Magnetic Coupling of Two Triplet Phenylnitrene Units Joined Through an Acetylenic or a Di-Acetylenic Linkage

Some polymer radicals have been proposed as potential organic magnetic materials. In order to determine where to place the doublet or triplet centers on the side chains of a conjugated polymer chain, we have studied model dimers, i.e., isomeric bis(nitrenophenyl)acetylenes and diacetylenes. They were generated by photolyses of the corresponding diazides in MTHF at 10 K in an ESR cavity. The m,p′-dinitrenes showed strong fine-structure signals characteristic of quintet states that obeyed Curie law in the range 12–85 K. The m,m′-dinitrenes showed fine-structure signals due to quintet states that had the maximum intensities at 50 and 28 K for the mono- and diacetylenes, respectively. It is concluded that the two triplet centers at the m,p′- and m,m′-positions interact, respectively, ferro- and antiferromagnetically. Efforts directed to the construction of ferromagnetic poly(acetylenes) are briefly discussed.