Organic nanoparticles have attracted tremendous research interests over the past few years owing to their special properties which lie between the properties of molecules and those of bulk material. The electronic properties of organic nanoparticles differ fundamentally from those of inorganic ones. Organic nanocrystals allow much increased variability and flexibility in synthesis of materials, preparation of nanoparticles, and investigation of their physico-chemical properties. The ordered periodic mesoscopic materials allow the construction of composites with many guest types like organic molecules or polymers. These guest/host materials combine high stability of the inorganic host system, new structure forming mechanism due to the confinement of guests in well-defined pore channels. This book consists of two parts. The first part of this study constitute synthesis and photophysical characterization of fluorescent organic nanoparticles of conjugated compounds and rod-coil molecules. The second part deals with the self-assembled organic-inorganic functional hybrid nanocomposites. This book is useful for the materials scientists and for inter-disciplinary research.