Optical properties of a 2,6-dihydroxyanthraquinone single crystal

A study has been made on the polarization dependence and the temperature dependence of absorption and luminescence spectra of a 2,6-dihydroxyanthraquinone single crystal. The single crystal structure has been investigated by X-ray diffraction and is assigned as monoclinic and the space group P2₁/c (#14). Electronic energy levels were calculated by molecular orbital calculation program of WinMOPAC. The absorption band at 3.2eV and the luminescence band at 2.2eV are assigned mainly to the transition between HOMO and LUMO states. The anisotropic effect on the absorption and luminescence was analyzed in view of the crystal structure. The polarization dependence is consistently explained by the direction of transition dipole moment of 2,6-dihydroxyanthraquinone molecule.