Sustainable production of carbazole-based BioAIEgens from lignin major motifs

The catalytic conversion of lignin into heterocyclic aromatic compounds holds significant promise not only for expanding lignin's utility in pharmaceutical synthesis but also for imparting luminescent properties to downstream lignin products. However, the challenge lies in devising compatible catalytic conditions for selectively cleaving aromatic ether bonds and forming C–N bonds. In this study, we present a new approach to synthesizing functionalized carbazole derivatives from lignin phenolic β-O-4 model linkages using a one-pot, two-step method. Through a [3 + 1 + 2] benzene cyclization reaction involving lignin β-O-4 model compound, indole-3-carbaldehyde, and 3-chloropropiophenone catalyzed by cost-effective CuCl2·2H2O, we achieved yields of carbazole derivatives up to 90%, highlighting the economic viability of our approach. Our protocol is versatile, accommodating various reaction conditions, including selective cleavage of the C–O bond, aldol condensation, dehydrochlorination of β-chloro ketones, Diels–Alder addition, and dehydroaromatization reactions. Additionally, the resulting carbazole derivatives exhibit favorable twisted-intramolecular charge transfer (TICT) and aggregation-induced emission (AIE) effects. This method offers a sustainable and practical strategy for synthesizing lignin-based carbazoles, with economic advantages in terms of the catalysts and precursors, thereby advancing lignin's application in luminescent materials.