Synthesis and chiroptical properties of macrocycles composed of chiral spirobifluorenes linked by π-conjugated spacers

Abstract Organic circularly polarized luminescence materials have attracted considerable attention. In evaluating their performance, not only the dissymmetry factor (|glum|) but also their light absorption and emission efficiency are important. As the comprehensive metric that accounts for 3 factors, the brightness of circularly polarized luminescence (BCPL) has been proposed. In this study, aiming to achieve high BCPL, chiral macrocycles 2-[3] and 2-[4], which are a cyclic trimer and tetramer composed of chiral spirobifluorene derivatives connected by biphenyl spacers, were designed. The chiral macrocycles 2-[3] and 2-[4] were successfully synthesized. Absorption spectra of 2-[3] and 2-[4] showed high molar extinction coefficients (2.05 × 105 and 2.67 × 105 M−1 cm−1, respectively). Both compounds exhibited intense violet fluorescence, with high quantum yields of approximately 90%. The |glum| values were approximately 2.0 × 10−3 for both compounds. Notably, the BCPL values were 177 M−1 cm−1 for 2-[3] and 261 M−1 cm−1 for 2-[4], representing relatively high values among organic small-molecule emitters.