The Isomer Chemistry of Magic-Sized Clusters

Magic Sized Clusters (MSCs) are small sized inorganic nanoparticles which are less 2 nm in size with a thermodynamically stable structure. Their highly surface-dependent properties facilitate the existence of various types of isomers. Particularly, isomers which exhibit dissymmetric circular dichroism signals, also known as optical isomers, are of great importance. Chiral MSCs with large circular dichroism signals will be discussed as compared to other chiral semiconductor nanocrystals. To investigate the chiroptical origins of our chiral MSCs, characterizations including XRD and Raman were conducted to explore ligand geometry and structural properties. By surface characterizations including FT-IR and TGA, we have found that particular mode of surface ligand binding is critical for the chirality. Low crystal symmetry of MSCs is thought to induce the large transition dipole moment of MSC, which in turn yields high chiroptical activity. In contrast, similar sized QDs showed silent chirality presumably due to the high crystal symmetry and the consequent low transition dipole moment. Propagation of chirality using chiral MSCs as the building block will be also addressed. We believe that unique characteristics of MSCs may open a new avenue in designing and synthesizing unprecedented chiroptical materials.