Structure and dynamics of radicalized hydrocarbon derivatives included in perhydrotriphenylene single crystals

Abstract

The radical obtained by γ-irradiation of the nonadecan-10-one/perhydrotriphenylene (10-NDO/PHTP) inclusion compound has been studied by EPR spectroscopy. The radical is formed by removal of one of the protons in the α position to the carbonyl group and the unpaired electron spin is coupled to the α proton and to two equivalent β protons. The hyperfine (hf) coupling constants vary slowly on lowering the temperature until an abrupt change occurs at T = 150 K. The radical reorients quickly on the EPR timescale inside the PHTP channels. The reorientational correlation time τ_r is obtained from the linewidth values and it is found to be shorter than the τ_r value measured previously for the same radical included in urea. The EPR spectrum changes in the timescale of weeks and after two months displays the presence of an additional hf coupling with a pair of equivalent protons, the other spectral parameters being unchanged with respect to those of the freshly irradiated radical. This modification is probably due to a folding of the radicalized guest molecule inside the host channel.