We report theoretical investigations on the effect of H --> F substitution in acetylacetonate ligands in order to understand why fluorination promotes the extraction of uranyl to supercritical CO2 with a marked synergistic effect of tri-n-butyl phosphate "TBP". The neutral LH and deprotonated L- forms of the ligand, and the uranyl complexes UO2L2 and UO2L2S (S = H2O versus trimethyl phosphate "TMP" which mimics TBP) are studied by quantum mechanics (QM) in the gas phase, whereas the ligands LH and their UO2L2 and UO2L2S complexes are studied by molecular dynamics (MD) in SC-CO2 solution as well as at a CO2-water interface. Several effects are found to favor F ligands over the H ligands. (i) First, intrinsically (in the gas phase), the complexation reaction 2 LH + UO22+ --> UO2L2 is more exothermic for the F ligands, mainly due to their higher acidity, compared to the H ligands. (ii) The unsaturated UO2L2 complexes with F ligands bind more strongly TMP than H2O, thus preferentially leading to the UO2L2(TMP) complex, more hydrophobic than UO2L2(H2O). (iii) Molecular dynamics simulations of SC-CO2 solutions show that the F ligands and their UO2L2 and UO2L2S complexes are better solvated than their H analogues, and that the UO2L2(TBP) complex with F ligands is the most CO2-philic. (iv) Concentrated solutions of UO2L2(TBP) complexes at the CO2-water interface display ail equilibrium between adsorbed and extracted species, and the proportion of extracted species is larger with F- than with H- ligands, in agreement with experimental observations. Thus, TBP plays a dual synergistic role: its co-complexation by UO2L2 yields a hydrophobic and CO2-philic complex suitable for extraction, whereas TBP in excess at the interface facilitates the migration of the complex to the supercritical phase.