Colorimetric anion sensing by porphyrin-based anion receptors

Porphyrin derivatives 1–4 with H-bond donors and/or color-reporting chromophoric unit were synthesized and studied as anion-binding receptors. 1 and 2 exhibited binding selectivity in the order of AcO−>H2PO4−≫Cl−, Br−, I− in DMSO-d6. Color change tests with several different anions for colorimetric anion sensors (3 and 4) resulted in selectivities for F−, AcO− and H2PO4− in organic solution. While 1 and 2 exhibited good selectivities for AcO− and H2PO4−, 3 and 4 showed a dramatic color change for F− due to increased interaction with a nitrophenylazo phenolic OH group.