Mechanochromic luminescent property and anti-counterfeiting application of AIE-active cyclometalated platinum(II) complexes featuring a fused five-six-membered metallacycle

Two couples of pinene-containing (NC)-C-boolean AND*N and C*NDN-coordinated Pt(II) complexes featuring a fused five-six-membered metallacycle have been developed, and their structures were confirmed by NMR, MS and single crystal X-ray crystallography. Cyclometalated complex (-)-2 has two polymorphs involving yellow-orange form (-)-2 center dot CH3COCH3 and orange form (-)-2 center dot CH3SOCH3, revealing different conformations and intermolecular pi-pi interactions. Complexes (-)-1 and (-)-2 display prominent aggregation-induced emission (AIE) in THE-water solution system with emission quantum yield ('' em ) strengthening from 0.2% to 37%. Despite the structural similarity of complexes (-)-1 and (-)-2, different mechanochmmic luminescent phenomena have been distinguished. No detectable change in color and luminescence of yellow solids (-)-1 can be found during the grinding process, whereas yellow solids of complex (-)-2 show a reversible mechanochormic luminescent behavior and a simultaneous crystal-to-amorphous transformation. It is speculated that dimeric structures containing weak pi-pi interactions are formed under the mechanical force, and simultaneously the molecular conformation becomes more planar, improving the conjugation, inducing the emissive state variance with more (MLCT)-M-3/(ILCT)-I-3 character. Moreover, anti-counterfeiting application based on complex (-)-2 has been explored. This research provides a new design strategy for exploring AIE-active Pt(II) complexes with high-contrast mechanochromic luminescence.

Automated summary

This study developed pinene-containing Pt(II) complexes and confirmed their structures through experimental and characterization techniques. These complexes exhibited aggregation-induced emission in aqueous solution and showed different mechanochromic luminescent behaviors. The study also found that the structure and luminescent properties of the complexes can undergo reversible changes by applying mechanical force. Additionally, the possibility of applying these compounds in anti-counterfeiting applications was explored.