From 498 to 1300 nm: The exceptional large emission shift of a cycloplatinated(II) complex caused by molecular aggregation

A new cycloplatinated(II) complex with ppy and 4-bromopyridine-2-carboxylic acid ligands was synthesized. Six kinds of pseudopolymorphs of 1 with different aggregated degrees were isolated including yellow-green 1·CH2Cl2, orange 1Y, red 1·½(CH3OH), brown 1B, dark-brown 1DB, and black 1·CHCl3 with their emission peaked at 498 and 529 nm, 615 nm, 676 nm, 712 nm, 893 nm, and 1300 nm, respectively. Among them, the luminescence of 1·CHCl3 peaked at 1300 nm is the longest emission wavelength of the reported platinum(II) complexes with similar structure. Systematic studies on their crystal structures, photophysical properties, and thermo-stability demonstrated that 1·½(CH3OH), 1B, 1DB, and 1·CHCl3 stack in the dimer, quasi-tetramer, multi-molecular aggregation and 1D “Pt(II) wire” structure based on intermolecular Pt–Pt interaction. Interestingly, the changes in color and in emission energy of pseudopolymorphs are completely consistent with their aggregated degrees. Furthermore, the molecular aggregation of 1 can be reasonably regulated by vapor absorption and heating. Any two aggregates can be transformed into each other except for 1Y. Interconversion between 1·CH2Cl2 and 1·CHCl3 results in an emission wavelength shift of 802 nm. To the best of our knowledge, this is the largest emission wavelength shift of cycloplatinated complexes based on ppy derivative caused by molecular aggregation. [Display omitted] •Six kinds of pseudopolymorphs of 1 with different aggregated degrees were isolated.•1·CHCl3 emits a long wavelength NIR luminescence peaked at 1300 nm.•The aggregates of 1 can be regulated by absorption of VOC vapor or heating.•The largest emission shift of Pt(II) complex was caused by molecular aggregation.