Probing Complex Photophysics in Gold Nanoclusters

We report striking photophysical behaviour of Au25(PET)18 (PET = 2-phenylethanethiol) nanoclusters in both anionic and neutral forms. Using broad spectral coverage and tuneable excitation, steady-state, and time-resolved measurements reveal low-energy absorption and emission features, weak photoluminescence, and multiexponential decay dynamics. Notably, the neutral species shows excitation-wavelength-dependent emissions and a pronounced mismatch between excitation and absorption spectra, violating Kasha's and Vavilov's rules. These results point towards complex excited-state behaviour of these systems and the crucial role of instrumentation design in their accurate characterisation.