Solvatochromic Photoluminescent Effects in All‐Inorganic Manganese(II)‐Based Perovskites by Highly Selective Solvent‐Induced Crystal‐to‐Crystal Phase Transformations

Abstract The development of lead‐free perovskite photoelectric materials has been an extensive focus in the recent years. Herein, a novel one‐dimensional (1D) lead‐free CsMnCl 3 (H 2 O) 2 single crystal is reported with solvatochromic photoluminescence properties. Interestingly, after contact with N,N‐dimethylacetamide (DMAC) or N,N‐dimethylformamide (DMF), the crystal structure can transform from 1D CsMnCl 3 (H 2 O) 2 to 0D Cs 3 MnCl 5 and finally transform into 0D Cs 2 MnCl 4 (H 2 O) 2 . The solvent‐induced crystal‐to‐crystal phase transformations are accompanied by loss and regaining of water of crystallization, leading to the change of the coordination number of Mn 2+ . Correspondingly, the luminescence changes from red to bright green and finally back to red emission. By fabricating a test‐paper containing CsMnCl 3 (H 2 O) 2 , DMAC and DMF can be detected quickly with a response time of less than one minute. These results can expand potential applications for low‐dimensional lead‐free perovskites.