Non‐alternant Benzodifluoranthene Tetraimides from 7,8,9,10‐Fluoranthene Diimides: Synthesis, Structure, and Optical‐Limiting Properties

Abstract

A novel tetraimide‐functionalized non‐alternant π‐conjugated system, namely, benzodifluoranthene tetraimides (BDFTI), has been designed and synthesized through highly efficient UV‐photocyclization of a vinyl‐bridged fluoranthene diimide dimer (i.e., FDI‐V). The synthesis of FDI‐V starts from a straightforward three‐step route to produce novel 7,8,9,10‐fluoranthene diimide (FDIs) building‐blocks, followed by nearly complete bromination and then Stille‐coupling reaction to give the desired dimer. The analysis by X‐ray crystallography confirms a near‐coplanar geometry for FDIs, while BDFTI shows a U‐shaped and distorted backbone configuration proven by theoretical optimizations. The tetraimide BDFTI exhibits several advantages over the FDI cores, including an extended absorption band and a red‐shift in photoluminescence spectra. This enhancement can be attributed to the presence of additional electron‐deficient imide units, which promotes increased intramolecular charge transfer and improved electron affinity. All the imides show a local aromatic characteristic owing to the incorporation of pentagon rings in the π‐frameworks. The fully fused BDFTI exhibits nonlinear optical properties as analyzed by the open‐aperture Z‐scan technique, demonstrating superior optical‐limiting performance compared to vinyl‐bridged FDI‐V. The versatile UV‐photocyclization chemistries provide a pathway for developing complex and unique multiimide‐functionalized π‐conjugated systems, paving the way for creating high‐performance optical‐limiting materials.