Observation of a new type of aggregation-induced emission in nanoclusters.

The strategy of aggregation-induced emission (AIE) has been widely used to enhance the photo-luminescence (PL) in the nanocluster (NC) research field. Most of the previous reports on aggregation-induced enhancement of fluorescence in NCs are induced by the restriction of intramolecular motion (RIM). In this work, a novel mechanism involving the restriction of the "dissociation-aggregation pattern" of ligands is presented using a Ag29(BDT)12(TPP)4 NC (BDT: 1,3-benzenedithiol; TPP: triphenylphosphine) as a model. By the addition of TPP into an N,N-dimethylformamide solution of Ag29(BDT)12(TPP)4, the PL intensity of the Ag29(BDT)12(TPP)4 NC could be significantly enhanced (13 times, quantum yield from 0.9% to 11.7%) due to the restricted TPP dissociation-aggregation process. This novel mechanism is further validated by a low-temperature PL study. Different from the significant PL enhancement of the Ag29(BDT)12(TPP)4 NC, the non-dissociative Pt1Ag28(S-Adm)18(TPP)4 NC (S-Adm: 1-adamantanethiol) exhibits a maintained PL intensity under the same TPP-addition conditions. Overall, this work presents a new mechanism for largely enhancing the PL of NCs via modulating the dissociation of ligands on the NC surface, which is totally different from the previously reported AIE phenomena in the NC field.