Synthesis and Chiroptical Properties of Radially Extended Carbazole with Chiral [2.2]Paracyclophane Core

[2.2]Paracyclophanes ([2.2]PCs) with substituents at specific positions possesses planar chirality and stands as a promising building unit for the development of chiroptical materials associated with polarized light. However, one of the easily accessible starting materials, bromo-substituted [2.2]PC, shows low reactivity, and effective methods for pi-extension of planar chiral [2.2]PC are limited. Herein, an effective pi-extension method has established for chiral [2.2]PC with four substitutions from 4,7,12,15-tetrabromo[2.2]PC. This has led to tetrakis(trimethylsilylphenyl)-[2.2]PC that serves as a versatile building resource for radial-type chiral pi-conjugated compounds with a [2.2]PC core. In this study, synthesizing compounds are further succeeded with the introduction of carbazole (Cbz4-[2.2]PC and tBuCbz4-[2.2]PC) and investigated their chiroptical properties and chiral induction ability in achiral pi-conjugated polymers. A thin film of [Poly[9,9-dioctylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,7-diyl)]] (F8BT) with 3wt% Cbz4-[2.2]PC prepared by spin-coating exhibits circularly polarized luminescence (CPL) properties with a high dissymmetry factor (|glum| = 0.01), which is much higher than that of Cbz4-[2.2]PC in CH2Cl2 solution. By contrast, the doped film of F8BT with 3wt% tBuCbz4-[2.2]PC exhibited only weak CPL properties. In addition, these chiral compounds show facile redox properties owing to the presence of carbazole units. Furthermore, Cbz4-[2.2]PC undergoes electropolymerization to produce an insoluble thin film on the electrode. A newly developed coupling reaction using boroxine derivatives efficiently gives a planar chiral [2.2]paracyclophane with four radially attached carbazoles. This compound allows the higher-order structure of F8BT in thin films to become chiral with a small amount of doping, resulting in thin films that exhibit remarkable CPL properties. image