Preparation of polydiacetylene microcrystals and their properties

Microcrystals of solid-state polymerizable diacetylene compounds have been successfully prepared by a reprecipitation from their acetone solution in water, and were converted into polydiacetylene microcrystals dispersed in water. Effect of size-determining factors such as concentration of solution and temperature of water were investigated. Based on the results, microcrystal formation mechanism, i.e. first reprecipitation of amorphous microparticles, followed by the competing processes of crystallization in particle and adhesion of particles, was suggested. Some characteristic features of the microcrystals, compared with those of large bulk crystals, have been revealed: for example, excitonic absorption of polydiacetylenes took place a blue shift with decreasing size, in almost one order of magnitude larger size range than those of metals and semiconductors. It has also been demonstrated that polydiacetylene microcrystal dispersion gives good enough optical quality to conduct optical Kerr-shutter experiment, and the large X⁽³⁾ value of ca. 10^-9 esuM^-1 at a nonresonant wavelength was clarified.