Synthesis, structure and tri-stimuli-responsive luminescent switching properties of a bis(-acetylide) platinum(II) complex

A square-planar bis(sigma-acetylide) platinum(II) complex, Pt(PhenC--CTES)(C--C-C6H4-2-Cl)2 (1) (PhenC--CTES = 3-(2-triethylsilylethynyl)-1,10-phenanthroline) was synthesized. Three species with different stacking structures, including two solvated yellow-green samples 1 & sdot;Cl2CHCHCl2 and 1 & sdot;ClCH2CH2Cl, and one red solvent-free species 1, were obtained by exposure 1 into the different VOC vapors. 1 & sdot;Cl2CHCHCl2 and 1 & sdot;ClCH2CH2Cl emit a green luminescence peaked at 513 (548, sh) nm and 545 (517, sh) nm, respectively and exhibit the vapor-, thermo-, and mechanical grinding triggered tri-stimuli-responsive luminescent switching properties. Once exposure to CH2Cl2 vapor or heating at 110 degrees C, both 1 & sdot;Cl2CHCHCl2 and 1 & sdot;ClCH2CH2Cl will lose their solvated molecule and converted to the red solvent-free species 1. Upon mechanical grinding, 1 & sdot;Cl2CHCHCl2 and 1 & sdot;ClCH2CH2Cl will be changed to an amorphous species 1G with red color and red luminescence peaked at 675 nm. Meanwhile, the heating and ground samples could be converted back to the original crystalline 1 & sdot;Cl2CHCHCl2 and 1 & sdot;ClCH2CH2Cl by absorbing Cl2CHCHCl2 or ClCH2CH2Cl vapor. Systematic studies on the crystal structure, luminescence spectrum, PXRD patterns as well as TD-DFT calculations demonstrate that the mechanism of the reversible tri-stimuli-responsive luminescent switching properties of complex 1 is due to the interconversion of the lowest-energy excited states of metastable species between ligand to ligand/metal to ligand charge transfer (LLCT/MLCT) and ligand to ligand/metal-metal to ligand charge transfer (LLCT/MMLCT) caused by the formation/destruction of intermolecular Pt-Pt interactions and/or aromatic pi-pi stacking interactions under external stimuli.