Luminescence of porphyrins and metalloporphyrins. Part 2.—Copper(II), chromium(III), manganese(III), iron(II) and iron(III) porphyrins

Abstract

The absorption spectra of paramagnetic transition metal porphyrins consist of (ππ*), charge-transfer and tripmultiplet transitions. The tripmultiplet states result from interaction between the metal d-orbitals and the porphyrin (ππ*) excited triplet states. For Cu^IITPP, luminescence occurs from the lowest energy tripquartet state whilst Cr^IIITPP shows luminescence from tripquartet and tripsextet states. Luminescence from Mn^IIITPP and Fe^IIITPP is much less efficient and originates from the second tripmultiplet state. The rate constants for deactivation of the tripmultiplet states depend markedly upon the nature of the central metal ion and are much faster for Mn^III and Fe^III than for Cu^II and Cr^III. Luminescence was not observed for Fe^IITPP, possibly due to the presence of a low-lying c.t. state.