ISSN:
0749-1581
Keywords:
time-resolved EPR
;
liquid crystals
;
CIDEP
;
photoinduced electron transfer
;
porphyrin-crown ether-quinones
;
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Time-resolved EPR spectra are reported for photoexcited porphyrin - quinones with butylene and cis- or trans- cyclohexylene spacers between porphyrin donors and crown ether - quinone acceptors. In the nematic phases of liquid crystals, polarized triplet EPR spectra of the porphyrin moiety could be observed at early delay times (0.1-0.6 μs) after laser flash irradiation. At later delay times (1-2 μs) the triplet EPR spectra of the charge-separated radical pair state, created by intramolecular electron transfer from the porphyrin donor to the crown ether quinone acceptor, could be detected. The similarity of the zero-field splitting parameters D of the cyclohexylene- and butylene-linked compounds shows that the radical pair of the flexible butylene-linked compound is in a stretched conformation. However, longer laser irradiation of the species with the flexible bridge results in the formation of a novel triplet radical pair species with a shorter porphyrin - quinone separation indicating a photoinduced backfolding of the quinone over the porphyrin plane. Comparison of the cis- and trans-cyclohexylene-linked compounds reveals a distortion of the cyclohexylene spacer in the cis compound.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrc.1260331307
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