Dynamical disorder of pi-molecular structures induced by proton dynamics in an organic ferroelectric compound

We have investigated the optical response resulting from the proton-$\ensuremath{\pi}$-electron-molecular-skeleton coupled dynamics in an organic ferroelectric 55DMBP-Hia. Upon the ferroelectric-to-paraelectric transition, almost all of the vibrational modes below $500\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$ are anomalously blurred and amalgamated into the high-frequency tail of the polarization-relaxation mode. This indicates that the constituent molecular shape is no more well defined around ${T}_{C}$ due to the dynamical disorder of the $\ensuremath{\pi}$-conjugated structure originating from proton delocalization on the intermolecular bifurcated hydrogen bond.