An insight into the communication between β-olefin/phenyl olefin-mediated acceptors and porphyrin π-system: a way to establish porphyrin based chemodosimeters and chemosensors

Abstract

The synthesis of three new classes of mixed β-pyrrole substituted tetraphenylporphyrins, MTPP(R), MTPP(Br)₂(R) (where R = –CHC(CN)₂, –CHC(CN)(COOC₂H₅), –CH(CN)(COOH) and M = 2H, Ni(II), Cu(II)) and MTPP(NO₂)(Ph-p-R′)₂ (R′ = –CHO and –CHC(CN)₂ and M = 2H, Ni(II), Cu(II)) have been reported. The crystal structures of CuTPP(Br)₂-ECA (7a), NiTPP(NO₂)(Ph-p-CHO)₂ (9) and NiTPP(NO₂)(Ph-p-CH(CN)₂)₂ (10) are highly nonplanar among β-trisubstituted porphyrins reported to date as evidenced from the mean displacement of β-pyrrole carbon (ΔC_β) in the range ±(0.39–0.674) Å. The olefin mediated ethyl cyanoacetate is in plane with the porphyrin core in CuTPP(Br)₂-ECA (the dihedral angle relative to the pyrrole NC₄-mean plane is 39.81°) while dicyanovinyl stays aside for NiTPP(NO₂)(Ph-p-CH(CN)₂)₂ (dihedral angles relative to the pyrrole NC₄-mean plane are 75.03° and 67.47°). NiTPP-MN (2), NiTPP-ECA (3), NiTPP(Br)₂-MN (6) and NiTPP(Br)₂-ECA (7) act as chemodosimeters for toxic CN⁻ ions whereas NiTPP-CAA (4) and NiTPP(Br)₂-CAA (8) act as chemosensors to detect toxic ions such as CN⁻, F⁻ and OAc⁻ depending on the acceptor strength and an obstacle in the conjugation pathway. The dicyanovinyl group in the phenyl olefinic-mediated porphyrin NiTPP(NO₂)(Ph-p-CH(CN)₂)₂ (10) also acts as chemodosimeter for CN⁻ ions but no vivid changes are observed via different spectroscopic methods.