Abstract
Phylloquinone biradical triplet species were generated by 300 nm irradiation of frozen (77 K) solutions or by treatment with AlCl3. The shape of the (Δms=1) electron paramagnetic resonance (EPR) signal of the triplet is axially symmetric (E=0) with D=19±0.5 mT for photo-induced and D=11.2±0.5 mT for chemically induced radicals. A half-field signal (Δms=2) in the region of g≈4 was detected in both cases, confirming its assignment as a triplet. An additional line arising at the center of the (Δms=1) signal with g=2.0048±0.0002 was assigned to the phylloquinone radical anion (PhQ•-). Electron nuclear double resonance (ENDOR) measurements of the triplet revealed the sign of the D parameter. For photo-generated radicals it appeared to be negative, which is the characteristic of radical dimers with well-separated partners (biradicals). Spin-spin distances of 5.3 and 6.3 Å, respectively, were estimated from the D parameter of photo-generated and chemically prepared phylloquinone biradicals.
Original language | English (US) |
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Pages (from-to) | 255-260 |
Number of pages | 6 |
Journal | Journal of Photochemistry and Photobiology A: Chemistry |
Volume | 161 |
Issue number | 2-3 |
DOIs | |
State | Published - Jan 30 2004 |
Externally published | Yes |
Keywords
- Biradicals
- Electron nuclear double resonance
- Electron paramagnetic resonance
- Electron transfer
- Phylloquinone
ASJC Scopus subject areas
- Chemistry(all)
- Chemical Engineering(all)
- Physics and Astronomy(all)