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

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 (ΔCβ) 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.