Transient Exciplex Formation Electron Transfer Mechanism

Figure 2

Schematic plot of free energy along the reaction pathway (A* + D ⇄ A*⋯D (loose pair of reactants) ⇄ A^-z D^+z (transition state or exciplex) ⇄ A^•-⋯D^•+ (solvent separated ion pair) ⇄ A^•- + D^•+) blue line—for long-range mechanism ((2), 𝜆=2.0 eV, Δ𝐺^‡_ET=0.5 eV); and red line—for transient exciplex mechanism (Δ𝐺_Ex^∗=−0.15 eV) for isoenergetic ET reaction (Δ𝐺_ET^∗=0) in butyronitrile (Δ𝐺^‡_Diff=0.14 eV). Experimental data on Δ𝐺^‡1, Δ𝐺_Ex^∗, Δ𝐺^‡_Ex along the reaction coordinate: green squares—for 9-cyanoanthracene* + 1, 8-dimethylnaphthalene in MeCN (Δ𝐺_ET^∗=−0.1 eV); dark cyan rhombs—in PrCN (Δ𝐺_ET^∗=0.01 eV); magenta triangles—for 9-cyanophenanthrene + 1, 2-dimethoxylbenzene in PrCN (Δ𝐺_ET^∗=0.1 eV) [15]; black circles—for 1, 2, 4, 5-tetracyanobenzene* + durene in 1, 2-dichloroetane (according to the experimental data [27, 28], Δ𝐺_ET^∗≈−0.5 eV).