Self-complementary double-stranded porphyrin arrays assembled from an alternating pyridyl-porphyrin sequence

Oligomeric porphyrin arrays with an alternating pyridyl-porphyrin sequence were synthesized to explore double-strand formation through self-complementary pyridyl-to-zinc axial coordination bonds. Competitive titration experiments revealed the thermodynamic aspects involved in the zipper effect within double-strand formation. Multiple axial coordination bonds defined the stacked conformation, despite a marginal contribution to the stability of the double-strands. Thus, the zipper cooperativity was the dominant factor for the remarkable stability. Moreover, the dimeric and trimeric porphyrin arrays were independently assembled into double-strands by self-sorting from a binary mixture. Double-strand formation engineered discretely stacked π-systems. Successive slipped-cofacial stacks of the porphyrin rings progressively extended the π-system via exciton coupling over the double-strand while keeping a relatively high fluorescence quantum yield.