Low-energy excitations in electron-doped metal phthalocyanine from NMR in Li${}_{0.5}$MnPc

${}^7$Li and ${}^1$H NMR and magnetization measurements in \lpc (Pc$\equiv$C${}_{32}$H${}_{16}$N${}_8$), recently proposed as a strongly correlated metal, are presented. Two different low-frequency dynamics are evidenced. The first one, probed by ${}^1$H nuclei gives rise to a slowly relaxing magnetization at low temperature and is associated with the freezing of MnPc $S=3\mathrm{/}2$ spins. This dynamic is similar to the one observed in pristine $\beta$-MnPc and originates from Li depleted chain segments. The second one, evidenced by ${}^7$Li spin-lattice relaxation rate, is associated with the hopping of the electrons along Li-rich chains. The characteristic correlation times for the two dynamics are derived and the role of disorder is briefly discussed.