The strong tendency of organic nanciparticles to rapidly self-assemble into highly aligned superlattices at room temperature,In when solution-cast from dispersions or spray-coated directly onto various substrates is described. The nanoparticle dispersions are stable for years. The novel precipitation process used is believed to result in molecular distances and alignments in the nanoparticles that are not normally possible. Functional organic light-emitting diodes (OLEDs)-which have the same host-dopant emissive-material composition-with process-tunable electroluminescence have been built with these nanciparticles, indicating the presence of novel nanostructures. For example. only changing the conditions of the precipitation process changes the OLED emission from green light to yellow.