Nonlinear optical properties of complexes of π‐conjugated polymers

Abstract

AbstractNovel host–guest complexes of conjugated polyimines with gallium chloride have been proposed and studied as an approach to enhance the third‐order nonlinear optical properties of the host conjugated polymers. The third‐order nonlinear optical susceptibility χ(3) (–3ω;ω,ω,ω) of two conjugated polyimines and their GaCl3 complexes, measured by third harmonic generation spectroscopy in the wavelength range 0.9 ∼ 2.4 μm, shows that χ(3) is enhanced in the nonresonant region, whereas it is reduced in the resonant region due to complexation. These results are explained by complexation mediated modifiction of the electronic structure of the host polymers. Two theoretical models consisting of four electronic energy levels were found to give a good description of the frequency dispersion and resonances in the χ(3) (–3ω;ω,ω,ω) spectrum of the host–guest complexes. The resulting fitting parameters were used to predict the degenerate four wave mixing χ(3) (–ω;ω,–ω,ω) spectrum for the new materials. The results of the present study suggest that host–guest complexation is a promising approach for improving the third‐order nonli‐near optical properties of conjugated polymers.