Identification of radiation-induced radical structure in azocalix[4]arene: an EPR study.

A macrocyclic azocalix[4]arene (1) based ester derivative was synthesized. The single crystals of azocalix[4]arene were produced by slow evaporation of concentrated ethyl acetate solutions. These single crystals were exposed to (60) Co gamma rays with a dose rate of 0.980 kGy h(-1) for 48 and 72 h to produce a stable free radical. Electron paramagnetic resonance (EPR) measurements were performed in three mutually perpendicular planes of the single crystal in the magnetic field, in addition, temperature dependence of the EPR signal was studied between 120 K and 450 K. The spectra were found to be temperature and angular dependent. Analysis based on the spectra recorded showed that a free radical was formed by fission of a C-H bond. This radical is described as (•) Ca HCb H3 The averages of the principal values of the hyperfine parameters and g-factor are: g = 2.0034, AHa  = 1.28 mT, AH1=H2  = 1.00 mT, and AH3  = 0.49 mT.