3,5-di-tert-butyl-3′-(N-tert-butyl-N-aminoxy)-4-oxybiphenyl:: A heterospin diradical with temperature dependent behavior

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 degrees C. In the W-vis spectrum, the diradical showed reversible thermochromic behavior in the -10 to 50 OC 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 degrees 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.