High-resolution structure and conformational dynamics of rigid, cofaciallyaligned porphyrin-bridge-quinone systems as determined by NMR spectroscopyand ab initio simulated annealing calculations

The high-resolution solution structure and dynamics of a cofacially aligned porphyrin-phenylenequinone compound have been determined using H-1 NMR spe ctroscopy and simulated annealing calculations. Members of this class of pi -stacked assemblies feature a 1,8-naphthyl pillaring motif that enforces s ub van der Waals interplanar separations between juxtaposed porphyryl, arom atic bridge, and quinonyl components of the donor-spacer-acceptor compound; this structural motif gives rise to a comprehensive set of structurally si gnificant NOE signatures that can be used as constraints in quantitative st ructural calculations. Examination of such data using ab initio simulated a nnealing analytical methods shows that 5-[8'-(4"-[8"'-(2'"',5"'-benzoquinon yl)-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.