1D and 2D FT-EPR Studies on the Photoinduced Electron Transfer Reaction from Zn Porphyrin to Duroquinone in CTAC Micellar Solution

Abstract

Abstract A photoinduced electron transfer reaction in a model system of the photosynthesis was investigated by means of pulsed EPR in one (1D)- and two-dimensions (2D). EPR spectra of a spin correlated radical ion pair(SCRP) and a spin polarized radical anion were observed in the system of tetrakis(4-sulfonatophenyl) porphyrinozinc(II) (ZnTPPS)/duroquinone (DQ)/cetyltrimethylammonium chloride micellar solution. In order to investigate the dynamics and structures of the intermediate species, a non-linear least square fitting (NLLSQ), instead of linear prediction (LP), was examined for analyses of free induction decays (FID’s) in a 1D experiment. FID’s were fairly well reproduced with the NLLSQ method as a sum of the signals of the DQ anion and the SCRP. For the DQ anion, the linewidth gradually decreased indicating movement of the anion across the micelle/water interface. For a definitive assignment of the SCRP, a 2D nutation experiment was performed. Different flip angle dependences were observed for the SCRP and the free anion. Under an assumption of an average exchange interaction (J), the 2D spectra of the SCRP were simulated, including an off-resonance effect on the basis of density matrix formalism. Comparison of the calculated and observed spectra indicated that the upper limit of the average |J| was 0.3 MHz (J < 0).