Spin-carrying benzoquinone derivatives.

Several 1,4-benzoquinone derivatives carrying oxy-TEMPO radical(s) at the 2-position or 2,5-positions were found to give black crystals by recrystallization from pale yellow solutions and it was revealed from their crystal structures that unusual single-component CT complexes were formed, in which a nitroxide moiety plays the roll of a donor part and a 1,4-benzoquinone group of the same molecule works as an acceptor part, respectively. On the contrary, no CT formation was found for the derivatives carrying oxy-TEMPO radicals at 2,6-positions and one of the TEMPO groups contributes to a CT formation in a 1,4-benzoquinone derivative carrying amino-TEMPO radicals at 2,5-positions derived from fluoranil, while the other one has a close oxygen-to-oxygen contact with another neighboring molecule to give a very large exchange coupling of J/k(B) = -154 K.