Luminescence spectra, excitation spectra, and lifetimes taken on Cu and VO porphyrins in polymethylmethacrylate on a Cryohyphen;Tip between 80 and 10deg;K confirm the prediction that the unpaired metaldelectron couples with the porphyrin triplet to give ldquo;tripdoubletrdquo; and quartet states. Four Cu porphyrins show loss of the main shorthyphen;wavelength luminescence peak and a lifetime increase from sim;thinsp;100 to sim;thinsp;1000mgr;sec over the temperature range 80ndash;10deg;K that is consistent with a change from tripdoublet to quartet luminescence. CuTPP and VOEtio show no spectral change, but similar lifetime increases for CuTPP around 80deg;K and for VOEtio around 15deg;K suggest that luminescence from the former is quartet at all temperatures studied and from the latter tripdoublet. VOTPP gives anomalously short lifetimes between 8 and 16mgr;sec. Nonexponential decay is observed in all cases but VOTPP, and is attributed to slow spinndash;lattice relaxation among the quartet sublevels.
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