The chemical reaction of thioindole and [20] fullerene and the use of DFT to estimate some quantum chemical descriptors

In this study, the solvent effects are probed on the chemical reaction of the (E)-3-thiophene-2-yl-indoline-2-thione (I) and [20] fullerene, and the resulted complex (I_a) via the density functional theory (DFT). To characterize the synchronicity of the reaction and its correlation with activation energy, we estimated the energy barrier of transition states (E_TS1^≠ and E_TS2^≠) in the used solvents. The highest E_TS1^≠ and E_TS2^≠ value are found in water solvent, whereas the lowest E_TS1^≠ and E_TS2^≠ value are considered in the gas phase. Formation of the TS2 appears energetically less favorable due to the non-bonding electrostatic repulsion among the sulfur heteroatoms and C₂₀, also the π–stacking between the thiophene ring and nanocage, which affects the stability of the TSs. The most thermodynamic stability, the adsorption energy difference among liquid phase and gas phase (ΔE_l-g = E_l − E_g), and the most polarity (µ) belongs to stabilizing effect of water solvent on I_a, whereas the lowest thermodynamic stability, the lowest released ΔE_l-g and the least polarity belongs to optimization of I_a in the gas phase. This stabilizing effect is attributed to the possibility of hydrogen bonding and dipole–dipole interaction in the water. The n→π* donation of N–C═S leads to a stronger interaction between sulfur heteroatom of I and fullerene. In contrast to the previous report on the produced thio-oxindoles in organic solvents, toluene was found to be the best solvent in terms of the highest yield and the shortest reaction time, in this case, adsorption takes place in water with no catalyst addition.

Here, we have focused on chemical reaction of I and C₂₀ to produce I_a complex via the optimized TSs in the gas phase, toluene, dichloromethane, methanol, acetonitrile, dimethyl sulfoxide and water, using DFT approach.