Giant Grain Growth of 2,5-Di(2-thienyl)-1H-pyrrole Crystal Films: Kinetic Analysis of Self-Crystallization from Its Supercooled Liquid in Vacuum Deposition

Self-crystallization of 2,5-di(2-thienyl)-1H-pyrrole (DTP) from its supercooled liquid in vacuum deposition was demonstrated. In situ infrared absorption spectroscopy and polarizing microscope observation techniques were employed to investigate the kinetic effect of three kinds of substrates whose surfaces were differently treated on the phase transformation during deposition. Essentially, irrespective of the kind of substrates, the crystallization was found to proceed in a steady-state manner, where the supercooled liquid could be regarded as an intermediate whose amount was kept almost constant during the deposition. After stopping the deposition, the supercooled liquid underwent further phase transformation to complete the crystallization, which process could be well understood with the Avrami model. Giant grain growth of DTP crystal films was found on a substrate, which was uniformly covered with a thin ionic liquid layer, and their crystallinity was much improved.