The transient absorption spectra and photoinduced electron-transfer process of duroquinone (DQ) in mixed binary solutions of ionic liquid (IL) [bmim][PF6] and acetonitrile (MeCN) have been investigated by laser photolysis at an excitation wavelength of 355 nm. A spectral blue shift of (3)DQ* was observed in the IL/MeCN mixtures compared to MeCN. At lower V-IL(volume fraction of IL), the interaction between DQ and the solvent is dominant, and the decay rate constant (k(obs)) of (3)DQ* increases steadily with the increasing of V-IL; to the contrary, at higher V-IL, the network structures due to the hydrogen bond and viscosity are dominant, and the decay rate constant decreases obviously with increasing V-IL. A critical point (turnover) was observed at V-IL = similar to 0.30. The dependence of the observed growth rate (k(gr)) of the photoinduced electron-transfer (PET) products on V-IL is complex and shows a special change; k(gr) first decreases with increasing V-IL, then increases, and finally decreases slowly with further increasing of V-IL. It is speculated that the PET process in the mixture can be affected by factors including the local structure and the reorganization energy of the solvent and salt and cage effects. The change of local structure of [bmim][PF6]/MeCN is supported by following the steady-state fluorescence behavior of the mixture, in combination with the molecular dynamics simulation of the thermodynamic property. The results revealed that the degree of self-aggregation of monomeric cations (bmim(+)) to associated forms increases with increasing V-IL. This is in good agreement with the laser photolysis results for the same solutions.