LUMINESCENCE QUENCHING OF COPPER(II) PORPHYRINS WITH LEWIS-BASES

We report quenching studies of the emissions from Cu(TPP), Cu(TMP), an d Cu(OEP) in toluene where TPP, TMP, and OEP denote the doubly deproto nated forms of tetraphenylporphyrin, tetramesitylporphyrin, and octaet hylporphyrin, respectively. The quenchers are a series of Lewis bases including acetonitrile, DMF, DMSO, three different pyridines, and THF. Results with a sterically encumbered pyridine along with the correlat ion between quenching ability and donor strength prove that formation of a five-coordinate adduct induces the quenching. Small positive enth alpies of activation for quenching suggest that adduct formation is re versible, at least with the weaker donors. We conclude that the quench ing is not intrinsic to the intraligand excited state of the adduct bu t is due to the influence of another excited state. The available evid ence suggests that a d-d state involving z(2) --> x(2) - y(2) excitati on is probably responsible for the quenching.