Organic crystalline solids have great potential for application to photonic and electronic devices. There have been many reports on preparation processes of organic crystalline solids, such as vapor and liquid processes. Minemawari et al. have recently reported organic crystals prepared using an ink-jet process.(1) Using this process, they demonstrated that mixing fine droplets of a poor solvent and a solution of an active semiconducting component can trigger the controlled formation of exceptionally uniform single crystal or polycrystalline thin films that grow at liquid-air interfaces.

Thiophene/phenylene co-oligomers (TPCOs) are expectable materials that have practical application to photonic and electronic devices. We have been studying the process of crystallizing TPCOs and have been developing more efficient processes of crystallizing them. Here, we report crystallization of TPCOs by mixing droplets of the poor solvent and the TPCO solution. The TPCO compound used in the present study was 2,5-bis(4-biphenylyl)thiophene (BP1T). BP1T was crystallized as follows: we first dropped N,N-dimethylformamide as a poor solvent onto a 1 × 1 cm² glass substrate to cover its surface. Three droplets of a chlorobenzene solution of BP1T were then consecutively dropped onto the poor solvent, mixing the poor solvent and BP1T solution. The chlorobenzene and poor solvent were then evaporated yielding the BP1T crystal on the glass substrate. The solubility of BP1T in chlorobenzene at 110°C was 4.1 mM. Dropping the 110°C chlorobenzene solution onto the poor solvent on an 80°C substrate formed a large planar BP1T crystal. Figure 1 shows the polarizing micrograph of the BP1T crystal on the glass substrate, and the crystal was 550 μm in size. The drying time of the sample was about 10 min. This method is efficient for preparing TPCO crystals on substrates.

Reference

(1) H. Minemawari et al., Nature, 475 (2011) 364.

Keywords: Thiophene/phenylene co-oligomer, Crystallization, Solution, Poor solvent

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