The Effects of Conjugation Path Variation on Electron Delocalization in Phenoxyl-Based Systems.Author(s): Yanbing Liu | Paul M. Lahti
Journal: Molecules ISSN 1420-3049
Volume: 9; Issue: 9; Start page: 725; Date: 2004;
Keywords: 2 | 6-Di-tert-butylphenoxyl | conjugated polyradicals | spin delocalization | exchange | molecular magnetism | electron spin resonance | hyperfine coupling.
A number of persistent 2,6-di-tert-butylphenoxyl based radicals were synthesized as models for unpaired spin delocalization as a function of conjugation pathway, and were investigated by ESR and UV-vis spectroscopy. Phenoxyl spin delocalizes significantly onto a para-phenyl ring, but further delocalization through a meta-vinyl or meta-carbonyl linkage is not detectable by ESR hyperfine coupling. UV- vis spectra do show a red shift of the longest wavelength transition for a carbonyl-type substituent by comparison to a vinyl substituent in the meta-position of a para-phenyl group. By comparison, a para-styryl substituent on the phenoxyl causes very large spin delocalization from the phenoxyl unit, with the largest hyperfine coupling being found on the ethenyl unit of the assemblage. This large delocalization accounts for the reactivity of radicals that incorporate such units.