Nanoscale crystallization and thermal behaviour of 1,2,4,5-tetrabromobenzene

Nanocrystals of the thermosalient (TS) material 1,2,4,5-tetrabromobenzene (TBB) with diameters of 20, 100 and 200 nm were prepared by using nanoporous anodic aluminum oxide (AAO) templates. In contrast with bulk crystallization, which mainly affords single crystals of TBB in the stable phase β, two-dimensional X-ray microdiffraction revealed exclusive formation of polycrystalline TBB in the less stable phase γ inside the AAO nanopores. While bulk crystals of TBB undergo TS transition from phase β to γ at 41 °C and melt at 180 °C, the nanocrystals of phase γ TBB remain stable from cryogenic temperatures to nearly 80 °C and sublime at higher temperature. This study reveals fundamentally different crystallization and thermal behaviour of the TS materials at the nanoscale compared to the macroscale.