Luminescence of porphyrins and metalloporphyrins. Part 10.—Mixed-metal dimers

Abstract

Attaching a second metalloporphyrin to a zinc(II) porphyrin via a short flexible chain results in quenching of both excited singlet and triplet states of the Zn^II porphyrin. The extent of quenching depends markedly upon the nature of the central metal ion contained within the second porphyrin ring (Mn^III≈ Fe^III > Cu^II≫ Ni^II) and upon the site of attachment of the linkage. This latter effect is connected with the influence of the linkage upon the average conformations present in solution since only cofacial arrangements results in efficient quenching. The mode of quenching includes spin–orbit coupling perturbations associated with heavy and/or paramagnetic metal ions as well as energy and electron transfer mechanisms.