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

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Abstract

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 strong-field ligand such as CN, CN-cyclohexyl, PPh3, 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 13, both low-energy absorption and emission bands in ligand-substituted platinum(II) complexes 413 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 49 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 1013 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.

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