Ligand Control of Room-Temperature Phosphorescence Violating Kasha’s Rule in Hybrid Organic–Inorganic Metal Halides

Two hybrid organic–inorganic metal halides with room-temperature phosphorescence (RTP) have been designed and synthesized. The aromatic organic ligands in the hybrid structures give rise to the phosphorescent property, while the rigid inorganic frameworks in the hybrid structures enhance the RTP efficiency. Pb2(PLA)(H2O)2Br2 (PLA, 1,4-phenylenediacetic acid) shows the anti-Kasha’s rule RTP, which has been rarely reported before. The twisted intramolecular charge transfer (TICT) in a flexible PLA ligand might be the origination of the anti-Kasha’s rule RTP according to the photoluminescence study under the variables of temperature, excitation wavelength, and ligands. A method that combined the calculations from Platon and CrystalExplorer has been built to analyze the packing mode and interaction of the ligands. The compact face-to-face packing of aromatic ligands leads to the highest RTP efficiency in Pb4(TPA)3Br2. Due to the strong covalent bonding, Pb4(TPA)3Br2 exhibits superior thermal stability and water resistance, which can serve as an efficient LED underwater.