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 b-pyrrole substituted tetraphenylporphyrins, MTPP(R), MTPP(Br)(2)(R) (where R = -CHQC(CN)(2), -CHQC(CN)(COOC2H5), -CHQ(CN)(COOH) and M = 2H, Ni(II), Cu(II)) and MTPP(NO2)(Ph-p-R')(2) (R' = -CHO and -CHQC(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-CHQ(CN)(2))(2) (10) are highly nonplanar among beta-trisubstituted porphyrins reported to date as evidenced from the mean displacement of beta-pyrrole carbon (DCb) in the range +/-(0.39-0.674)angstrom. 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 degrees) while dicyanovinyl stays aside for NiTPP(NO2)-( Ph-p-CHQ(CN)(2))(2) (dihedral angles relative to the pyrrole NC4-mean plane are 75.031 and 67.471). 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-CHQ(CN)(2))(2) (10) also acts as chemodosimeter for CN- ions but no vivid changes are observed via different spectroscopic methods.