The electrostatic attraction between the separated charges in long-range excited charge-transfer states originates from the non-local Hartree-Fock exchange potential and is, thus, a non-local property. Present-day time-dependent density functional theory employing local exchange-correlation functionals does not capture this effect and therefore fails to describe charge-transfer excited states correctly. A hybrid method that is qualitatively correct is described.

The absorption spectra of neutral pentacene (C 22 H 14 ) and its radical cation (C 22 H 14 + ) and anion (C 22 H 14 -) isolated in solid Ne, Ar, and Kr have been measured from the ultraviolet to the near-infrared. The associated vibronic band systems and their spectroscopic assignments are discussed together with the physical and chemical conditions governing molecular anion production in matrices doped with alkali metal (Na or K). TD-DFT calculations were carried out to assist in the assignments for the measured spectral features of the pentacene ions.