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Probing electronic communication in stable benzene-bridged verdazyl diradicals

TitleProbing electronic communication in stable benzene-bridged verdazyl diradicals
Publication TypeJournal Article
Year of Publication2007
AuthorsGilroy, JB, McKinnon, SDJ, Kennepohl, P, Zsombor, MS, Ferguson, MJ, Thompson, LK, Hicks, RG
JournalJ. Org. Chem.
Volume72
Pagination8062–8069
ISSN0022-3263
KeywordsEPR
Abstract

\{[\}GRAPHICS] Two benzene-bridged NN'-bis(isopropyl)6-oxoverdazyl diradicals 7a (1,4-benzene-bridged) and 7b (1,3-benzene-bridged) were prepared and studied by an array of physicochemical techniques aimed at elucidating the intramolecular electronic and magnetic coupling between verdazyl chromophores. The very high stability of these diradicals permits comprehensive investigations of their properties for the first time. The UV-vis spectra suggest negligible direct conjugative overlap involving the radical SOMOs, although significant differences in higher energy absorptions suggest that radical orbitals other than the SOMO are likely communicating via the central p-phenylene bridge in 7a. The electrochemical features of the two diradicals are nearly identical; in each derivative, both radicals are oxidized essentially independently while the reductions occur in a stepwise manner with differences of similar to 100mV between the two reductions. EPR and magnetic susceptibility collectively indicate that the para-bridged diradical is weakly antiferromagnetically coupled while the meta analogue is weakly ferromagnetically coupled, in accord with the topology of the substitution pattern on the central benzene ring.

DOI10.1021/jo7014449