Electrostatic self-assembly of polydiacetylene nanocrystals: Nonlinear optical properties and chain orientation

Two different sizes of nanocrystals of poly(1,6-dicarbazolyl-2,4-hexadiyne) (poly-DCHD), have been assembled into composite films by electrostatic self-assembly (ESA) using poly(dimethyldiallylammonium chloride) (PDAC) as the oppositely charged polyelectrolyte. UV-visible absorption showed that: the film deposition process is uniform. The AFM images of these films indicate that the nanocrystals are platelets lying on the substrate plane. The chromophore (polydiacetylene backbone) orientation and third-order optical nonlinearity of poly-DCHD/PDAC multilayers are investigated by electroabsorption spectroscopy. The ratio of X-3333((3)), to X-1133((3)) is significantly less than 3, indicating that the polymer chains are predominantly parallel to the plane of the substrate. In addition, the films possess third-order nonlinearity in the order of 10(-11) esu.