Excitation dependent white and red-NIR emission of a MnII-based complex

Abstract

Nowadays, organic and organic–inorganic supramolecular crystals are potential candidates for lighting applications. In this work, a new molecular crystal (C₅H₈N₃)₂[MnCl₄(C₅H₇N₃)₂] abbreviated (AmpH)₂[MnCl₄(Amp)₂], (C₅H₇N₃ = Amp = 2-amino-4-methylpyrimidine), containing octahedral Mn(II) complex [MnCl₄(C₅H₇N₃)₂]²⁻ and 2-amino-4-methylpyrimidinium cation [C₅H₈N₃]⁺ has been successfully investigated. The thermal analysis of the synthesized compound shows that it is thermally stable up to 190 °C. The absorption analysis demonstrates an intense absorption band in the UV region with no characteristic absorption in the visible range which makes the material suitable for optoelectronic application. The direct and indirect investigated gap energies are found to be 3.66 and 3.51 eV, respectively, and that proves the semiconducting property of the investigated compound. The solid-state photoluminescence measurements allowed the identification of a broad cold white-light emission under an excitation wavelength of 250 nm. Under an excitation wavelength of 350 nm, the material exhibits an emission centered at around 644 nm assigned to the red phosphorescence emission from the triplet state characteristic of the octahedral Mn^II ions. In addition, a broad NIR-emission band is observed between 700 and 900 nm. Hence, the emission from (AmpH)₂[MnCl₄(Amp)₂] can be varied from white to red-NIR by simple variation of excitation wavelengths. Then the obtained material is suitable for lighting applications such as organic light emitting diodes (OLEDs) and is bio-compatible for bio-sensing and bio-imaging as a heavy atom free material.