Anomalous Metalloporphyrin and Chlorophyll a Activated Chemiluminescence of Dimethyldioxetanone. Chemically Initiated Electron-Exchange Luminescence

Article abstract of DOI:10.1021/ja00543a036

A wide range of fluorescent electron donors catalyze the chemiluminescence of dimethyldioxetanone (1) by the chemically initiated electron-exchange luminescence (CIEEL) pathway.In general, the magnitude of the catalytic rate constant and the efficacy of excited-state generation correlate well with the one-electron oxidation potential of the donor.Exceptions to this correlation are several zinc and magnesium porphyrins, including chlorophyll a, for which their chemiluminescent catalysis is much greater than predicted by their oxidation potentials.The critical role of the central metal atom in eliciting this unusual behavior was evaluated by determining the catalytic rate constants and the initial chemiluminescence intensities of several nonmetalled as well as differently metallated porphyrins.These results suggest that formation of a ground-state complex between 1 and certain metalloporphyrins is the cause of the unusual catalysis.This analysis is supported by studies of the inhibition of the anomalous catalysis by the addition of competitive complexing agents.In addition, spectroscopic evidence of a ground-state complex between zinc tetraphenylporphyrin (ZnTPP) and tetramethyldioxetane, a model for 1, has been obtained.