Large third-order nonlinear optical response of conjugated copolymers consisting of fluorene and carbazole units

Off-resonant third-order nonlinear optical properties using degenerate four-wave mixing measurements in solution at 1064 nm have been studied for novel π-conjugated, processible, optically transparent and thermally stable copolymers constituted of carbazole and fluorene. The second-order hyperpolarizability γ1111 per repeat unit of the polymer containing alkyne segment (Cz-PFE) is as high as 6.5×10−31 esu. The large nonlinearity of Cz-PFE is attributed to its rigid planar and intrachain charge transfer structure.