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.