High-yield syntheses of doubly 2,7-dialkynylpyrene-threaded photostable [8]rotaxanes exhibiting extremely bright circularly polarized luminescence

Abstract

Circularly polarized luminescence (CPL) emitters garner much interest due to their potential applications in chiroptical materials. While many organic CPL emitters have been reported, their preparation often requires low-yield reactions and laborious optical resolution steps. In this study, we demonstrated a cooperative rotaxane approach to synthesize CPL emitters with desirable properties in high yields. We designed doubly 2,7-dialkynylpyrene-threaded [8]rotaxanes with two γ-cyclodextrins and four cucurbit[6]urils as ring components. Although these [8]rotaxanes have heavily complicated interlocked structures, their syntheses were achieved in 67–77% isolated yields as a single isomer utilizing a cooperative capture strategy. These [8]rotaxanes exhibited high luminescence quantum yields Φ_lum of 0.40–0.47 and large |g_lum| values of 1.1–1.9 × 10⁻² in an aqueous solution. Considering ϵ = 2.2–2.5 × 10⁵ M⁻¹cm⁻¹, the CPL brightness (B_CPL = ϵ × Φ_lum × |g_lum|/2) values of 569–836 were as bright as the highest ones of reported organic CPL emitters. Owing to the insulation of the alkynylpyrene cores against outside molecules by the ring components, the [8]rotaxanes showed outstanding photo- and thermal-stability in solutions. The [8]rotaxanes might have the potential to be CPL emitters suitable for future optical materials.