Two-Photon Absorption and Excited-State Refractions in Anthraquinone Dyes

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.