Benzoyl-xanthenoxanthenes: Versatile Chromophores for Light-Engaging Applications

In this work, we present a modular donor–acceptor strategy that produces oxidatively stable, benzoyl-fused peri-xanthenoxanthene (PXX) ribbons with near-infrared (NIR) emission and light-harvesting properties. Benzoyl fusion at the pseudo-peri positions, achieved through intramolecular Friedel–Crafts planarization, creates the first benzoylfunctionalized PXX monomers, dimers, and trimers that exhibit deep red–NIR absorption and emission without significantly raising the HOMO level. The ribbons display strong, tunable absorption and fluorescence bands, with up to 63% of emission in the NIR and an NIR fluorescence quantum yield (Φ reaching 0.36 in solution). Lewis adducts formed between boron-based Lewis acid and the carbonyl acceptor sites further enhance the electron-accepting nature of the ketones, producing pure NIR emission (Φ ≈ 15%–16%). Spectroelectrochemical investigations uncover reversible electrochromism and electrofluorochromism, supporting redox-gated switching and NIR absorption signatures, useful for sensing and display technologies. When embedded in a nematic liquid crystal phase, the ribbons function as cascaded Förster resonance energy transfer (FRET) antennas, achieving near-quantitative single-step energy transfer (Φ = 0.97) and highly efficient two-step transfer (Φ = 0.70), enabling directional energy funneling. Their complementary absorption broadens the excitation window to cover the entire visible spectrum, making them highly efficient panchromatic light-harvesting materials.