The magnitude of 𝐷 is related to the average interspin distance between the two unpaired electrons of FAAF. A 'back-of-the-envelope' calculation, based on the simplified formula: |𝐷| ≈ 490 nm 3 MHz/⟨𝑟⟩ 3 , predicts an average interspin distance ⟨𝑟⟩ ≈ 1.89 nm. This estimated distance is consistent with the DFT optimised geometry for the gas phase structure of FAAF which has a distance of 1.8964 nm between the centres of the fluorenyl (F) fragments. Extracting ⟨𝑟⟩ in this simplified manner may lead to discrepancies caused by the exchange-type integrals contributing to the 𝐷-value (this is not the exchange interaction, 𝐽 ). . For FAAF, the spectrum was simulated using an 85% triplet component. The spectra were simulated by employing isotropic proton hyperfine couplings and an anisotropic 𝐠-tensor with eigenvalues 𝑔 1 , 𝑔 2 , and 𝑔 3 . The dipolar coupling of the triplet component of FAAF was taken into account via the 𝐷-value. Simulations with anisotropic hyperfine couplings were also attempted, however, the number of parameters is very large and renders the interpretation meaningless. It is clear that the asymmetry of the experimental FID spectra is modelled accurately only by the anisotropy of the 𝐠-tensor.