In this work, we studied by means of density functional theory (DFT) and time-dependent DFT(TD-DFT) using the effect of the mixture composition C4mimBF4/acetonitrile on the charge transfer in Coumarin 153(C153) after photoexcitation. The mixture composition was characterize by their corresponding static dielectric constant Em . The PBE0 and M06-2X functionals combined with linear response (LR) and state specific (SS) solvation schemes were used to obtain various electronic properties of C153 in both ground and excited states. Our results show that the calculated fluorescence Stoke shift, using the state specific solvation scheme correlates well with the corresponding experimental data obtained for C153 dissolved in other solvents have the same static dielectric constant as of the C4mimBF4/acetonitrile mixture. The charge transfer was quantified using descriptors such as charge qCT, distance dCT, and the dipole moment μCT between the ground and the excited state. These descriptors were calculated based on four different partial atomic charge models, namely Mulliken, Natural Populations Analysis, Hirshfeld, and Merz–Kollman. The charge transfer also was quantified using descriptors based on the electrostatic surface potential namely the polarity index. Both PBE0 and M06-2X functionals combined with the Linear Response solvation scheme result in a systematic increase of the qCT, dCT, and μCT with increasing Em, while they decrease for most of the partial atomic charge models when the State Specific solvation scheme is used. This later result points out that this solvation scheme is not suitable for the description of the excited state of C153 in this mixture. Our results show that the extent of change of these descriptors is small and indicates that the effect of the mixture composition on the charge transfer in C153 is weak.