Axially‐ and <i>Meso</i> ‐Substituted Aza‐Crown‐Ether‐Incorporated B ^III Subporphyrins: Control of Electron‐Donating Ability by Metal Ion Chelation

A series of subporphyrin-based fluorescent probes bearing 1-aza-15-crown-5 or 1-aza-18-crown-6 moieties at the meso axial positions were prepared by Pd-catalyzed Buchwald-Hartwig amination reaction corresponding bromosubporphyrins. Both types aza-crown-ether-incorporated subporphyrins in solution and exhibited cation-dependent absorption fluorescence changes. In titration experiments, opposite responses observed for two subporphyrins. Namely, quenching occurred meso-substituted while enhancement was axially-substituted These results demonstrate advantage being viable to serve as turn-off-type turn-on-type probes, depending upon substitution pattern.