Pulsed EPR measurements on reaction rate constants for addition of photo-generated radicals to double bonds of diethyl fumarate and diethyl maleate

Pulsed EPR Study of the Initial Steps of Radical-Scavenging Reactions of C70 with Diphenylphosphine Oxide, Hydroxycyclohexyl, and 2-Hydroxypropyl Radicals

The radical scavenging reactions of C₇₀ were investigated using time-resolved (TR-) and pulsed electron paramagnetic resonance (EPR) methods. In the diphenylphosphine oxide (DPPO) radical and C₇₀ system, structural isomers of the adduct radicals of C₇₀ appeared in the TR-EPR spectrum with clear hyperfine structures due to the phosphorus atom. Four isomers were identified through the analysis of the hyperfine coupling constants. The assignment of the adduct radicals was confirmed by the semiempirical calculation of the relative addition reaction rate constants that produce each isomer. The radical scavenging rate constants, k_sca, of C₇₀ in toluene were determined for DPPO, hydroxylcyclohexyl, and 2-hydroxypropyl radicals through electron spin echo observations using the pulsed-EPR method. The k_sca values were nearly 10⁹ mol^-1 dm³ s^-1 and were almost equal to the diffusion-controlled rate constant in toluene. This proves that C₇₀ acts as an excellent radical scavenger. In addition, the radical addition rate constants, k_add, of C₇₀ for varying carbon atoms in C₇₀ were obtained by considering the peak intensity ratio of the adduct radicals in the TR-EPR spectrum. In this study, we demonstrated that the large number of carbon atoms in pentagons (five-membered rings) is responsible for the high reactivity of fullerenes.

Recent progress in the electron paramagnetic resonance study of polymers

This review article provides an overview of the contemporary research based on a tailor-made technique to understand the paramagnetic behavior of different polymer classes.