Observation of Room-Temperature Deep-Red/Near-IR Phosphorescence of Pyrene with Cycloplatinated Complexes: An Experimental and Theoretical Study

Pyrene-containing cyclometallated Pt-II complexes, with the pyrene moiety directly cyclometallated (Pt-1) or connected to a 2-phenylpyridine (ppy) ligand through a C-C (Pt-2) or C C bond (Pt-3), and a control complex with a phenyl group attached to the ppy ligand (Pt-4) have been prepared. Room-temperature deep-red/near-IR (NW) phosphorescence emission (650-800 nm) was observed for Pt-1, Pt-2 and Pt-3, whereas Pt-4 showed emission at 528 nm. We found that Pt-2, in which the pyrene moiety is not directly cyclometallated, shows intense pyrene-based phosphorescence, which contrasts with a previous report that direct cyclometallation is necessary for the observation of the phosphorescence of pyrene in cyclometallated complexes. Besides the phosphorescence emission in the deep-red/near-IR range, a fluorescence emission band at higher energy was observed. Thus, these complexes can be described as unichromophore multi-emissive materials. Normal (MLCT)-M-3/(IL)-I-3 emission at 528 nm was observed for Pt-4. The UV/Vis absorption and phosphorescence emissions of the complexes were rationalized by DFT/TDDFT calculations. Theoretical calculations propose pyrene-localized T-1 states ((IL)-I-3) for Pt-1, Pt-2 and Pt-3, which is supported by the experimental results. The complexes were used in luminescent O-2-sensing experiments. These studies will be helpful in the development of room-temperature phosphorescent materials and their application as luminescent molecular sensing or electroluminescent materials are promising.