AIPE-active platinum(ii) complexes with tunable photophysical properties and their application in constructing thermosensitive probes used for intracellular temperature imaging

Aggregation-induced phosphorescent emission (AIPE) luminogens based on phosphorescent transition metal complexes have many application advantages in bioimaging compared with fluorescent organic dyes because of their long excitation lifetime and reduced photobleaching. Up to now, however, there are few reports about phosphorescent complexes with AIPE properties, and the reported mechanism of AIPE also needs to be studied in detail. Herein, two series of Pt(ii) complexes with different Schiff base ligand structures were designed and synthesized, and all these platinum complexes exhibited obvious AIPE properties. By introducing various electron-rich and electron-deficient functional groups into the Schiff base ligand, the relationship between the AIPE activity and ligand chemical structure was studied in detail. Based on this, a complex with 50% solid-state quantum efficiency has been obtained. Furthermore, one strategy to construct thermoprobes by combining this kind of AIPE-active complexes with a thermosensitive N-isopropylacrylamide hydrogel was proposed. The photophysical properties of the resultant thermoprobe were studied in detail in different physiological environments of varying pH, ions and amino acids, demonstrating their great stability and low cytotoxicity. Finally, the application of this kind of thermoprobe in intracellular temperature distribution imaging was demonstrated.