The low formation energy of metal halide perovskites (MHPs) and their high performance in optoelectronic applications make them rather interesting semiconductor materials. In this work, we take advantage of the tunability of two-dimensional (2D) halide perovskites of the type A2PbI4 to explore a chromogenic mechanism in these materials where methylamine is allowed to intercalate into and deintercalate from the halide perovskite films. Methylamine intercalation results in a change in color from the initial yellow/orange color of the A2PbI4 films to visibly transparent films, while deintercalation leads to a return of a colored film. The reversibility of this solvatochromic mechanism was found to be highly dependent on the nature of the A-site cation used. We observe the formation of iodoplumbate phases, mixed 2D/three-dimensional (3D) perovskites, and/or 3D perovskites as secondary phases formed in some systems and, by exploring a wide array of A2PbI4 materials, we identify key design rules for the A-site cation to limit secondary phase formation and structural changes associated with methylamine intercalation/deintercalation. Specifically, the effects of changing cation–cation, cation “head”-inorganic, and cation “tail”-inorganic interactions in this system are demonstrated. By carefully controlling these interactions, more robust solvatochromic systems are realized. These initial explorations of metal halide solvatochromism improve the understanding of A-site cation design in A2PbI4 MHPs and show that these are a promising class of solvatochromic semiconductors.

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