An Mn ²⁺ -based organic–inorganic hybrid with spatially separated charge transfer for efficient green phosphorescence

A novel manganese(II)-based organic–inorganic hybrid material, bis[(cyanomethyl)triphenylphosphonium] tetrachloridomanganate(II), (C 20 H 17 NP) 2 [MnCl 4 ] or [CTP] 2 [MnCl 4 ], has been synthesized and structurally characterized. The compound crystallizes in the monoclinic space group P 2 1 / n , with its three-dimensional packing stabilized by a network of weak intermolecular forces, primarily C—H...Cl hydrogen bonds and van der Waals interactions. Under UV excitation, the material exhibits an intense green photoluminescence centred at 520 nm, characteristic of the spin-forbidden 4 T 1 (G)→ 6 A 1 (S) transition of the tetrahedrally coordinated Mn 2+ ion. Transient decay analysis confirms its phosphorescent nature, revealing a remarkably long lifetime of 2.92 ms. Periodic density functional theory (DFT) calculations reveal a direct band gap of 1.94 eV and, critically, a spatially separated electronic structure where the highest occupied crystalline orbital is localized exclusively on the inorganic [MnCl 4 ] 2− anion and the lowest unoccupied orbital resides solely on the organic [CTP] + cation. This clear spatial separation defines the primary photoexcitation as an inter-ionic charge transfer from the anion to the cation, which effectively suppresses nonradiative recombination pathways and is identified as the key factor enabling the observed long-lived phosphorescence. This study not only reports a new efficient green phosphor based on an earth-abundant metal, but also demonstrates that engineering a spatially segregated charge-transfer state is a viable strategy for achieving persistent luminescence in hybrid materials.