Electrostatic Self-Assembly of Polydiacetylene Nanocrystals: Nonlinear Optical Properties and Chain Orientation

Abstract

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 to 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.