Spin dynamic studies on (2,5-dimethyl-DCNQI)2 Li by pulsed ESR

Abstract The electron spin relaxation rates T 1e −1 and T 2e −1 of the radical anion salt (2,5-dimethyl-DCNQI) 2 Li are measured temperature- and angular dependent, respectively, at ν = 9.8 GHz. The temperature dependence can be explained by a smooth transition from motional narrowing to spin exchange. A more pronounced transition at 60 K leads to spin pairing. With further decreasing temperature the correlation time of the spin motion becomes longer to reach at 35 K τ = ω L −1 = 10 −10 s. Below that temperature T 1e −1 becomes smaller than T 2e −1 which increases: at 4.5 K T 1e −1 is 0.67 μs −1 (T 1e = 1500 ns) and T 2e −1 = 15 μ s −1 (T 2e = 67 ns). In the temperature range 300 – 35 K T 1e is shorter than T 2e , which demands an anisotropic fluctuating field with a spectral density: J( ω = ω L ) > J( ω = 0). The angular dependencies of T 1e −1 and T 2e −1 cannot be explained by the symmetry of dipolar spin-spin interaction along the DCNQI stacks and the anisotropy of the g-factor, solely. We have to assume contributions from adjacent stacks, as well.