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 sel f-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 chro mophore (polydiacetylene backbone) orientation and third-order optical nonl inearity of poly-DCHD/PDAC multilayers are investigated by electroabsorptio n spectroscopy. The ratio of X-3333((3)), to X-1133((3)) is significantly l ess than 3, indicating that the polymer chains are predominantly parallel t o the plane of the substrate. In addition, the films possess third-order no nlinearity in the order of 10(-11) esu.