Multi-Stimuli-Responsive Luminescent Switching Properties of Cycloplatinated(Ii) Complexes Bearing 2-Phenylpyridine Derivatives

Abstract

Three new cycloplatinated(II) complexes, Pt(ppy)L (1), Pt[(CF3)ppy]L (2) and Pt[dF(CF3)ppy]L (3) based on 2-phenylpyridine (ppy), 2-phenyl-5-(trifluoromethyl)pyridine [(CF3)ppy], 2-(2,4-Difluorophenyl)-5-(trifluoromethyl)pyridine [dF(CF3)ppy] and 4-[2-(4-fluorophenyl)ethynyl]-2-pyridinecarboxylic acid (L) ligands were synthesized and characterized. Complex 1 has one metastable structure and exhibits reversible mechanoluminescent property. On the contrary, each complex 2 and 3 has five types of metastable structures and exhibits multi-stimuli-responsive luminescent switching properties triggered by VOC vapors absorption, heating, and mechanical grinding. Moreover, complexes 2 and 3 display a series of untraditional luminescent switching behaviors such as two-step conversion processes, irreversible process and more than one thermally stable products. Systematic studies on crystal structure, luminescence spectra, PXRD and DFT theoretical calculation demonstrate that the luminescent switching properties of these complexes are attributed to the formation/elimination of intermolecular Pt-Pt interactions during structural conversion processes between metastable structures, which lead to the transformation of the lowest energy excited states between MLCT and MMLCT transitions. Furthermore, the unconventional luminescent switching behaviors are due to the strong stability of the metastable structures. In addition, the studies also reveal that the stacking structure of complex can affect its luminescent switching behavior, while the good molecular planarity of the complex is not conducive to the luminescent switching properties.

Keywords: cycloplatinated(II) complex, multi-stimuli-responsive luminescent switching properties, two-step conversion processes, irreversible conversion, intermolecular Pt-Pt interaction