In contrast, the II-III phase transition (Figure , Movies S3,4) showed nucleation at several points within the crystal and transformed over several minutes, with polymorph III increasing in brightness under polarized microscopy. The II-III transition exhibited no clear phase boundary, instead we observed a diffuse spreading of the intensely bright polymorph III. The most common nucleation points are near the edges of the crystal, though cracks and other defects will act as nucleation spots (Figure ) as well. By tracking the intensity change over temperature, we observe a quite smooth change, with no avalanche like behavior (Figure ). Upon cooling, the reverse transition began at a temperature below that of the I-II transition, exhibiting a hysteresis of 100 °C, an order of magnitude greater than the I-II transition which showed a hysteresis of only 17 ± 5 °C, confirming a much larger energy barrier for nucleation and growth mechanism. This matches with observations from DSC using powder samples, showing a hysteresis for the I-II and II-III transitions of 6°C and 75 °C, respectively . In single crystals, the hysteresis for the II-III transition varied substantially and, in some cases, the III-I transition did not occur during constant cooling, resulting in the kinetic trapping of polymorph III at room temperature. This suggested a nucleation and growth behavior, shown in Figure , where nucleation occurred at edges or defects and diffusively spread through the crystal. Thermosalient behavior. Upon undergoing the I-II transition, we found the crystal decreased in length by 3.6 ± 1.3% on average (Figure , Table ). This change in length was matched quite closely with the 2.9% decrease in the b-direction of the unit cells obtained through fitting the thin film GIXD diffraction patterns (Figure ), as we previously reported . This shape change led to cracking of pinned small crystals of ~100 µm in size (Figure , Movie S5), which occurs due to the buildup of strain at the phase front caused by the change in shape coupled with crystal-substrate interactions that act to prevent the shape change. In an extreme case, we observed a crystal embedded in a surrounding film that formed during the drying process, which cracked upon transition. This case also resulted in the formation of "bright bands" along the phase boundary, visible in Figure , which would be consistent with strain induced birefringence we expect from a crystal attempting the I-II transition while trapped in a solid film. On the other hand, for unpinned large crystals (1-3mm), we observed a pronounced thermosalient behavior during the I-II transition (Figure , Movie S6). While the crystal will bend during the I-II transition, reversing the transition will not recover original shape, implying a plastic deformation. This may be a result of strain buildup at the phase boundary causing the π-stacks within the crystal to irreversibly slip along the greasy alkyl chain layers.