Structural Changes and Differences in Intrinsic Photoluminescence of Four Cationic Two-Dimensional Lead Halide Frameworks Modulated by Synthesis Temperature

Luminescent hybrid organolead halide materials with cationic inorganic frameworks and high chemical inertness have demonstrated broad application prospects in the visible light region. However, the corresponding relationship between structural changes and luminescence properties in such materials needs further clarification. Here, for the first time, we have successfully synthesized [Pb₂X₃](PDAH)(H₂O) (X = Cl or Br, PDAH = C₇H₄NO₄) single crystals via a facile hydrothermal method and then obtained [Pb₁₁X₁₄](PDA)₄ (X = Cl or Br, PDA = C₇H₃NO₄) at higher temperatures. The different synthesis temperatures resulted in significant differences in the luminescence properties of the two groups of structures. X-ray crystallography revealed the different degrees of distortion of the Pb^II centers' coordination environment between the two structures, which would significantly affect the electron-phonon coupling process under excited states and ultimately affect the emission properties originating from self-trapped excitons (STEs) of the two materials. In addition, density functional theory (DFT) calculations indicate that the two structures have different band gap characteristics due to the different proportions of inorganic and organic components, which also affect the optoelectronic properties of the two groups of materials. It is also worth mentioning that the broadband orange-light emission of [Pb₁₁Br₁₄](PDA)₄ with a high photoluminescence quantum efficiency (PLQE) of 86% endows it with potential applications in WLEDs.