The conformational structure of 5,15-bis[2-[(anthraquinone-2-sulfonyl)oxy]phenyl]-2,8,12,18-tetra-n-butyl-3,7,13,17-tetramethylporphyrin (I) was investigated by a number of NMR techniques (H-1, (H-1) double resonance, NOESY, NOE difference, C-13 (both proton decoupled and coupled, and DEFT), HSC (H-1-C-13), and COLOC), the double-dipole method of Abraham et al., and semiempirical (MNDO) and force-field (CHARMm) geometry optimizations. In contrast to earlier publications on related systems, it was established that I does not have a fixed geometry but has a dynamical structure instead : the (anthraquinone-2-sulfonyl)oxy side chains are almost completely free to move about, with (probably) a slight preference for a folded conformation. No indications were found for the existence of an energy barrier between the folded and an open conformation. Further, on the basis of NMR NOE measurements and the principle of ring current induced changes in NMR chemical shifts (all NMR experiments showing the presence of large ring current induced changes in the chemical shifts of some of the anthraquinone protons), it is concluded that a molecule of I spends a considerable amount of time in a folded conformation. However, the double-dipole method of Abraham et al, proves to be quite unable to derive sound structural conclusions from our NMR data.