Synthesis, structure and luminescent switching properties of cycloplatinated(II) complexes bearing phenyl β-diketone ligands

Abstract

Nine cycloplatinated(II) complexes (Pt1-Pt9) bearing 2-phenylpyridine (ppyH) derivatives and phenyl β-diketone (L1H = 1-phenyl-1,3-butanedione; L2H = 1,3-diphenyl-1,3-propanedione; L3H = 3-phenyl-2,4-pentanedione) ligands were designed and synthesized. All complexes except Pt2 exhibited reversible mechanoluminescence property. In addition, the complexes (Pt3, Pt6, and Pt9) containing L3 ligand also displayed concentration-dependent luminescence switching property in CH2Cl2 solution. With the concentration of CH2Cl2 solution of such complexes increasing, their luminescence changed from original cyan or cyan-green to the broad red luminescence with the emission redshifts exceeding 230 nm. Systematic studies on crystal structure, luminescence spectra and PXRD demonstrate that the structures of phenyl β-diketone ligands and the planarity of complexes seriously affect the luminescent switching properties of the complexes. The reversible mechanoluminescence property and the concentration-dependent luminescence switching property are most likely due to the change of the energy of the metal-to-ligand charge transfer (MLCT) transition and/or conversion of the lowest energy excited states from MLCT to metal-metal-to-ligand charge transfer (MMLCT) transitions caused by the formation of aromatic π-π stacking interaction and/or intermolecular Pt···Pt interaction.