Ionic liquid-assisted vapor deposition and polymorphs control of 2,2′:5′,2″-terthiophene crystals

In this work we investigated possible effects of nanoscale ionic liquid (IL) on the crystal growth of 2,2′:5′,2″-terthiophen (3T), a well-known oligomer source for conducting polymers, and its polymorphs control (high- and low-temperature phases, respectively) in vapor deposition. In the vapor deposition via a bulky IL droplet as well as without IL, the low-temperature phase was dominant at a deposition temperature as low as 6 °C-7 °C, and there were large 3T platelet single crystals (several tens of μm in size) of the low-temperature phase obtained in the bulky IL droplet. In contrast, when 3T molecules were deposited via thin film IL in the thickness range of 1-100 nm, the high-temperature phase could be much stabilized even at a deposition temperature of 6 °C, and especially for a few nm thick IL a nearly single high-temperature phase of 3T crystal films was effectively obtained.