The ground state thermodynamic stabilities of intermolecular charge transfer complexes between acceptor molecule pyrene and donor molecules phenothiazine and promazine have been investigated with DFT methods. Their vertical singlet-singlet transitions have been calculated and characterized employing TD-DFT methods, as well. In the ground state, pyrene forms slightly stable intermolecular complexes with phenothiazine and promazine in the gas phase. The phenothiazine-pyrene, [phtz-pyr], and promazine-pyrene, [pmz-pyr], complexes are 3.76 and 2.75 kcal/mol more stable compared to their reactants, respectively. For both of the complexes, the most probable four transitions belong to the local excitations (LE) within donor or acceptor molecules. However, the S(0) -> S(1) transitions with excitation wavelengths of approximate to 448 nm for [phtz-pyr] and approximate to 425 nm for [pmz-pyr] are pure CT transitions between the frontier molecular orbitals of donor and acceptor molecules. The S(0) -> S(1) transitions with an excitation wavelength of approximate to 337 nm for [phtz-pyr] and approximate to 345 nm for [pmz-pyr] are also CT transitions and the charge transfer occurring in the [pmz-pyr] complex is an n -> pi type while the character of CT transition in the [phtz-pyr] complex is purely pi -> pi. (C) 2010 Elsevier B.V. All rights reserved.