Fabrication of organic microcrystals and their optical properties

Organic microcrystals occupy the mesoscopic phase between a single molecule and bulk crystal, and they are expected to exhibit peculiar optical- and electronic-properties, depending on crystal size. The reprecipitation method was available for fabrication of organic microcrystals. The crystal size was in the range of about ten nanometer to several hundred nanometer. The excitonic absorption peak positions were shifted to short-wavelength region with decreasing crystal size. This phenomenon is not explainable by quantum confinement effect, and it is now speculated to be due to a certain coupled interaction between exciton and lattice vibration in thermally softened microcrystal lattice.