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Kinetic Study of the Photoexcited Triplet State of Free Base Porphyrins by EPR
Author(s) -
Scherz A.,
Orbach N.,
Leva H.
Publication year - 1974
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.197400099
Subject(s) - chemistry , electron paramagnetic resonance , porphyrin , free base , tetra , reaction rate constant , triplet state , crystallography , resonance (particle physics) , zero field splitting , population , analytical chemistry (journal) , nuclear magnetic resonance , photochemistry , atomic physics , kinetics , electron , medicinal chemistry , molecule , spin polarization , salt (chemistry) , physics , demography , quantum mechanics , organic chemistry , sociology , chromatography
An electron paramagnetic resonance (EPR) study of the photoexcited triplet state of four free base porphyrins is presented. The zero field splitting parameters (ZFS) |D| and |E| were calculated from the EPR spectra of the porphyrins dissolved in n‐octane matrices at 80°K. |D| = 0.0359 cm −1 , |E| = 0.0079 cm −1 for tetra phenyl porphyrin (H 2 TPP), |D| = 0.0432 cm −1 , |E| = 0.0037 cm −1 for tetra (per‐fluoro) phenyl porphyrin H 2 T (per‐F) PP, |D| = 0.0366 cm −1 , |E| = 0.0078 cm −1 for tetra (para‐chloro) phenyl porphyrin H 2 T(P‐Cl)PP, |D| = 0.0369 cm −1 , |E| = 0.0076 cm −1 for tetra (para‐methyl) phenyl porphyrin H 2 T(P‐Me)PP. The transient behavior of the EPR signal intensities in the last two porphyrins is discussed. The depopulation rate constants of the triplet sublevels k p , the ratio between the population rate constants A p (at zero field, p = x,y,z), and the spin lattice relaxation rate W within the triplet manifold, were calculated. k x = (12 ± 2) × 10 2 sec −1 , k y = (0.5 ± 0.1) × 10 2 sec −1 , k z = (1.2 ± 0.4) × 10 2 sec −1 , A x :A y :A z ≃ 0.63:0.01:0.33, W = (0.4 ± 0.1) × 10 4 sec −1 for H 2 T(P‐Cl)PP, k x = (7 ± 2) × 10 2 sec −1 , k y = (4 ± 1) × 10 2 sec −1 , k z = (1.5 ± 0.5) × 10 2 sec −1 , A x :A y :A z ≃ 0.56:0.31:0.13, W = (1.7 ± 0.4) × 10 3 sec −1 for H 2 T(P‐Me)PP.