Electronic Control of the Scholl Reaction: Selective Synthesis of Spiro vs Helical Nanographenes

Abstract

Scholl oxidation has become an essential reaction in the bottom-up synthesis of molecular nanographenes. Herein, we describe a Scholl reaction controlled by the electronic effects on the starting substrate (1 a, b). Anthracene-based polyphenylenes lead to spironanographenes under Scholl conditions. In contrast, an electron-deficient anthracene substrate affords a helically arranged molecular nanographene formed by two orthogonal dibenzo[fg,ij]phenanthro-[9,10,1,2,3pqrst]pentaphene (DBPP) moieties linked through an octafluoroanthracene core. Density Functional Theory (DFT) calculations predict that electronic effects control either the first formation of spirocycles and subsequent Scholl reaction to form spironanographene 2, or the expected dehydrogenation reaction leading solely to the helical nanographene 3. The crystal structures of four of the new spiro compounds (syn 2, syn 9, anti 9 and syn 10) were solved by single crystal X-ray diffraction. The photophysical properties of the new molecular nanographene 3 reveal a remarkable dual fluorescent emission.

Helical Bilayer Nanographenes: Impact of the Helicene Length on the Structural, Electrochemical, Photophysical, and Chiroptical Properties

“…This synthetic control allows, in turn, the fine-tuning of chemical, optical, and electronic properties . In the last recent years, a broad variety of molecular NGs have been synthesized by this methodology, covering a wide range of shapes, from the straightforward planar NGs to curved, twisted, or helically arranged molecular NGs . The incorporation of curvature, strain, or helicity in NGs may introduce asymmetry in the structures, leading to the appearance of stereoisomeric forms, that open the possibility of new applications derived from their chiroptical properties …”

Electrochemical Syntheses of Polycyclic Aromatic Hydrocarbons (PAHs)

“…Thereafter, the DDQ/H + system was repeatedly utilized for Scholl reactions to produce diverse PAHs. [89][90][91][92][93][94][95][96][97] However, a stoichiometric amount of DDQ was typically needed. The Figure 5.…”

“…Thereafter, the DDQ/H + system was repeatedly utilized for Scholl reactions to produce diverse PAHs. [ 89–97 ] However, a stoichiometric amount of DDQ was typically needed. The repreparation of DDQ from the DDQ‐H 2 is theoretically feasible, but this undoubtedly adds cumbersome work.…”

Construction of hexabenzocoronene-based chiral nanographenes

“…Except for the helicene-based chirality, chirality stemming from a chiral axis is relatively rare in designing chiral NGs. Notably, Martín and co-workers reported a new family of chiral NGs, which constituted by two orthogonal dibenzo[ fg , ij ]phenanthro-[9,10,1,2,3- pqrst ]pentaphene (DBPP) units covalently connected through tetrafluorophenylene ( 61 ) [ 49 ] or octafluoro-9,10-anthracenylene ( 65 ) [ 50 ] linkers. The synthesis started with a double Pd-catalyzed Sonogashira cross-coupling reaction of phenylacetylene 50 and 1,4-dibromotetrafluorobenzene.…”