42 - Fabrication technique of organic nanocrystals and their optical properties and materialization

Abstract

This chapter focuses on the reprecipitation method and describes the related technique to fabricate organic and polymer n-conjugated nanocrystals. The reprecipitation method is a pure chemical technique used to prepare organic nanocrystals by injecting a solution of the target compound into a poor solvent. The characteristics of the reprecipitation method are that it is simple, quick, and inexpensive, and can be used for nanocrystallization of various kinds of organic compounds. In this method, the size and morphology of nanocrystals can be controlled by changing experimental conditions such as combinations between poor and good solvents, concentration of injected solution, and temperature of poor solvent. A reprecipitation method for preparing DCHD nanocrystals is presented, in which 200 gL of acetone solution (0.1–10 M) is injected into 10 mL of well-stirred distilled water at room temperature, which produces amorphous DCHD nanoparticles in water by SEM observation. This shows that poly-DCHD nanocrystals with controlled size can be produced by controling both the concentration of solution and temperature of a poor solvent. The SCF crystallization (SCFC) method is also explained, where the nanocrystals are fabricated by the reprecipitation into a poor solvent with cooling down after the target compounds are dissolved in SCF. Well-defined organic nanocrystals fabricated by the reprecipitation method are expected to be applied as practical industrial products in the various fields of pigments, ink, organic photoconductor materials, medical supplies, and agricultural chemicals.