Efficient Solid‐State Emission Control by Positional Isomerism for Platinum(II) Complex with Donor–π–Acceptor Ligand

Square‐planar platinum (Pt)(II) complexes have attracted considerable attention owing to their unique luminescent properties, and the development of facile methods to control them is very important. A series of Pt(II) complexes containing a donor–π–acceptor (D–π–A) isomer ligand (ortho‐, meta‐, and para‐position; Pt‐O, Pt‐M, and Pt‐P) is prepared to investigate the positional isomerism on the Pt(II) complex. In particular, the metal‐to‐ligand charge transfer and ligand intramolecular charge transfer characteristics are examined depending on the positional isomer and compared with the donor‐free Pt(II) complex. All Pt(II) complexes observe slightly red‐shifted emission within 10 nm in the order of Pt‐O < Pt‐M < Pt‐P. Experimental data and theoretical calculations show that the Pt(II) complex lowest unoccupied molecular orbital energy level is controlled systematically by the donor position dependency. In particular, the small perturbation of the electronic state by positional isomerism in the single molecule induces significant phosphorescence color disparities of more than 82 nm in the solid‐state emission spectra and aggregation‐induced emission. The intriguing phosphorescent behavior is explained by the ligand‐dependent macroscopic molecular array with the Hirshfeld analysis. Consequentially, this paper reports a facile emission control method by the D–π–A ligand positional isomerism in the Pt(II) complex. This work provides a donor–π–acceptor ligand positional isomerism strategy that can efficiently control the phosphorescence properties of square‐planar platinum(II) complexes up to the single‐molecular and multi‐molecular levels. Their intriguing multi‐molecular photoluminescence properties in the solid‐state are explained by the ligand‐dependent macroscopic molecular array.