Stable π-Extended Thio[7]helicene-Based Diradical with Predominant Through-Space Spin–Spin Coupling
Hao Wu, Hiroki Hanayama, Max Coehlo, Yanwei Gu, Zehua Wu, Satoshi Takebayashi, G. Jakob, Serhii Vasylevskyi, Dieter Schollmeyer, Mathias Kläui, Grégory Pieters, Martin Baumgarten, Kläus Müllen, Akimitsu Narita, Zijie Qiu
Abstract
In this work, a novel π-extended thio[7]helicene scaffold was synthesized, where the α-position of the thiophene unit could be functionalized with bulky phenoxy radicals after considerable synthetic attempts. This open-shell helical diradical, ET7H-R, possesses high stability in the air, nontrivial π conjugation, persistent chirality, and a high diradical character ( y 0 of 0.998). The key feature is a predominant through-space spin–spin coupling (TSC) between two radicals at the helical terminals. Variable-temperature continuous-wave electron spin resonance (cw-ESR) and superconducting quantum interference device (SQUID) magnetometry in the solid state reveal a singlet ground state with a nearly degenerate triplet state of ET7H-R . These results highlight the significance of a stable helical diradicaloid as a promising platform for investigating intramolecular TSCs.