Reblooming of the cis-Bis(2-phenylpyridine) Platinum(II) Complex: Synthesis Updating, Aggregation-Induced Emission, Electroluminescence, and Cell Imaging

Studies on the syntheses, photophysical properties, and applications of cis-bis(2-phenylpyridine) platinum(II) complex (Pt(ppy)2) family are of great importance, but very limited progress has been achieved to date. Herein, a one-pot method was established for the syntheses of Pt(ppy)2-type complexes Pt-ppy and Pt-tBu. These two compounds were nonemissive in dilute solutions. However, they produced intense red and deep-red phosphorescence in the aggregation and film states, with lifetimes and quantum yields up to 1.92 μs and 70%, respectively, exhibiting unique aggregation-induced emission (AIE) characteristics. According to the experimental and theoretical studies, molecular configuration transformation (MCT) in the excited state may occur because of the d–d transition from the Pt center, causing nonradiative transitions in the solution. Nevertheless, the MCT would be largely restricted by the intermolecular interactions or rigid matrix, thereby enabling efficient phosphorescence in the aggregation state and in the PMMA films. Consequently, the AIE characteristics of Pt-ppy and Pt-tBu probably result from the restriction of molecular configuration transformation (RMCT). Due to the π–π and/or weak Pt–Pt interactions and the concentration-dependent emission characteristics, they emit deep-red and NIR emissions generated by excimer and/or MMLCT emitting species. Inspired by their AIE features, electroluminescence and cell imaging applications are explored. To the best of our knowledge, this is the first comprehensive study on the synthesis optimization, photophysical properties, AIE characteristics, and applications of the Pt(ppy)2-type complexes, which may rebloom the research studies on this type of Pt(II) complex family and provide valuable insights on the development of phosphorescent AIE metal–organic complexes.