The ground states of TiO₂ molecule under different electric fields are optimized using density functional theory DFT/B3P86 at 6-311＋G* level. Based on the optimized molecular geometries, the transition wavelengths and oscillator strengths of the first six different excited states for TiO₂ molecule are studied by employing the revised hybrid single-excitation configuration interactions, i.e. CIS-B3P86 method with basis set 6-311＋G*. It is shown that the many excited states of TiO₂ molecule satisfied the selection rules of electric dipole radiation, manifold transition spectra would come forth when transitions from excited states to ground state of TiO₂ molecule took place. Therefore, the new functional materials at molecular dimension level will enhance the sunlight absorption ability. When the external electric field strengths become stronger, the energy gaps between the highest occupied molecular orbital HOMO and the lowest unoccupied molecular orbital LUMO will become smaller and the electrons of the occupied orbital are more apt to be excited to the virtual orbital. The transition wavelengths of the first six excited states for TiO₂ molecule shift from ultraviolet region to visible one, the longest wavelength achieves 589 nm. Therefore the luminescence spectrum of TiO₂ molecule can be expanded in visible light region by the use of external electric fields.

Key words: TiO₂, electroluminescence, excitation properties, transition wavelength