Pt(II) Complexes Showing Multicolor Emissions from Nanoparticles in Solution and Reversible Grinding- and Heating-Induced Luminescence Switching in Solid State

Abstract

To well understand luminescence modulation of Pt(II) complexes by inter-molecular interactions, three platinum complexes [Pt(moppy)Cl(L)] have been synthesized (Scheme 1) through incorporating the same C^N ligand moppyH=2-(4-methoxyphenyl)pyridine, while different auxillary ligands L: SEt₂ in 1, iccy=isocyanocyclohexane in 2, and icna=isocyanonaphthalene in 3. Crystal structures indicate that neighbouring molecules are connected through π⋅⋅⋅π interactions, forming supramolecular dimer structures in both 1 and 2, while supramolecular chain structure in 3. In a CH₃CN-H₂O mixed solvent, complexes 1–3 reveal enhanced luminescence due to nanoparticle formation. Upon increasing water fraction from 0 % to 90 %, complex 1 exhibits increasing green luminescence with two broad emissions at 450 and 516 nm. In contrast, both 2 and 3 show multicolour emissions, transiting from blue to yellow-green for 2, and from blue green to orange red for 3. Moreover, complex 3 exhibits reversible luminescence switching between on state with orange-red emission and off state upon alternately grinding and heating. In this paper, we discuss the influences of molecular structures and inter-molecular π⋅⋅⋅π and Pt−Pt interactions on luminescence behaviours of complexes 1–3.