Scholl Reaction of Perylene‐Based Polyphenylene Precursors under Different Conditions: Formation of Hexagon or Octagon?

Luminescent Chiral Furanol-PAHs via Straightforward Ni-Catalysed Csp2 -F Functionalization: Mechanistic Insights into the Scholl Reaction

Here we report the stepwise synthesis of new nanographenes (NGs) and polycyclic aromatic hydrocarbons (PAHs) obtained via Scholl ring fusion applied at aromatic homologation compounds, which are obtained through one-step Ni-catalysed Csp2 -F functionalization. The latter are rapidly accessed valid precursors for the Scholl reaction, and screening of experimental conditions allowed us to describe for the first time furanol-bearing PAHs. Mechanistic insights are obtained by DFT to rationalize the formation of the furanol PAHs under moderately acidic conditions. All PAHs and NGs synthesized show moderate/weak fluorescent properties, and all PAHs crystallized show some degree of curvature and are obtained as racemic mixtures. Enantiomeric separation by chiral HPLC of one furanol-bearing PAH allowed the study of their chiroptical CD properties.

Synthesis of Bioctacene-Incorporated Nanographene with Near-Infrared Chiroptical Properties

We report the synthesis of a hexabenzoperihexacene (HBPH) with two incorporated octacene substructures, which was unambiguously characterized by single-crystal X-ray analysis. The theoretical isomerization barrier of the (P,P)-/(P,M)-forms was estimated to be 38.4 kcal mol^-1 , and resolution was achieved by chiral HPLC. Notably, the enantiomers exhibited opposite circular dichroism responses up to the near-infrared (NIR) region (830 nm) with a high g_abs value of 0.017 at 616 nm. Moreover, HBPH demonstrated NIR emission with a maximum at 798 nm and an absolute PLQY of 41 %. The excited-state photophysical properties of HBPH were investigated by ultrafast transient absorption spectroscopy, revealing an intriguing feature that was attributed to the rotational and/or conformational dynamics of HBPH after excitation. These results provide new insight into the design of chiral nanographene with NIR optical properties for potential chiroptical applications.

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

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-[9,10,1,2,3-pqrst]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.

Synthesis of Highly Luminescent Chiral Nanographene

Chiral nanographenes with both high fluorescence quantum yields (Φ_F ) and large dissymmetry factors (g_lum ) are essential to the development of circularly polarized luminescence (CPL) materials. However, most studies have been focused on the improvement of g_lum , whereas how to design highly emissive chiral nanographenes is still unclear. In this work, we propose a new design strategy to achieve chiral nanographenes with high Φ_F by helical π-extension of strongly luminescent chromophores while maintaining the frontier molecular orbital (FMO) distribution pattern. Chiral nanographene with perylene as the core and two dibenzo[6]helicene fragments as the wings has been synthesized, which exhibits a record high Φ_F of 93 % among the reported chiral nanographenes and excellent CPL brightness (B_CPL ) of 32 M^-1  cm^-1 .

Oxidative Cyclodehydrogenation of Trinaphthylamine: Selective Formation of a Nitrogen-Centered Polycyclic π-System Comprising 5- and 7-Membered Rings

We describe a new type of nitrogen-centered polycyclic scaffold comprising a unique combination of 5-, 6-, and 7-membered rings. The compound is accessible through an intramolecular oxidative cyclodehydrogenation of tri(1-naphthyl)amine. To the best of our knowledge this is the very first example of a direct 3-fold cyclization of a triarylamine under oxidative conditions. The unusual ring fusion motif is confirmed by X-ray crystallography and the impact of cyclization on the electronic and photophysical properties is investigated both experimentally and theoretically based on density-functional theory (DFT) calculations. The formation of the unexpected product is rationalized by detailed mechanistic studies on the DFT level. The results suggest the cyclization to occur under kinetic control via a dicationic mechanism.

A Near-Infrared Absorbing and Emissive Quadruple Helicene Enabled by the Scholl Reaction of Perylene

Herein we report the synthesis, structural analysis, optical and chiroptical properties of a novel quadruple helicene, which has two [6] and two [7]helicene moieties fused in a contorted framework of 92 sp 2 carbon atoms.  It was synthesized by the Scholl reaction of a perylene-containing substrate with the formation of eight carbon-carbon bonds on the perylene unit in a single synthetic operation. Chemical oxidation of the quadruple helicene with tris(4-bromophenyl)ammoniumyl hexachloroantimonate resulted in an air-stable dication, which exhibits the same helicity in its four helicene moieties as unambiguously identified by single crystal X-ray crystallography. The quadruple helicene exhibits unusual near-infrared absorption and emission with absorption and emission maxima at 848 nm and 977 nm, respectively, and its isolated enantiomers exhibit electronic circular dichroism in the near-infrared and visible light regions.

Transformation of Crowded Oligoarylene into Perylene-Cored Chiral Nanographene by Sequential Oxidative Cyclization and 1,2-Phenyl Migration

Synthetic innovation for constructing sophisticated nanographenes is of fundamental significance for a variety of advanced applications. Herein, we report a distinctive method to prepare π-extended chiral nanographenes with 29 benzenoid rings and two helical breaches from a highly crowded perylene-cored oligoarylene precursor. Under Scholl's conditions, the reaction predominantly involves the regioselective and sequential cyclization in the peri- and bay regions of the perylene core, and the complanation of the 1-phenyl[5]helicene intermediate module via 1,2-phenyl migration. The resulting chiral nanographenes are configurationally stable at 180 °C due to the high diastereomerization barriers of ca. 45 kcal mol^-1 . These molecules also possess globally delocalized π-systems with low HOMO/LUMO gaps, leading to nearly panchromatic absorption, intensive electronic circular dichroism signals and deep-red circularly polarized luminescence.

Carbazole-Fused Polycyclic Aromatics Enabled by Regioselective Scholl Reactions

The synthesis of new carbazole-fused polycyclic aromatics with interesting geometry and useful properties was explored using Scholl reactions. As found from the Scholl reactions of substrates having two carbazole units linked at different positions through o-phenylene, oxidative coupling of carbazole units occurred in a regioselective manner with new carbon-carbon bonds preferably formed at C3 and C4 in N-alkyl carbazoles. A new N-containing aromatic bowl was characterized by single-crystal X-ray crystallography, and new p-type organic semiconductors exhibited field effect mobility of up to 0.070 cm²  V^-1  s^-1 in solution-processed thin-film transistors.