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The photoexcited triplet states of chlorophyll à and b are studied by the EPR method at ≈85 K using modulated light excitation. Both compounds show anomalous EPR line intensities and transient kinetics, indicating electron spin polarization (ESP) in the photoexcited triplet state. EPR studies, using Mg-tetraphenyl porphyrin (MgTPP) dissolved in n-octane show that ESP occurs also in that solvent. It is shown that the zero field splitting (ZFS) parameters of MgTPP depend strongly on the solvent. From the analysis of the data for chlorophyll a and b we evaluate: (1) the population rate constants (kp); (2) the ratio between the population rate constants (Ap) (p = x, y, z) and, (3) the spin lattice relaxation rate W. In both chlorophylls the in-plane component, x, is predominantly populated and depopulated. The ZFS parameters have been also determined for the above compounds. 相似文献
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V. I. Sokolov A. F. Pozharskii I. S. Kashparov A. G. Ivanov B. I. Ardashev‡ 《Chemistry of Heterocyclic Compounds》1974,10(4):485-488
2,3-Dihydro derivatives of perimidine were obtained in high yields by the action of lithium aluminum hydride or sodium borohydride on perimidinium salts and 1,3-dialkylperimidones. 相似文献
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Electron spin polarization in the photoexcited triplet state of tetraphenyl porphyrin was detected at 100°K using EPR technique. The zero field splitting parameters |D| and |E| the free base porphyrin were found to be 0.0369 ± 0.0005 and 0.0082 ± 0.0005 cm?1, respectively. 相似文献
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Novel mechanisms of the electron spin polarization were reported. Effect of spin-selective interactions within the photo-excited preexisting molecular dimers was utilized. Processes occurring within dimers and upon escape from the dimer cage were considered. 相似文献
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In this work we study a reaction–diffusion problem with delay and we make an analysis of the stability of solutions by means of bifurcation theory. We take the delay constant as a parameter. Special conditions on the vector field assure existence of a spatially nonconstant positive equilibrium Uk , which is stable for small values of the delay. An increase of the delay destabilizes the equilibrium of Uk and leads to super or subcritical Hopf bifurcation. 相似文献
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Formation and protonation of aromatic anion radicals in 2-propanol were studied by kinetic spectrophotometric pulse radiolysis. All polycyclic hydrocarbons studied were found to react very rapidly with e?solv. Those with relatively high electron affinity were also reduced by (CH3)2CO?. The anion radicals formed undergo protonation by direct reaction with the alcohol molecule. The rate constants for this protonation vary from ≈ 6 × 105 s?1 for cis-stilbene and naphthalene down to 20 s?1 for perylene. The variations in rates are discussed in terms of changes in singlet energy separation (ΔES1 ← S0). The logarithm of the protonation rate constant for alternant hydrocarbons is linearly dependent on ΔES1 ← S0. 相似文献