Confined Structural Water Molecules as Alternative Potential Emitters for Bright Photoluminescence of Thiolate‐gold Complexes

The debate about water as an emitter has spanned nearly a century, but how it emits bright colors remains elusive. In this report, using the widely used Au(I)‐alkanethiolate complex (Au(I)‐SRs, R=−(CH₂)₁₂H) with AIE properties as a model system, by carefully manipulating the delicate surface‐ligand interactions at the nanoscale interface, together with a careful spectral investigation and an isotopic diagnostic experiment of heavy water (D₂O), we demonstrated that the structural water molecules (SWs) trapped in the nanoscale interface or space are the true emission centers of metal nanoclusters (NCs) and the aggregates of Au(I)‐SRs complexes, instead of a well‐organized metal core dominated by quantum confinement mechanics. Unlike conventional hydrogen‐bonded water molecules, due to interfacial adsorption or spatial confinement, the p‐orbitals of two O atoms in SWs can form strong electronic interactions through spatial overlap, thus constructing a set of interfacial states, one of which is characterized by π‐bonding, thus providing alternative channels (or paths) for the relaxation decay of the excited electrons. Using the one‐dimensional free‐electron gas model, the energy levels calculated by the Schrödinger equation are in perfect agreement with the experimental observations, further validating the SWs model.