Phenol-substituted tetrapyrazinoporphyrazines: pH-dependent fluorescence in basic media.

Tetrapyrazinoporphyrazines (TPyzPzs) bearing one, two, four or eight 3,5-di(tert-butyl)-4-hydroxyphenol moieties were synthesized as zinc(II) complexes and metal-free derivatives. The deprotonation of the phenol using tetrabutylammonium hydroxide induced the formation of a strong donor for intramolecular charge transfer that switched OFF the red fluorescence (λF ∼660 nm) of the parent zinc TPyzPzs. The changes were fully reversible for TPyzPzs with one to four phenolic moieties, and an irreversible modification was observed for TPyzPzs substituted with eight phenols. The sensors were anchored to lipophilic particles in water, and a pKa approximately 12.5-12.7 was determined for the phenolic hydroxyl based on fluorescence changes in different buffers. In addition, a novel concept for fluorescence OFF-ON-OFF switching in metal-free TPyzPzs bearing phenolic moieties upon addition of specific amounts of base was demonstrated.