The ground state geometries, frontier molecular orbital properties, and absorption properties of 4,4′-（ethane-1,2-diylbis（oxy））dibenzaldehyde （EDO-DBDHD） and its polymorph have been studied theoretically. The density functional theory （DFT） method was employed to optimize the ground state geometries, and theoretical data reveal that EDO-DBDHD features the planar molecular conformations, in contrast to V-shaped structures of its polymorph, which agrees with the experimental data. Additionally, the absorption spectra of both compounds were predicted using time-dependent density functional theory （TDDFT）. The calculated results show that the lowest lying absorption bands of these compounds have the transition configurations of HOMO → LUMO, resulting in the transition character of π→π＊/n→π＊. The transition of HOMO → LUMO＋3 mainly contributes to the highest lying absorption bands of two compounds at 225 nm with the character of π→π＊/n→π＊.
