Organic crystals: Synthesis and geometry-dependent property changes

Scaling down the size of a bulk material into quantum size regime grants new optical and electrical properties due to the emergence of discrete electronic energy states according to the quantum size effect. Another way to secure new optical, electrical and chemical properties is to design and grow highly crystalline low dimensional structures from individual ensemble molecules, which is known as meso size effect. The meso size effect is especially of great interest for highly conjugated pure or metal containing organic molecules. For example, we have recently demonstrated that C70 molecules are directly crystallized into well-defined cube crystals in solution phase, and the C70 cubes emit unprecedented strong photoluminescence (PL) due to the reduced exciton scattering sites by the crystallization. In this presentation, I will introduce our recent results that further demonstrate the exhibition of new optical and chemical properties upon the crystallization of pentacene and zinc phthalocyanine (ZnPc) molecules into 1D wires, which show crystal plane-specific PL/electrical photoresponse and surprisingly increased water dispersibility, respectively. The synthetic process as well as light-molecule interactions involved in the crystal plane-dependent PL activity from pentacene 1D wire and the application of water dispersible ZnPc nanowires as an efficient photosensitizer for cancer phototherapy will be discussed in detail.