DELOCALIZATION OF UNPAIRED ELECTRONS IN ACCEPTOR-BRIDGE-DONOR MOLECULAR-STRUCTURES AS MONITORED BY CW-EPR SPECTROSCOPY

This paper reports the application of EPR spectroscopy to study the sp in density distribution of unpaired electrons in acceptor-hydrogen bri dge-donor molecular complexes created by irradiation of the organic mo lecule piperidine with different substitutional acid groups. 9 GHz CW- EPR measurements were made at 290 K on polycrystalline samples which w ere gamma-irradiated with a 170 kGy dose. Measurements were also made on UV-irradiated frozen methanol solutions at 77 K. It was concluded t hat the ionizing radiation generates the ion radical by the removal of one hydrogen atom from the piperidine ring and that significant deloc alization of the unpaired electron occurs on this ring. It was found t hat increasing the electronegativity of the hydrogen bridge causes a s ignificant increase in the nitrogen hyperfine interaction and the obse rvation of an additional hyperfine splitting which implies that a sign ificant change in the spin density distribution of the unpaired electr on has occurred. Measurements were also made on irradiated stilbene to study a pi-bridge molecular structure. It was found that the ionizing radiation generates the radical by the addition of one hydrogen atom to a phenyl ring and that significant delocalization of the unpaired e lectron occurs on the pi-bridge connecting the two phenyl rings and on one of these rings.