Stable π-Extended Thio[7]helicene-Based Diradical with Predominant Through-Space Spin-Spin Coupling.

Area of Science:

• Organic Chemistry
• Materials Science
• Molecular Physics

Background:

• Helicenes are chiral aromatic compounds with unique electronic properties.
• Stable open-shell diradicals are of interest for molecular magnetism and spintronics.
• Investigating through-space spin-spin coupling (TSC) is crucial for understanding intramolecular magnetic interactions.

Purpose of the Study:

• To synthesize a novel π-extended thiohelicene scaffold capable of hosting stable radicals.
• To characterize the electronic and magnetic properties of the resulting open-shell helical diradical, ET7H-R.
• To explore the phenomenon of through-space spin-spin coupling in a chiral helical system.

Main Methods:

• Multi-step organic synthesis to construct the π-extended thio[7]helicene scaffold.
• Functionalization with bulky phenoxy radicals to create the diradical.
• Variable-temperature continuous-wave electron spin resonance (cw-ESR) spectroscopy.
• Superconducting quantum interference device (SQUID) magnetometry.

Main Results:

• Successful synthesis of a stable, air-stable open-shell helical diradical (ET7H-R) with high diradical character (y0 = 0.998).
• Demonstration of nontrivial π conjugation and persistent chirality in the helical structure.
• Observation of predominant through-space spin-spin coupling between radicals at helical terminals.
• Identification of a singlet ground state with a nearly degenerate triplet state via variable-temperature ESR and SQUID magnetometry.

Conclusions:

• Stable helical diradicaloids are viable platforms for fundamental studies of intramolecular through-space spin-spin coupling.
• The synthesized ET7H-R molecule provides a unique system for investigating spin interactions in chiral environments.
• This work opens avenues for designing novel organic materials with tailored magnetic and electronic properties.