Five monocyclic pyridinium derivative based halo-argentate/cuprate hybrids or iodide salts: influence of composition on photochromic behaviors

The rational choice of an electron acceptor was proved to be an effective strategy for the development of novel electron transfer (ET) photochromic iodides, but the types and amounts of reported electron acceptors are relatively limited so far, especially for monocyclic aromatic molecules. Herein, using monocyclic pyridinium derivatives (N-protonation-4-carboxypyridinium/N-protonation-4-carbamoylpyridinium/1-methyl-4-(carbomethoxy)pyridinium) as structural directing agents and electron acceptors, five new electron donor-acceptor-based halo-argentate/cuprate hybrids or iodide salts have been synthesized, including [HINA][Ag4I5] (1), [HINAM]I (2), [HINAM]I·0.5(I2) (3), [MCMP][Ag2Br3] (4) and [MCMP][Cu2I3] (5). Noteworthily, compounds 1-3 exhibit interesting photochromic behaviours, while compounds 4 and 5 are non-photochromic. Finally, the possible chromic mechanisms and influencing factors for the title compounds were also discussed.