Thermo‐ and Mechano‐Triggered Luminescence ON/OFF Switching by Supercooled Liquid/Crystal Transition of Platinum(II) Complex Thin Films

Abstract Trihexyltetradecylphosphonium (P_6,6,6,14) salts of luminescent anionic Pt(II) complexes, (P_6,6,6,14)[PtX₂(ppy)] (X = Cl^‐, Br^‐; ppy = 2‐phenylpyridinate), are synthesized and photofunctional thin films with crystal/liquid bi‐stability are fabricated. In particular, the chloride complex provides a thin film exhibiting thermo‐ and mechano‐triggered luminescence ON/OFF switching at ambient temperature, which is based on the control of the supercooled liquid phase and bright luminescent crystalline phase. The photophysical properties of the complexes are investigated and compared with those of the bromide complex and tetra(n‐butyl)ammonium salts of the complexes. Furthermore, detailed photophysical analysis reveals a large contribution of the charge‐transfer character to the ligand‐centered ³π π* excited state, which results in intense phosphorescence in the crystal and high‐contrast luminescence ON/OFF by the phase transition of the chloride complex.