Synthesis of Diindeno-Fused Dibenzochrysenes: A Route to Low-Bandgap Polycyclic Aromatic Hydrocarbons

Low-bandgap polycyclic aromatic hydrocarbons (PAHs) are of great interest for applications in organic electronics, where they can serve as efficient semiconductors, both p - and n -type, and light-absorbing materials. In this work, we report the synthesis and characterization of diindeno-fused derivatives of dibenzo[ b,def ]chrysene and dibenzo[ def,mno ]chrysene, obtained from vat orange 1 ( VO1 ) and vat orange 3 ( VO3 ), respectively. Through strategic fusion of indene units, we successfully reduced the optical bandgap of these PAHs, achieving values as low as 1.65 eV for the VO3 derivative ( 1-OR ). The introduction of triisopropylsilyl (TIPS) and dodecyloxy (OR) substituents provided solubility and influenced the regioselectivity of the intramolecular Friedel–Crafts cyclization. While diindeno-fusion of the VO1 scaffold generated diradical intermediates that rapidly oxidized to diketone products ( 2′-TIPS and 2′-OR ), VO3 derivatives retained their structure, exhibiting deep-blue coloration and strong π–π* absorption in the visible region. Optical, electrochemical, and computational analyses (including DFT and TD-DFT studies) revealed significant modulation of the electronic structure, with Clar sextet analysis and nuclear independent chemical shift/electron density of delocalized bonds calculations supporting the impact of indenyl fusion on aromaticity and bandgap tuning. These findings highlight the potential of indene fusion for designing low-bandgap, electron-accepting PAHs for organic electronic applications.