Previous reports on Au13 clusters, such as Au13(dppe)5(EPTpy)2 and transition metal ions (Ni 2+ , Co 2+ , Cu 2+ ), have shown that the luminescence intensity of Au13 decreases upon complexation. This phenomenon is believed to be due to the energy transfer from the excited state of Au13 to the transition metal ion. In our study of the complexation between 21 and Fe 2+ , the MLCT transition of [Fe(Tpy)2] 2+ was observed in the long-wavelength region, but there was no significant overlap with the Au13 emission spectrum in that absorption wavelength region (Fig. ). Therefore, the quenching observed upon Fe 2+ complexation of 21 is likely due to photoinduced charge transfer, rather than Förster-type resonance energy transfer. Our present study reveals that [Fe(Tpy)2] 2+ can act as a charge transfer quencher for Au13 luminescence. However, as mentioned earlier, 20 is not quenched by the coexisting complex component (21)2Fe dimer.