The electrochemistry, near-infrared photoluminescence (NIR-PL) spectroscopy, and electrogenerated chemiluminescence (ECL) of Au 25 (SC 2 H 4 Ph) 18 + -C 6 F 5 CO 2 − (Au 25 + ) clusters were investigated. For the first time, NIR-ECL emission was observed in both annihilation and coreactant paths. Our newly developed spooling spectroscopy was employed during the ECL evolution and devolution processes along with explicit NIR-PL spectroscopy to elucidate light generation mechanisms. It was discovered that the electronic relaxation of the Au 25 − excited state to the ground state plays a key role in giving off ECL at 893 nm, while intermediate, strong, and weak NIR-PL emissions at 719/820, 857, and 1080 nm can be attributed to the excited states higher than the HOMO-LUMO gap, across the HOMO-LUMO gap, and of semirings, respectively. T he optical properties of nanostructures such as silicon nanocrystals (NCs), 1 carbon quantum dots, 2 and gold nanoparticles (NPs) 3 are attractive to many researchers because of their potential applications. 4 Among a variety of gold NPs, Au 25 L 18 clusters have been the focus of recent investigations due to their molecule-like (1.1 nm in diameter) behavior, monodispersed synthesis protocols, 5 and unique optical, 6 electrochemical, 7 and structural portfolio. 8 A Au 25 cluster consists of an icosahedral Au 13 core and six semi-rings containing -Au-S-Au-S-. 6g,9 Murray et al. 3 and Jin et al. 10 pioneered studies exploring the various properties of Au 25 , for instance, observing the difference in photoluminescence (PL) by changing the combination of protecting ligands and electropositivity. 11 These studies showed that the origins of the clusters' optical properties are dependent on the charge and protecting ligand's functionalities. 10a Zhu et al. and Chen et al. demonstrated that Au clusters protected by bovine serum albumin (BSA) can also be utilized in analytical detection methods based on spectroscopic properties of the Au-BSA cluster. 12 Of the stable charged states of Au 25 L 18 z (z = −1, 0, and +1), the −1 form is the most studied, although recent synthetic protocols have allowed the isolation and investigation of the 0 and +1 states. The different charged states induce various properties on the gold clusters that have been probed by 1 H NMR, 13 PL, 10a and electron paramagnetic resonance spectroscopy. 14 Electrogenerated chemiluminescence (ECL) is the process in which electrogenerated radicals form excited species emitting light without the need of an external light source. 15 Advantages of ECL include simultaneous generation of radical cations and anions and the control of electrode potentials that drive light emission processes. ECL has great potential in biological applications such as detection in immunoassays, food and water testing, trace metal determination, sensors, and biomolecules. 15 Our motivation is to explore ECL of various compounds 2b,c,16 toward applications in biosensors and bioanalytical chemistry.Herein, we report the ECL of Au 25 in the near-infrared (NI...