Molecular motions with large amplitude in close-packed crystals accompany large distortions of the molecular configuration, which generally generate orientational structural transitions between diverse states and enable the tuning of their bulk physical properties. We present a flexible organic dielectric, di-n-butylammonium chlorodifluoroacetate (1), which exhibits a reversible temperature-induced spontaneous polarization switching at 243 K (Tc). Ferroelectric hysteresis loop measurements and second harmonic generation experiments reveal its excellent polarization switching capacity with spontaneous polarization of 3.9 μC cm–2. Temperature-dependent solid-state nuclear magnetic resonance measurements clearly elucidate the dynamical mechanism of polarization switching of 1. Above Tc, an active swinglike motion in long-chain di-n-butylammonium (DBA) cation is confirmed, resulting in complete obliteration of the dipole moments. When the temperature decreases below Tc, the swinglike motions are frozen and th...