Electronic states and their molecular dynamics in fluid solution by multi-frequency EPR

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The following results were obtained in this research project.1. We succeeded in observations and simulations of the EPR spectra of the excited triplet (T_1) states in fluid solution. The molecules include metalloporphyrins (MTPP : M = Zn, Mg, H_2), phthalocyanines and subphthalocyanine. The processes concerning the Jahn-Teller split state and/or the second excited triplet (T_2) state and in-plane and out-of-plane rotations were separated at various temperatures and the activation energies were obtained in each process.2. The spin-relaxation times of metalloporohyrins were obtained in the T_1 states by multi frequency, X, Q, and W band, EPR techniques. The results that the spin-spin relaxation time remained the same and that the spin-lattice relaxation time varied depending on the band, ex. two orders of magnitude longer in the W band, indicate that theses relaxations are dominated by the spin dipolar mechanism The shorter spin-lattice relaxation time in ZnTPP and MgTPP indicate the proximity of the T_2 state.3. The g values of the excited quartet states were obtained by X band EPR in the T_1-radical systems. The values were different depending on the system and gave rise to the intersystem crossing rate between the excited doublet and quartet states. On the basis of the transient absorption experiments, it turned out that the larger are the J value between T_1 and the radical, the slower the intersystem crossing rates are.4. The EPR spectra of the excited doublet and quartet states and the doublet ground state were separated and assigned for the first time in solution. The time profiles of these states show that the two excited states, the doublet and the quartet, (toy different indicating independent decay processes involving in the excited states.