Halide Replacement Effect on Proton Conductivity and Vapochromic Luminescence of Pt(II) Complexes

Abstract

Abstract A new vapochromic, proton-conductive Pt(II) complex, [PtBr(tpypyH)]Br2 ([1Br-H]Br, tpypy = 2,2′: 6′,2′′-terpyridine-4′,4′′′-pyridine) was synthesized to improve the proton conductivity and thermal stability of the Cl− analogue, [PtCl(tpypyH)]Cl2 ([1Cl-H]Cl). The effects of halide replacement on the photophysical properties of the complex differed in the solution and solid states; the metal-to-ligand charge transfer (MLCT) absorption band of [1Br-H]Br in the solution state appeared at a longer wavelength than that of [1Cl-H]Cl owing to the stronger π-donation of Br−. In contrast, the metal-metal-to-ligand charge transfer (MMLCT) emission of [1Br-H]Br appeared at a shorter wavelength than that of [1Cl-H]Cl, which is consistent with the longer Pt⋯Pt stacking distance in [1Br-H]Br. [1Br-H]Br exhibited relative humidity-dependent proton conductivity and water vapor induced vapochromic luminescence; the conductivity was comparably higher than that of [1Cl-H]Cl, but slightly lower in the high relative humidity (RH) region above 80%, likely due to the lower hydration number of [1Br-H]Br. HBr release from [1Br-H]Br occurred at a higher temperature than HCl release from [1Cl-H]Cl, suggesting the superior thermal stability of the HBr adduct. This study demonstrates the crucial role of halide anions in attenuating both the vapochromic and proton conduction behavior of Pt(II) complexes.