Diboron- and digermanium-doped dihydrodibenzohexacenes: Ge–B exchange to access boron-doped extended acenes

Abstract

Incorporation of main-group atoms into the backbone of polycyclic aromatic hydrocarbons offers an effective strategy to modulate their electronic structures. Boron and germanium doping is particularly attractive for enhancing optoelectronic and electrochemical properties. However, regioselective incorporation of these elements into extended π-conjugated systems remains limited due to synthetic challenges and stability issues. Herein, we report the synthesis of isomeric series of digermanium- (2 and 6) and diboron- (4 and 8) embedded dihydrodibenzohexacenes. The molecular structures of four compounds were confirmed by single-crystal X-ray diffraction, revealing curved backbones for the digermanium-doped compounds 2 and 6, whereas the diboron analogues 4 and 8 display planar backbone incorporating two weakly antiaromatic C₅B rings. All compounds show efficient photoluminescence in both the solution- and solid-state, spanning the wide spectral regions from blue to orange. Electrochemical studies of 4 and 8 reveal two quasi-reversible reduction processes, with the pseudo-para diboron-substituted isomer 8 exhibiting slightly anodically-shifted reduction potentials. These results demonstrate that diboron and digermanium doping provides a promising platform for the development of stable, emissive, and redox-active polycyclic aromatic hydrocarbons.