Structural Diversity in Scholl Reactions of a Nitrogen-Bridged 1-Anthryl Dimer: Formation of Dinaphtho[a,i]carbazole and Higher Oligomers

A nitrogen-bridged 1-anthryl dimeric precursor was synthesized and subjected to oxidative cyclization (Scholl reaction) to examine how reaction conditions influence product selectivity and molecular structure. Oxidation using anhydrous FeCl3 or chloranil/TfOH led to intramolecular cyclization, yielding fused-ring products, including a novel dinaphtho[a,i]carbazole derivative (1L) and its dimer (1LD). In contrast, treatment with DDQ/TfOH predominantly facilitated intermolecular coupling between precursor molecules, producing a chain-type dimer (2D). Single-crystal X-ray diffraction of 1LD confirmed dimerization at the C4 positions of the anthracene units. UV-vis absorption and fluorescence spectroscopy revealed that 1L and 1LD exhibit blue-shifted emission and larger Stokes shifts relative to 2 and 2D, highlighting the effect of cyclization on the electronic structure. Cyclic voltammetry indicated that 1L possesses higher oxidation potentials than 2, consistent with the electron-deficient character of the fused π-conjugated framework. In contrast, 2D exhibited lower oxidation potentials, reflecting enhanced electron-donating ability and a greater tendency for further oxidative oligomerization. These findings demonstrate that precise modulation of oxidative conditions enables selective control over intramolecular versus intermolecular coupling pathways, providing access to structurally diverse nitrogen-containing polycyclic aromatic hydrocarbons.