We examine the nonlinear optical properties of solutions of 9,10‐anthraquinone, 1,4‐dihydroxy‐anthraquinone, 5,8‐dichloro‐1,4‐dihydroxy‐anthraquinone and 1,4‐bisethylamino‐anthraquinone by means of the intensity‐dependent transmission and the Z‐scan method with 532 nm 8 ns pulses. The results demonstrated that the 9,10‐anthraquinone displayed a two‐photon absorption (TPA) character. The molecular TPA cross section of this compound is estimated as σ2 = 7.22 × 10−19 cm4/GW or σ2 = 26.96 × 10−48 cm4/photon/s, respectively, and an essential state of ‘m1Ag’, which should be located near the 2ω virtual transition state, is predicted. On the other hand, the effective excited‐state nonlinear refractive coefficients n2eff of these anthraquinones are found to be ∼10−10 esu, which are comparable with those highly conjugated planar molecules of tetrabenzporphyrins and phthalocyanines.

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