Phosphorescent Square-Planar Platinum(II) Complexes of 1,3-Bis(2-pyridylimino)isoindoline with a Monodentate Strong-Field Ligand

摘要

A series of platinum(II) complexes bearing 1,3-bis(2-pyridylimino) isoindoline (BPI) derivatives as ligand have been prepared by substitution of the coordinated Cl in precursors [Pt(L)Cl] [L = L1 (1), L2 (2), L3 (3)] by a monodentate strongfield ligand such as CN~-, CN-cyclohexyl, PPh_3, NCS~-, PhS~-, or N(CN)_2~-. Most of these compounds display orange-to-red luminescence in both the solid state and solution at ambient temperature. Compared with precursors 1-3, both low-energy absorption and emission bands in ligand-substituted platinum(II) complexes 4-13 exhibit distinct blueshifts. The emission of platinum(II) complexes with CN-containing monodentate ligands shows progressive blueshifts with increasing ligand field strength: 609 (10, NCS-)→603 [12, N(CN)_2~-]→590 (4, CN-)→581 nm (7, C≡N-cyclohexyl). The emission of complexes 4-9 originates mainly from the ~3[π→π*(BPI)] ~3IL triplet excited state, mixed with some ~3[dπ(Pt)→π*(BPI)] ~3MLCT character. In contrast, the emission of 10-13 arises from a clearly increased ~3[π(L)→π*(BPI)] 3LLCT state with reduced ~3[π→π*(BPI)] ~3IL and ~3[5d(Pt)→π*(BPI)] 3MLCT character. Noticeably, dicyanamido-linked dinuclear complex 13 displays a significant ligand-ligand electronic interaction between the two BPI across the Pt-N≡C-N-C≡N-Pt bridge with remarkable LLCT character from one BPI to the other.