Abstract: The search for ways to control the size, shape and hence properties of organic molecular crystals, well established for inorganic crystals, is an important aspect of possible developments in nanoscience. Using functional low molecular weight organic molecules we have successfully prepared a series of monodisperse nanoparticles with controllable size and shape. Their electronic states have been studied and mapped as a function of nanoparticle size. We find their organic nanoparticles also possess significant size effects, including optical size effects which may have useful applications in optoelectronic devices, and in the study of fundamental processes in conventional organic molecular crystals.