The title diradical was synthesized and investigated by ESR and UV−vis spectroscopy. It was found
to have a lifetime of weeks even in the presence of oxygen, and even survives brief heating in
toluene up to about 60 °C. In the UV−vis spectrum, the diradical showed reversible thermochromic
behavior in the −10 to 50 °C range. In the ESR spectrum, hyperfine analysis showed nearly isolated
behavior by the phenoxyl and nitroxide spin carrying units. Upon warming, additional, broad lines
appeared at the expense of the lower temperature lines. This temperature behavior was reversible
over the 0 to 50 °C range, so long as the raised temperatures were not maintained for long time
periods. The spectral behavior is interpreted as being due to temperature-dependent conformational
effects on the exchange coupling between the spin carrying units, i.e., J-modulated exchange
behavior.