Diisopropylammonium bromide (DIPAB) molecular ferroelectric single crystals were prepared. Temperature-dependent domain evolutions were observed in situ by polarized light microscopy. Fast color variations were found both in heating and cooling processes. The color-variation temperatures agreed well with the phase transition temperatures that took placed in the dielectric measurement, which demonstrated that the fast domain transitions were exactly the ferroelectric-parroelectric phase transitions. Quick changed birefringence of the crystal was the main cause for the color variation of the domains during the phase transitions. In addition, 180 degrees domains were detected by piezoresponse force microscopy, which were proposed to minimize the depolarization field. (C) 2017 Elsevier B.V. All rights reserved.