Martensitic-like transition between liquid crystalline and crystalline phases of organic semiconductor HAT6 

Martensitic transformations are diffusionless phase transitions typically observed in solid-state systems such as metallic alloys. While such transformations are well-understood in the solid-state, their occurrence in liquid-solid transitions remains largely unexplored. In this study, we investigate a Martensitic-like transformation during the phase transition of a discotic liquid crystal, hexakis(n-hexyloxy) triphenylene (HAT6), from a columnar hexagonal (Col_H) phase to a crystalline state. When confined within lithographically fabricated microchannels, HAT6, in the Col_H phase, exhibits in-plane molecular alignment. Moreover, the alignment order is transferred to the crystalline phase under rapid cooling. Notably, crystal growth occurs via discrete, step-like bursts, indicative of avalanche-like kinetics, resembling the sudden and large-scale rearrangements observed in phenomena such as earthquakes. Under rapid quenching, the crystal growth rate exceeds predictions of the Burke–Broughton–Gilmer (BBG) model by up to 10⁷ times. This Col_H - Crystal transition shows four hallmarks of Martensitic transformations: orientational correlations, reversibility, strong cooling rate dependence, and avalanche-like kinetics. We propose the transition proceeds via a Martensitic-like mechanism—marking, to our knowledge, the first solidification transition to do so. This may enable rapid growth of large single crystals for organic electronics and memory.