Mechanochromism and circularly polarized luminescence of chiral cyclometalated platinum(II) complexes with different configurations and aggregated forms

Abstract

Using a new synthesis method, we have prepared two different coordination configurations of chiral cyclometalated N^C^N-coordinated and C^N-coordinated Pt(II) complexes by controlling the Cl− source. Single-crystal X-ray diffraction determines the tridentate and bidentate structures. All N^C^N-coordinated and C^N-coordinated Pt(II) complexes emit green-yellow light in CH2Cl2 solutions. Square-planar N^C^N-Coordinated complexes (−)-1 and (−)-2 show remarkable aggregation-induced emission behaviors in mixed CH2Cl2/n-hexane solutions with the emission quantum yield (Φem) intensified significantly. In addition, the luminescent color could change from green-yellow to red by varying the volumetric fraction of n-hexane. Complex (−)-2 grafted with long alkyl chains could form helical stacking aggregates, inducing enhanced ECD signals and measurable CPL activity. The yellow and orange solids of complex (−)-1 can be separated, and a high-contrast mechanochromic luminescence is found for the yellow form. Furthermore, the potential utility has been attempted in anti-counterfeiting applications based on the yellow solid of (−)-1. This study provides a new design strategy for the preparation of chiral cyclometalated Pt(II) complexes with specific configurations and aggregated forms that have various optical and electronic properties.