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

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.