General procedure for NMR studies. To a flame-dried 10 mL Schlenk flask, complex 1 (0.00137 mmol, 1 eq.), benzophenone (0.002 mmol, 1.5 eq.), styrene (0.0068 mmol, 10 eq.) and benzene (2 µL) as internal standard were dissolved in CD2Cl2 (0.5 mL). The dark red solution was freeze-pump-thawed and transferred to a J-young NMR tube after filtration. The tube was kept under dark conditions until the NMR measurements were performed. All NMR samples were irradiated with a 390-500 nm light source via a light probe attached to the bottom of the NMR machine. To determine the concentration of complex 1, signals at -3.16 (1H) and 1.82 (6H) ppm were integrated. To determine the concentration of [Co II (TPP)], signals at 9.62 (12H) and 12.85 (8H) ppm were integrated.