The high-resolution solution structure and dynamics of a cofacially aligned porphyrin-phenylenequinone compound have been determined using H-1 NMR spectroscopy and simulated annealing calculations. Members of this class of pi -stacked assemblies feature a 1,8-naphthyl pillaring motif that enforces sub van der Waals interplanar separations between juxtaposed porphyryl, aromatic bridge, and quinonyl components of the donor-spacer-acceptor compound; this structural motif gives rise to a comprehensive set of structurally significant NOE signatures that can be used as constraints in quantitative structural calculations. Examination of such data using ab initio simulated annealing analytical methods shows that 5-[8'-(4"-[8"'-(2'"',5"'-benzoquinonyl)-1"'-naphthyl]-1"-phenyl)-1'-naphthyl]-10,20-diphenylporphyrin displays an unusual degree of conformational homogeneity in the condensed phase, and represents a rare example where such an analysis determines unequivocally a single unique structure in solution.