These metal ions can act as quenchers of fluorescence through photoinduced electron transfer (PET) or electronic energy energy transfer (EET) quenching process. Article A calix[4]arene based turn off/turn on molecular receptor fo...

Metalloporphyrins containing Cu(II) and Ni(II) metal ions typically do not exhibit fluorescence due to a phenomenon known as the "heavy atom effect". When a heavy atom is present near a fluorescent chromophore such as a porphyrin, it can facilitate non-radiative decay pathways through mechanisms such as intersystem crossing (ISC). Such processes favor the conversion of electronic excitation energy into vibrational energy or heat rather than fluorescence emission.