. M. Fernández-García, I. Fernández, J. Perles, N. Martín. J. Am. Chem. Soc. 2021, 143, 11864–11870.[3] P. Izquierdo-Garcia, J. M. Fernandez-Garcia, S. Medina Rivero, M. Samal, J. Rybacek, L. Bednarova, S. Ramirez-Barroso, F. J. Ramirez, R. Rodriguez, J. Perles, D. Garcia-Fresnadillo, J. Crassous, J. Casado, I. G. Stara, N. Martin, J. Am. Chem. Soc. 2023, 145, 11599. Figure 1