Analysis of the transient EPR signals in the photoexcited triplet state. Application to porphyrin molecules
1974; American Institute of Physics; Volume: 61; Issue: 6 Linguagem: Inglês
10.1063/1.1682302
ISSN1520-9032
Autores Tópico(s)Photodynamic Therapy Research Studies
ResumoAnomalous EPR line intensities observed in the photoexcited triplet state of porphyrins at 100°K are discussed. A kinetic model consisting of the singlet ground state and the first excited triplet state is developed. The EPR signal intensities are expressed in terms of the kinetic rate constants and are given as linear combinations of two exponents. With these expressions the transient effects on the line intensities can be explained. Experimental results for two porphyrin molecules H2TPP (tetraphenyl porphyrin free base) and H2(PF)TPP (pentafluorotetraphenyl porphyrin free base) are presented and compared with the theory. From the analysis we evaluated the spin lattice relaxation rate W, the depopulation rate constants kp and the ratio between the population rate constants Ap: For H2TPP, kx =(6±2)×102 sec−1, ky =(3±1)×102 sec−1, kz =(1.5±0.5)×102 sec−1, Ax:Ay:Az≃1:0.6:0.2, and W =3.3×103 sec−1. For H2(PF)TPP, kx =(5±2)×102 sec−1, ky =(1.4±0.4)×102 sec−1, kz =(1.0±0.3)×102 sec−1, Ax:Ay:Az≃1:0.2:0.3, and W =1.7×104 sec−1.
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