This study is led by Prof. Zang (Green Catalysis Center and College of Chemistry, Zhengzhou University), and the research team proposed a new aggregation-induced emission mechanism for phosphorescent nanoclusters, that is, aggregation-induced barrier to oxygen (AIBO).
In their AIE study of phosphorescent trinuclear copper(I) nanoclusters protected by the alkyne ligands, the researchers found that when irradiated dimethyl sulfoxide (DMSO) stock solution containing metal clusters with ultraviolet lamp, a rapid phosphorescent switching effects was observed (see the video below). Interestingly, the emission wavelength after irradiation was very similar to those of the crystalline state and the aggregated state in the water, indicating that the emission mechanism in the solution was the same as that in solid states. “Some other factors must be existence to affect the AIE property of phosphorescent clusters” Prof. Zang says.
As we know, triplet oxygen in solvents quench phosphorescence and can be activated by UV light irradiation to form singlet oxygen in the presence of a photosensitizer. Meanwhile, metal clusters usually exhibit good photosensitive properties. Thus, a possible mechanism for the photo-response property of the metal clusters was proposed and confirmed by experiments: Phosphorescence of the metal clusters is quenched by oxygen molecules without UV light irradiation. Upon UV light irradiation, the oxygen molecules are converted to singlet oxygen due to the photosensitive property of the metal clusters. The produced singlet oxygen reacts with sulfoxide molecules and is depleted, enhancing the phosphorescence of the metal clusters.
Furthermore, the research team proposed a new AIE mechanism for phosphorescent clusters, namely, aggregation-induced barrier to oxygen (AIBO): When in the solution dispersion state, the phosphorescence of the cluster is quenched by dissolved oxygen in the solvent; however, when the aggregate is formed, the oxygen and cluster are isolated, making the cluster shows strong phosphorescence-emitting properties (see the diagram below). The new mechanism is also validated by dispersing cluster samples in porous silica gel, which demonstrating a super-sensitive sensing effect on oxygen.
This work not only reports a series of AIE copper (I) clusters, enriching their various applications, but more importantly, proposes a new AIE mechanism and provided a new perspective to understand the influence of aggregation on the phosphorescence properties of molecules.
See the article:
Aggregation-induced barrier to oxygen (AIBO) - A new AIE mechanism for metal cluster with phosphorescence
National Science Review