Two new highly charged catenanes-namely, mHeC·6PF6 and mHoC·6PF6-were synthesized by exploiting radical host-guest templation between derivatives containing BIPYâ\¢+ radical cations and the meta analogue of cyclobis(paraquat-p-phenylene). In contrast to related catenanes that have been isolated as air-stable monoradicals, both mHeC·6PF6 and mHoC·6PF6 exist as air-stable singlet bisradicals, as evidenced by both X-ray crystallography in the solid state and EPR spectroscopy in solution. Electrochemical studies indicate that the first two reduction peaks of these two catenanes are shifted significantly to more positive potentials, a feature which is responsible for their extraordinary stability in air. The mixed-valence nature of the mono- A nd bisradical states endows them with unique NIR absorption properties, e.g., NIR absorption bands for the mono- A nd bisradical states observed at â1800 and â1450 nm, respectively. These catenanes are potentially useful in applications that include NIR photothermal conversion, UV-vis-NIR multiple-state electrochromic materials, and multiple-state memory devices. Our findings highlight the principle of "mechanical-bond-induced stabilization" as an efficient strategy for designing persistent organic radicals.
ASJC Scopus subject areas
- Colloid and Surface Chemistry