X- and W-band time-resolved electron paramagnetic resonance studies on radical-excited triplet pairs between metalloporphyrins and axial-ligating nitroxide radicals

Jun Ichi Fujisawa, Kazuyuki Ishii, Yasunori Ohba, Seigo Yamauchi, Michael Fuhs, Klaus Möbius

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59 Citations (Scopus)

Abstract

A chemically induced dynamic electron spin polarization (CIDEP) study has been accomplished on radical-excited triplet pairs (RTP) in systems of metalloporphyrins, MgTPP, ZnTPP, and ZnOEP, and pyridinesubstituted nitronyl nitroxide radicals, nit-R (R = o-py, m-py, and p-py), by X- (9.5 GHz) and W-band (95 GHz) time-resolved electron paramagnetic resonance (TREPR) in solution. Axial-ligations between the porphyrins and the radicals were ascertained from visible absorption spectra except for the nit-o-py system. The TREPR spectra were composed of two signals, which were assigned to those of the ground (D0) state of the radical and the excited quartet (Q1) state of the RTP. These components showed two kinds of CIDEPs in different time regions. The polarizations of the Q1 state were attributed to radical-triplet pair mechanisms (RTPMs) with singlet and triplet precursors. In the nit-p-py and the nit-m-py systems, the polarizations of the radical were generated via an electron spin polarization transfer (ESPT) from the Q1 state and the RTPM. The CIDEPs observed for the nit-o-py system were interpreted by ESPT and RTPM with the excited triplet (T1) porphyrin. From the analysis of the RTPM polarizations, an exchange interaction between the T1 porphyrin and the radical was found to be ferromagnetic for the nit-p-py system and antiferromagnetic for the nit-m-py and the nit-o-py systems.

Original languageEnglish
Pages (from-to)5869-5876
Number of pages8
JournalJournal of Physical Chemistry A
Volume101
Issue number33
DOIs
Publication statusPublished - 1997 Aug 14

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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