Bis(aryloxy)phosphine azides (BAPAs) were prepared from corresponding phenols. The synthesis of BAPAs was limited to sterically hindered aryloxy moieties. Photolysis of the BAPAs under a variety of conditions yielded phenoxyl radicals. During photolysis of BAPAs in the solid state at cryogenic temperatures, triplet state radical pairs were observed by EPR spectroscopy. Studies were carried out to determine the identity of these radical pairs. In most cases the radical pairs obtained consisted of the corresponding aryloxy groups in the BAPA being studied. Co-crystallization of bis(2,6-di-t-butyl-4-methoxyphenoxyl)phosphine azide with 2,6-di-t-butyl-4-methoxyphenol resulted in solid state reactions between the 2,6-di-t-butyl-4-methoxyphenoxyl radicals generated upon photolysis and the host matrix at cryogenic temperatures. This resulted in new radical pairs whose identity was determined by EPR spectroscopy. Annealing photolyzed samples of BAPAs caused only slight changes in the zero field splitting parameters (zfs). Photolysis of BAPAs in potassium chloride matrices was developed as a new method for the analysis of radical pairs in the solid state. Curie law studies on the radical pair formed between two 2,6-di-t-butyl-4-methoxyphenoxyl radicals indicates that the radical pair may be a ground state triplet.
Three conformationally inflexible dinitrenes, 1,8-dinitrenoanthracene, 2,6-dinitrenodibenzofuran and 2,6-dinitrenobiphenylene were prepared as tests for the spin dipolar model. The spin dipolar model predicts that the zfs parameters in a quintet state molecule comprised of two triplet subunits will depend on the vector interaction angle between the triplet subunits. In order to test the spin dipolar model unambiguously, conformationally rigid dinitrenes with unusual vector interaction angles were prepared. In each case, a quintet state spectrum was observed which was well simulated using the eigenfield EPR simulation method. The zfs parameters extracted from the EPR spectra closely matched those predicted by the spin dipolar model. These results appear to prove that the spin dipolar model may be quantitatively as well as qualitatively correct. Curie law analyses of the dinitrenes indicated that all three were ground state quintets.
