Crystallization induces thermally activated delayed fluorescence of Ag14 nanoclusters†

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 nanoclusters both in solution and in the crystalline state using photoluminescence spectra combined with transient absorption spectra. The nanoclusters exhibit 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 boosting of TADF combined with the restriction of intramolecular motion (RIM) and the aggregation-induced barrier to oxygen (AIBO). We reveal that the enhanced TADF of crystalline samples of Ag₁₄-dcbdt can be attributed to 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.