Tailoring the photoluminescence of AIE-type gold nanoclusters <i>via</i> biomineralization-inspired polymorphism

Tailoring the aggregation-induced emission (AIE) characteristics of well-defined metal nanoclusters (MNCs) is highly sought after for numerous practical applications. Studies have primarily focused on assembling AIE-type MNCs using monomorphic molecules. Achieving polymorphic assemblies, with different molecular arrangements could provide valuable insights into the role of external molecular matrices on the photoluminescence (PL) behaviour of these NCs. In this study, by mimicking biomineralization, we successfully embedded AIE-type Au₂₂SG₁₈ NCs within different polymorphic environments of CaCO₃. Upon incorporation into CaCO₃ matrices such as, calcite, vaterite and a mixture of both, the PL was enhanced in all the inorganic composites accompanied by a significant blue shift. In the metastable vaterite matrix, Au₂₂SG₁₈ NCs exhibited the highest blue shift in the PL spectrum while in the stable crystalline matrix of calcite, the NCs showed the highest PL intensity as well as excited state lifetime. Time-resolved spectroscopic and single-molecule Raman studies revealed that variations in the PL of NCs are linked to the stability of their polymorphic structures, progressing from vaterite to a vaterite/calcite mixture, and finally to calcite. These findings shed light on the crucial role of external molecular arrangement in the AIE behaviour of MNCs.