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

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.

N-Doped Nonalternant Nanoribbons with Excellent Nonlinear Optical Performance.

Two novel N-doped nonalternant nanoribbons (NNNR-1 and NNNR-2) featuring multiple fused N-heterocycles and bulky solubilizing groups were prepared via bottom-up solution synthesis. NNNR-2 achieves a total molecular length of 33.8 Å, which represents the longest soluble N-doped nonalternant nanoribbon reported to date. The pentagon subunits and doping of N atoms in NNNR-1 and NNNR-2 have successfully regulated their electronic properties, achieving high electron affinity and good chemical stability enabled by the nonalternant conjugation and electronic effects. When applied a laser pulse of 532 nm, the 13-rings nanoribbon NNNR-2 shows outstanding nonlinear optical (NLO) responses, with the nonlinear extinction coefficient of 374 cm GW-1 , much higher than those of NNNR-1 (96 cm GW-1 ) and the well-known NLO material C60 (153 cm GW-1 ). Our findings indicate that the N-doping of nonalternant nanoribbons is an effective strategy to access another type of excellent material system for high-performance NLO applications, which can be extended to construct numerous heteroatom-doped nonalternant nanoribbons with fine-tunable electronic properties.