Electron‐spin resonance (ESR) characterization of quintet spin‐state bis‐nitroxide‐bearing cyclopentane‐1,3‐diyl diradicals

High‐spin organic molecules have attracted much attention as spin sources for magnetic materials . In this paper, a novel high‐spin organic molecule was designed according to a logical strategy. A 2,2‐dimethylcyclopentane‐1,3‐diyl diradical unit was utilized as a spin source and a spin‐bridged fragment. In addition, nitroxides were introduced as spin sources. Quintet electron‐spin resonance (ESR) signals, which were attributed to the 1,3‐di(3′‐nitoroxyphenyl)‐2,2‐dimethylcyclopentane‐1,3‐diyl tetraradical ( TR ), were observed in a 2‐methyltetrahydrofuran glassy matrix at 80 K after the photodenitrogenation of a newly synthesized azoalkanes AZ . A simulation of the signal provided the zero‐field splitting parameters D (| D |/hc = 0.0127 cm −1) and E (| E |/hc = 0.0014 cm −1 ) for the quintet state of the tetraradical TR . The parameter D of the quintet state of TR was found similar to those of the previously reported quintet spin states of tetraradical TR1 with two cyclobutane‐1,3‐diyl units (0.0190 cm −1 ) and TR2 with two 2,2‐dimethylcyclopentane‐1,3‐diyl diradicals (0.0116 cm −1 ). Copyright © 2014 John Wiley & Sons, Ltd.