Crystallization induces thermally activated delayed fluorescence of Ag14 nanocluster

Abstract

Studying the differences in the excitonic dynamic processes between the dispersed state and crystalline state is important for understanding crystallization-induced emission enhancement (CIEE). In this work, we characterized the photophysical processes of Ag14 nanocluster in both solution and crystalline state using photoluminescence spectra combined with transient absorption spectra. The nanocluster exhibits fluorescence (Fl)-phosphorescence (Ph) co-dominant emission in solution, while thermally activated delayed fluorescence (TADF) is observed in the crystals. From solution to crystals, the photoluminescence quantum yield (PLQY) of the cluster improves from below 0.1% to 33% due to the triggering of TADF combined with the restriction of intramolecular motion (RIM) and the aggregation-induced barrier to oxygen (AIBO). A detailed photophysical study reveals that the TADF is a property of organized cluster assemblies and does not occur in the cluster monomers. We reveal that the key to the TADF of crystalline Ag14-dcbdt lies in inter-cluster electron orbital coupling, which decreases the singlet-triplet splitting energy. These findings provide new insights into the CIEE of cluster-based aggregates and can be used to guide the synthesis of high-performance cluster-based luminescent materials.