We modified structure of nonlinear optical chromophore by attaching alkyl groups to improve the shelf lifetime while keeping a low glass transition temperature. We obtained a sample with modified NLO, 4-(2-ethylhexyloxy)-3-propyl-1-(4'-nitoro phenylazo)benzene (m3p2,6) which has a longer shelf lifetime of more than five months. In PVK:m3p2,6:BisCzPro:TNF (50:46:3:1 wt%) composite, the photorefractive response rate was 33 ms and diffraction efficiency was 49%, at an electric field of 100 V/µm and a total writing intensity of 942 mW/cm<sup>2</sup>. These results of high-performance should be due to the following reasons: first, the chromophore m3p2,6 acts as a plasticizer and has a larger free volume thereby enhancing the orientation of chromophore, and second, the solubility of the chromophore in polymer matrix increases, inhibiting crystallization.
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