Fig. 6. (a) Crystal structure of cyclo-FF¹⁵ with perpendicular and parallel π–π interactions highlighted in green and red, respectively. (b and c) Close-up of perpendicular (b) and parallel (c) π-stacking. The highlighted distances can be probed by the 2D experiments presented in this paper. Note that the relevant carbon atoms and distances are highlighted for illustrational purposes on the same pair of cyclo-FF molecules. However in a sample at NA, it is highly unlikely to have four ¹³C isotopes occurring in only two cyclo-FF molecules. The highlighted distances contribute individually to the polarization transfer in different molecule pairs across the sample.