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Area of Science:

  • Organic Chemistry
  • Materials Science

Background:

  • Localized singlet diradicals are crucial in bond-homolysis chemistry and nonlinear optical materials.
  • Existing singlet diradicals often have short lifetimes, limiting their applications.

Purpose of the Study:

  • To design and synthesize an exceptionally long-lived localized singlet diradical.
  • To investigate the role of macrocyclic structures in stabilizing diradicals and influencing their reactivity.

Main Methods:

  • Employed a novel molecular design strategy involving a macrocycle to kinetically stabilize a singlet diradical.
  • Compared the lifetime of the macrocyclic singlet diradical with a standard non-macrocyclic analogue.
  • Studied the reactivity of the ring-closed compound through spontaneous oxidation.

Main Results:

  • Achieved an extremely long-lived localized singlet diradical with a lifetime of 14 μs at 293 K, two orders of magnitude longer than standard diradicals (≈0.2 μs).
  • The diradical demonstrated persistence below 100 K.
  • Spontaneous oxidation of the corresponding ring-closed compound yielded oxygenated products under ambient conditions.

Conclusions:

  • Macrocyclic structures can significantly enhance the kinetic stability and lifetime of localized singlet diradicals through a "stretch effect."
  • The strained macrocyclic framework increases the reactivity of the corresponding σ-bonded compound.
  • This work opens new avenues for the application of diradicals in chemistry and materials science.