Thiapillar[6]arene: Synthesis, Functionalization, and Properties

The design and synthesis of new macrocycles with well-defined cavities represent a promising avenue for the development of new supramolecular hosts. Moreover, the ability to diversify a macrocycle through chemical manipulations enables the fine-tuning and tailoring of properties. In this report, the synthesis and functionalization of thiapillar[6]arene, a pillar[6]arene analogue in which the bridging methylene groups are replaced by sulfurs, are described. First, we demonstrate the scalable synthesis of the parent thiapillar[6]arene. Next, the diversification of thiapillar[6]arene is demonstrated via functionalization of the phenols and oxidation of the sulfur atoms. The solid-state structures of two thiapillar[6]arene derivatives are reported, and the effect of sulfur oxidation state on the macrocyclic conformation is discussed. All sulfone derivatives described were found to demonstrate high luminescence quantum yields (ΦF = 0.43–0.66) in CH2Cl2 with emission maxima between λ = 404 and 462 nm. Lastly, assessment of the electrochemical properties of the sulfone derivatives by square-wave voltammetry revealed electron-accepting ability owing to the oxidation of the sulfur atoms, with four reduction events observed for the analogues surveyed. Overall, this work implicates thiapillar[6]arene as a modular scaffold amenable for further applications in host–guest chemistry and sensing.