Off-resonant third-order nonlinear optical properties using degenerate four-wave mixing measurements in solution at 1064 nm have been studied for novel pi-conjugated, processible, optically transparent and thermally stable copolymers constituted of carbazole and fluorene. The second-order hyperpolarizability gamma(1111) per repeat unit of the polymer containing alkyne segment (Cz-PFE) is as high as 6.5 x 10(-31) esu. The large nonlinearity of Cz-PFE is attributed to its rigid planar and intrachain charge transfer structure. (C) 2002 Elsevier Science B.V. All rights reserved.