Halogen Effect on the Photoluminescence of 1D Hybrid Lead Halide Perovskites with a Bipyridinium Cation

Organic–inorganic hybrid perovskites (OIHPs) have emerged as a prominent class of materials due to their diverse structures and tremendous potential in optics and electronics. Herein, we present two one-dimensional (1D) OIHPs, (C₂₂H₁₈N₂)(PbX₃)₂ (X = Cl or Br), in the form of single crystals and microcrystals that incorporate a bisprotonated bipyridinium compound as the organic cationic component. These two OIHPs possess a double-perovskite 1D chain structure, where the organic bipyridinium cations are linked to the perovskite octahedra through N–H···X hydrogen bonds. The chloride OIHP displays two emission bands that are attributed to the singlet free exciton of the organic moiety and the singlet self-trapped exciton (STE) of the perovskites, respectively. In contrast, the bromide analogue exhibits a single broad emission band originating from the triplet STE of the perovskites. Excitation wavelength and temperature-dependent photoluminescence studies provide insights into the distinct emission mechanisms of these two Pb-based OIHP materials.