Effect of substitution on the redox behaviour and EPR spectra of zinc(II) substituted tetraphenylporphyrin cation radicals

Substituted tetraphenylporphyrinatozinc(II) complexes have been synthesized and characterized by various physicochemical techniques. The effects of su bstitution and counterions on the redox behaviour and EPR spectra have been examined. The EPR spectra revealed that chemical oxidation with bromine yi elds ZnT(X-P)P+Br- (species I) and a brominated tetraphenylporphyrin cation radical (species II). The former exhibits a labile electronic ground state (with (2)A(2u) ground state transforming into (2)A(1u) at 175 K), while th e latter is characterized by a (2)A(1u) state. The lability in the electron ic ground state for species I is discussed in terms of the change in molecu lar geometry as the temperature is lowered. The EPR spectra also revealed f or the first time the formation of dimeric agglomerates of TPP cation radic als in low concentration below the electronic transition (i.e. near 170 K) wherein the paramagnetic sites are antiferromagnetically coupled. Copyright (C) 2000 John Wiley & Sons, Ltd.