In Situ Synthesis of Highly Emissive Manganese Halides with Modified Bisphosphonium Cations toward Information Encryption

Multisite modulation for organic–inorganic hybrid metal halides (OIMHs) plays an important role in the optimization of their photophysical performance. Herein, we proposed an organic cation modification strategy on the phosphorus sites based on 1,2-Bis(diphenylphosphino)ethane (DPPE) by a simple one-pot solvothermal method. Three zero-dimensional (0D) manganese-based OIMHs, two novel MdppeMnCl 4 ·H 2 O and EdppeMnCl 4, as well as the byproduct [Mn(dppeO 2 ) 3 ][MnCl 4 ] were obtained (Mdppe = methyl-coordinated with DPPE; Edppe = ethyl-coordinated with DPPE; and dppeO 2 is obtained by oxidation of DPPE). All the samples possess the four-coordinated [MnCl 4 ] 2– polyhedron, while [Mn(dppeO 2 ) 3 ][MnCl 4 ] contains another six-coordinated cation [Mn(dppeO 2 ) 3 ] 2+ complex. According to the relevant optical measurements, MdppeMnCl 4 ·H 2 O and EdppeMnCl 4 both show bright green emissions with photoluminescence quantum yields of 55.66% and 80.42%, respectively. By contrast, [Mn(dppeO 2 ) 3 ][MnCl 4 ] shows an orange emission that is confirmed to be associated with six-coordinated Mn 2+ ions by temperature-dependent PL spectra. Based on the good stability and solution processability of EdppeMnCl 4, a luminescent ink was developed and shows potential application in display and information encryption fields. The unique cation modification strategy in this work opens up the ways for designing and developing novel OIMHs and extends the application prospects of manganese-based halides.