Abstract

A continuing problem has been to develop new conjugated polymers with enhanced nonlinearity and stability. In highly ordered films where the conjugated chains are aligned the nonlinear response can be greatly enhanced in the direction of alignment. The Langmuir-Blodgett. technique has been shown to be effective for the preparation of thin ordered films. Polythiophenes belong to a relatively new class of π-electron conjugated polymers that show large and fast electronic χ⁽³⁾ comparable with those of polydiacetylenes. The introduction of oxygen atoms in different functional groups on the side chain of poly(3-alkylthiophene) (PAT) improves PAT adhesion with water, making possible the fabrication of LB structures. Bolognesi et al.¹ have shown that the presence of an ether function in the PAT side chains results in LB multilayers showing a good orientation of the main chain in the dipping direction.² Following this technique a new modified PAT structure (poly[3-(6 - tetrahydropyraniloxyhcxyl)] - 2,5 - thienyleue) (see Fig. 1) has been prepared and we report here on the characterization of the nonlinear optical response of this material. The films consisted of eight monolayers for a total thickness of about 130 Å. Dichroic ratios up to three were observed with an order parameter of about 0.40. The polyenic backbone was mainly oriented parallel to the substrate (and the dipping direct ion) and was highly planar.

© 1997 Optical Society of America