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Abstract In this paper, alkyl groups with different lengths are introduced to the two-dimensional spindle-type chromophores as the steric isolators to improve the poling efficiency and long term stability of the poled polymers for second-order nonlinear optical materials. The structure and thermal properties of alkyl functionalized chromophores are characterized by the 1H NMR, FT-IR, UV–Vis, DSC, TGA et al. The chromophores with different alkyl groups present extremely similar maximum absorbance wavelength (480 nm), which means they have very similar first-order hyperpolarizability. Guest-host polymer doped with chromophores has been prepared. Those materials display different glass transition temperatures and good thermal stability. According to the electro-optic coefficients studies and poling efficiency results, chromophores with longer alkyl side chain groups exhibit better poling efficiency and larger electro-optic coefficients. Especially for the chromophores with octyl group, the poling efficiency increases up to 3 times compared to the reference chromophore 2-(3-{2,5-Phenylmethanol-4-[4-(dimethylamino)styryl]-styryl-5,5-dimethylcyclohex-2-enylidene)malononitrile (STC), while the corresponding electro-optic coefficient of the poled polymers increases up to 4 times, indicating a significant effect of the isolate groups on improving the poling efficiency. Highlights • We synthesized a series of two-dimensional spindle-like chromophores with different length of alkyl groups. • Two-dimensional spindle-like chromophores had good thermal stabilities and met the requirements of the poling process. • Chromophores with longer alkyl groups and linear alkyl group had better long-term stability, poling efficiency and larger electro-optic coefficient. • Poling efficiency of chromophores with octyl group increased up to 3 times and electro-optic coefficient of poled polymers increased up to 4 times compared to STC. [ABSTRACT FROM AUTHOR]