Fig. 2. Design and identification of Brønsted acid-unlocked iron ligand-to-metal charge transfer.

a In situ generating Brønsted acid and CF₃COO⁻. b Oxydibenzene as redox buffer. i Standard conditions: alkene (6, 0.2 mmol), (CF₃CO)₂O (1.0 mmol), Selectfluor (0.3 mmol), Fe(acac)₃ (0.02 mmol), oxydibenzene (0.1 mmol), isopropanol (0.4 mmol), and CH₃CN (0.1 M), N₂, blue LEDs, 12-h reaction time; (ii) without oxydibenzene under standard conditions; (iii) with oxydibenzene as redox buffer. c The advantage of balanced system. (i) standard conditions; (ii) without isopropanol under standard conditions; (iii) with TFA instead of TFAA and isopropanol in standard conditions. d Stoichiometric experiments of Fe(III)-intermediate species. TfOH trifluoromethanesulfonic acid, N.D. not detected. e UV–Vis experiments. f Light on/off experiments. g Kinetic studies of Fe(acac)₃.