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 <i>p</i>- and <i>n</i>-type, and light-absorbing materials. In this work, we report the synthesis and characterization of diindeno-fused derivatives of dibenzo[<i>b,def</i>]chrysene and dibenzo[<i>def,mno</i>]chrysene, obtained from vat orange 1 (<b>VO1</b>) and vat orange 3 (<b>VO3</b>), 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 <b>VO3</b> derivative (<b>1-OR</b>). 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 <b>VO1</b> scaffold generated diradical intermediates that rapidly oxidized to diketone products (<b>2'-TIPS</b> and <b>2'-OR</b>), <b>VO3</b> 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.