Effect of orientational order of tris(8-hydroxyquinolinato)aluminum(III) on electroabsorption

Abstract

The electroabsorption (EA) spectrum was analyzed in terms of the orientational order of tris(8-hydroxyquinolinato)aluminum(III) (Alq 3) molecules, where the orientational order parameter 〈 P n ( cos θ ) 〉 ( θ: the tilt angle of molecule; P n : nth Legendre polynomial; 〈 〉 : thermodynamic average) was used to quantify the anisotropic orientational order of Alq 3. It was shown that the EA intensity is a function of S 1 and S 2 at the modulation frequency ω, whilst it is a function of S 2 at the second-harmonic frequency 2 ω. The EA spectrum for the vacuum deposited Alq 3 was obtained from the optical transmittance measurement. The results suggested that the spontaneous polarization of Alq 3 is generated in the evaporated films.