NMR relaxation studies in doped poly-3-methylthiophene

Abstract

Abstract:NMR relaxation rates (1/T1), magnetic susceptibility, and electrical conductivity studies in doped poly-3-methylthiophene (p3MT) are reported in this study. The magnetic susceptibility data show the contributions from both Pauli and Curie spins, with the size of the Pauli term depending strongly on the doping level. Proton and Fluorine NMR relaxation rate has been studied as a function of temperature (3-300 K) and field (for protons at 0.9 T, 9.0 T, 16.4 T, 23.4 T and for fluorine 9.0 T). The temperature dependence of T1 is classified into three regimes: (a) for ( )-relaxation mechanism follows modified Korringa relation due to EEI and disorder. 1 H-T1 is due to the electron-nuclear dipolar interaction in addition to the contact term. (b) for intermediate temperature rangeμ 〈 T 〈 TBPP, the temperature where the contribution from the reorientation motion to the T1 is insignificant) -relaxation mechanism is via spin diffusion to the paramagnetic centers (SDPC) and (c) in the high temperature regime and atlow Larmor frequency-the relaxation follows the modified Bloembergen, Purcell and Pound (BPP) model.T1 data analysis has been carried out in the light of these models depending upon the temperature and frequency range of study.Fluorine relaxation data has been analyzed and attributed to the PF6 reorientation. The cross relaxation among the 1 H and 19 F nuclei has been observed in the entire temperature range suggesting the role of magnetic dipolar interaction modulated by the reorientation of the symmetric molecular sub-groups.The data analysis shows that the enhancement in Korringa ratio is more in less conducting sample. Intra and inter chain hopping of charge carriers is found to be a dominant relaxation mechanism at low temperature. Frequency dependence of