Amino Acid-Porphyrin Conjugates: Synthesis and Study of their Photophysical and Metal Ion Recognition Properties.

Synthesis, photophysical and metal ion recognition properties of a series of amino acid-linked free-base and Zn-porphyrin derivatives (5-9) are reported. These porphyrin derivatives showed favorable photophysical properties including high molar extinction coefficients (>1 × 10(5) m(-1) cm(-1) for the Soret band), quantum yields of triplet excited states (63-94%) and singlet oxygen generation efficiencies (59-91%). Particularly, the Zn-porphyrin derivatives, 6 and 9 showed higher molar extinction coefficients, decreased fluorescence quantum yields, and higher triplet and singlet oxygen quantum yields compared to the corresponding free-base porphyrin derivatives. Further, the study of their interactions with various metal ions indicated that the proline-conjugated Zn-porphyrins (6 and 9) showed high selectivity toward Cu(2+) ions and signaled the recognition through changes in fluorescence intensity. Our results provide insights on the role of nature of amino acid and metallation in the design of the porphyrin systems for application as probes and sensitizers.