Absolute Electrochemiluminescence Quantum Efficiency of Au Nanoclusters by Means of a Spectroscopy Charge-Coupled Device Camera

Currently, the electrochemiluminescence (ECL) efficiency of a luminophore is evaluated by measuring the ratio of ECL intensity generated by a certain number of electrons injected. Then, this ratio is compared to that of the commercial luminophore, Ru(bpy)32+ under the same test conditions. However, the ECL intensity from a luminophore will be different on every instrumental setup due to wavelength-specific interaction of light with photodetectors. Also, previous absolute ECL techniques require multiple instruments, each of which has its own wavelength-specific light losses leading to complicated hardware and calculation requirements. Herein, this paper presents an absolute way to evaluate the ECL quantum efficiency (QE), permitting researchers to quickly compare ECL results and elucidate ECL mechanisms. The accuracy and precision of this new physical strategy is verified with the well-studied Ru(bpy)32+ to find an ECL QE of 0.64%. The strategy was then exemplified with Au250(SC2H4Ph)18 to represent a difficult spectroscopic challenge and this ECL QE was found to be 0.0062%. Finally, Ru(bpy)32+ ECL QE at different TPrA concentrations was evaluated to understand how the TPrA concentration affects the ECL QE of Ru(bpy)32+. Significant Ru(bpy)32+ ECL QE decreases were viewed from 3.2 x 10-3% at 6.25 mM TPrA to 6.5 x 10-6% at 200 mM TPrA likely due to high excited state quenching. Along with our previous publications on Au cluster ECL, discussed are factors influencing the ECL intensity such as the diffusion of electroactive molecules, the stability of radicals, the reactivity of excited states, and the analyte's reactivity. Profound variations were observed on this finding, which has large implications for past, current, and future relative ECL efficiencies also discussed in length.