Oxidation of Electron Donor-Substituted Verdazyls: Building Blocks for Molecular Switches

Species
that can undergo changes in electronic configuration as
a result of an external stimulus such as pH or solvent polarity can
play an important role in sensors, conducting polymers, and molecular
switches. One way to achieve such structures is to couple two redox-active
fragments, where the redox activity of one of them is strongly dependent
upon environment. We report on two new verdazyls, one subsituted with
a di-tert-butyl phenol group and the other with a
dimethylaminophenyl group, that have the potential for such behavior
upon oxidation. Oxidation of both verdazyls with copper­(II) triflate
in acetonitrile gives diamagnetic verdazylium ions characterized by
NMR and UV–vis spectroscopies. Deprotonation of the phenol–verdazylium
results in electron transfer and a switch from a singlet state to
a paramagnetic triplet diradical identified by electron spin resonance.
The dimethylaminoverdazylium 9 has a diamagnetic ground
state, in line with predictions from simple empirical methods and
supported by density functional theory calculations. These results
indicate that verdazyls may complement nitroxides as spin carriers
in the design of organic molecular electronics.