Structural\nChanges and Differences in Intrinsic Photoluminescence\nof Four Cationic Two-Dimensional Lead Halide Frameworks Modulated\nby Synthesis Temperature

Luminescent\nhybrid organolead halide materials with cationic inorganic\nframeworks and high chemical inertness have demonstrated broad application\nprospects in the visible light region. However, the corresponding\nrelationship between structural changes and luminescence properties\nin such materials needs further clarification. Here, for the first\ntime, we have successfully synthesized [Pb<sub>2</sub>X<sub>3</sub>](PDAH)(H<sub>2</sub>O) (X = Cl or Br, PDAH = C<sub>7</sub>H<sub>4</sub>NO<sub>4</sub>) single crystals via a facile hydrothermal\nmethod and then obtained [Pb<sub>11</sub>X<sub>14</sub>](PDA)<sub>4</sub> (X = Cl or Br, PDA = C<sub>7</sub>H<sub>3</sub>NO<sub>4</sub>) at higher temperatures. The different synthesis temperatures resulted\nin significant differences in the luminescence properties of the two\ngroups of structures. X-ray crystallography revealed the different\ndegrees of distortion of the Pb<sup>II</sup> centers’ coordination\nenvironment between the two structures, which would significantly\naffect the electron–phonon coupling process under excited states\nand ultimately affect the emission properties originating from self-trapped\nexcitons (STEs) of the two materials. In addition, density functional\ntheory (DFT) calculations indicate that the two structures have different\nband gap characteristics due to the different proportions of inorganic\nand organic components, which also affect the optoelectronic properties\nof the two groups of materials. It is also worth mentioning that the\nbroadband orange-light emission of [Pb<sub>11</sub>Br<sub>14</sub>](PDA)<sub>4</sub> with a high photoluminescence quantum efficiency\n(PLQE) of 86% endows it with potential applications in WLEDs.