To gain mechanistic insights into the amidyl radical insertion reaction to BCBs, a series of experiments were carried out (Fig. ). UV-Vis absorption studies implied that only fac-Ir(ppy)3 exhibits efficient absorption at λmax = 450 nm (Fig. ). Stern-Volmer luminescence quenching studies further suggested that N-amidocollidinium tetrafluoroborate 2d is the sole quencher of the excited photocatalyst (Fig. ).