oscillations in "long-field" molecules compared with "round-field" molecule^^^^^^ may favor internal conversion. Should data on aromatic hydrocarbons embodying these geometries (coronene vs. perylene, for example) bear out this expectation, some clue will be afforded toward the understanding of internal conversion in complex molecules.Complexes of TPP and Transition Metals.-Entirely negative results were obtained in attempts to observe triplet states of copper and cobalt TPP complexes by flash-excitation. Even in the region adjoining the Soret band, and with oscillograms taken under very favorable scattered light conditions; no change in absorption was observed. Assuming the triplet absorption to be comparable to that of TPP or ZnTPP, a 5y0 conversion lasting 1 x A very short-lived phosphorescence and no observable fluorescence was iound by Becker and KashaIg in nickel and copper porphyrins in rigid EPA (ether-isopentane-alcohol) , compared with strong fluorescence and weak phosphorescence in non-paramagnetic complexes. This was attributed to enhancement of spin-orbit interactions by the paramagnetic ionz0 which both increased the yield of triplet by radiationless transition from the excited singlet and shortened the lifetime for radia-
3.second would have been detected readily.
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