[Quenching of triplet states by Fe(II)- and Fe(III)-porphyrins]

The quenching of triplet states of metalloporphyrin molecules differing in the position of the lowest triplet state (from 9.000 to 15.000 cm-1) by ion complexes of octaethylporphin (OEP) has been investigated. High-spin ferric complex FeCl-OEP in dimethylformamide, toluene and ethanol, low-spin ferric complex FeCl(imidazole)2-OEP in toluene and diamagnetic ferrous complex Fe(piperidine)2-OEP in pyridine-piperidine (25:1) were used as quenchers. It has been found that all iron complexes investigated are effective quenchers of triplet states. The values of bimolecular quenching constants fall within the limits of (1 divided by 4) X 10(9) M-1 sec-1. Energy transfer to low-lying excited levels of iron porphyrins which are due to the presence of 3d electrons of ferric (ferrous) ion has been shown to play an essential role in the quenching process.