Mechanochemical synthesis of one-dimensional (1D) hybrid perovskites incorporating polycyclic aromatic spacers: highly fluorescent cation-based materials

Abstract

Three polycyclic aromatic cations, 2-ammonium fluorene (AF), 2-ammonium anthracene (AA) and 2,7-diammonium fluorene (DAF) are successfully assembled with inorganic PbBr₆ octahedra to synthesize (AF/AA)₂PbBr₄ and (DAF)PbBr₄ one-dimensional (1D) hybrid perovskites. The synthesis of the perovskites is performed via an environmentally-friendly mechanochemical approach involving a solid-state solventless reaction. The analysis of the X-ray powder diffraction (XRD) data revealed that the crystal structure of these materials consisted of quasi-linear wires of PbBr₄²⁻ separated by polycyclic cations with alternating positions of NH₃⁺ groups. DFT calculations have shown a remarkable contribution of the orbitals of 2-ammonium fluorene to both the valence band maximum (VBM) and conduction band minimum (CBM) of the (AF)₂PbBr₄ structure. Moreover, the same hybrid materials were effectively prepared as thin films by using the spin-coating method from a solution containing the precursors. Although these hybrid perovskites are not intrinsically emissive, the strong fluorescence signal from the organic cation is preserved.