Triplet state of metalloporphyrins

Taking advantage of the fact that the triplet state of metalloporphyrins with tetrabenzopor-phyrin (H2TBP or H2I, fig. 10) lies around 12 500 cm-1, a team from Minsk succeeded in sensitizing Ybm luminescence in solutions of [Yb(TBP)L], where L = Cl or acac (acetyl-acetonate), in several solvents like benzene, dimethylformamide (dmf), pyridine, quinoline or a mixture of octane and benzene (Kachura et al., 1974). Energy transfer from the porphyrin chromophore was ascertained by the excitation spectrum of the Ybm luminescence being identical to the absorption spectrum of the complex. In benzene, the quantum yield of... 

There is, of course, the possibility that the low-spin near infra-red absorption is due to a d—d transition. This could be spin-allowed, and may well attain a molar extinction coefficient of 102. However, d—d bands in low-spin ferric haemoproteins are expected to appear at rather higher energies (93) except for d—d transitions between the split orbitals, which are likely to be of very low energy and further into the infra-red. The possibility that the near infra-red absorption of both high-and low-spin systems could be entirely due to n—n triplets can be ruled out, since these are likely to be very much weaker, and the triplet states of metalloporphyrins observed in emission (109) are at rather higher energies (13—15 kK). 

Solvent reorganization energy Internal reorganization energy Photoexcited triplet state of metalloporphyrin Nuclear frequency factor... 

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See also in sourсe #XX -- [ ]

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