Transient EPR studies of ion-paired metalloporphyrin heterodimers
Journal Article
·
· Journal of Physical Chemistry
- Freie Universitaet Berlin (Germany)
- Brandeis Univ., Waltham, MA (United States)
- Hungarian Academy of Sciences, Budapest (Hungary)
- Hebrew Univ. of Jerusalem (Israel)
Spin-polarized transient EPR spectra measured at 9 GHz (X-band) and 24 GHz (K-band) are observed for the metalloporphyrin heterodimers formed by MTTAP (metal/free base meso-tetrakis[4-trimethylanilinium]-porphyrin, M = Zn, Mg or H{sub 2}) and CuTSPP (copper meso-tetrakis[p-sulfonatophenyl]porphyrin). In the temperature range 5-120 K, the EPR transients obtained following pulsed light excitation at 532 nm show a strong temperature dependence. The dimers exhibit two distinct types of EPR signals which may be separated on the basis of their different decay kinetics. The spectrum of one of the signals can be assigned to a triplet state of the dimers, whereas the other spin-polarized spectrum clearly shows involvement of the Cu(II) metal ion. This spectrum is tentatively assigned to the doublet ground state of the CuTSPP moiety in the dimers. It is proposed that the observed spin polarization is generated by a radical triplet pair mechanism (RTPM). In ZnTTAP-CuTSPP and H{sub 2}TTAP-CuTSPP both spectra are observed, whereas only the latter spectrum is obtained in MgTTAP-CuTSPP. In ZnTTAP-CuTSPP, the triplet-state spectrum shows only small but significant differences from that of the isolated ZnTTAP monomer, indicating that the triplet state is localized on the ZnTTAP component of the dimer. 18 refs., 5 figs., 1 tab.
- OSTI ID:
- 196643
- Journal Information:
- Journal of Physical Chemistry, Journal Name: Journal of Physical Chemistry Journal Issue: 2 Vol. 100; ISSN JPCHAX; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
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