From Targeted Synthesis to Serendipitous Discovery: Transforming Perfluorotoluene into Discotic Liquid Crystals and...

This study develops a one-pot synthetic system that concurrently produces two classes of functional materials via a previously unobserved transformation of perfluorotoluene under nucleophilic conditions. Building on prior work with fluorinated discotic systems, the reaction of 2,2'-dilithio-1,1'-biaryls with perfluorotoluene (C₆F₅-CF₃) furnishes trifluoromethylated trifluorotriphenylene derivatives (TPFn, n = 1-4, 6, 8, 10, 8/2) alongside structurally distinct dearomatized spirofluorene analogues (TPFn-1). The formation of the spirofluorene compounds points to a competing pathway beyond classical aryl nucleophilic substitution. Based on structural evidence, a dearomatization process involving cleavage of four C-F bonds (one from the pentafluorophenyl ring and three from the CF₃ group) and subsequent formation of new C-C bonds is proposed to account for the formation of the spiro-fused architecture. This side reaction sheds light on the moderate yields of the target TPFn series and highlights the complex reactivity of perfluorotoluene with 2,2'-dilithio-1,1'-biaryls. All TPFn compounds form thermally stable hexagonal columnar (Col_hex) mesophases with large liquid-crystalline ranges, along with a strong modulation of the clearing temperatures with alkoxy chain lengths. Despite the presence of the bulky lateral CF₃ group, the transition temperatures are surprisingly not greatly affected when compared to previously synthesized 4F-TPn homologous compounds (with no CF₃ groups). Structural analysis, supported by X-ray crystallography of ditert-butyl model compound (tBuTPF), validates the molecular design and packing. This work thus provides a practical one-pot route to potentially fluorinated discotic semiconductors while revealing a competing transformation that advances the understanding of polyfluorinated arene chemistry and offers access to novel spiro-fused molecular architectures.