Enhanced fluorescent emission of organic nanoparticles of an intramolecular proton transfer compound and spontaneous formation of one-dimensional nanostructures

Nanoparticles of intramolecular proton transfer molecule N,N'-bis(salicylidene)-p-phenylenediamine have been prepared with the reprecipitation method in water. The evolving processes have been monitored by means of UV-vis absorption, fluorescence emission, transient emission spectroscopy, and scanning electron microscopy. The fluorescent intensity is increased beyond 60 times in the nanoparticles compared to that in solution. With the increase of aging time, nanoparticles convert spontaneously from spherical to rodlike and finally to beltlike aggregates. A mechanism for the enhanced emission is proposed on the basis of flattened molecules, and a possible model for change of the nanoparticles' shape is also proposed on the basis of theoretical calculations.