Multifunctional naphthalene diimide-based coordination polymers: Photochromism and solventchromism

Naphthalene diimides (NDIs), a class of organic dyes with high photochemical activity and high redox activity, have attracted considerable interest attributing to their photoinduced electron transfer to form stable radical anions upon irradiation in the presence of electron donors. In this study, a naphthalenediimide-based ligand and different aromatic carboxylic acids self-assembled in the presence of zinc ions, forming three novel coordination polymers, [Zn-2 (DPMNI) (TPDC)(2)] (1), [Zn (DPMNI) (BBC)] (2), Zn (DPMNI) (HBTC) (3) (DPMNI = N,N'-bis(4-pyridylmethyl)-1,4,5,8-naphthalene diimide, H2TPDC = thiophene-2,5-dicarboxylic acid, H2BPC = 4,4'-biphenyldicarboxylic acid, H3BTC = 1,3,5-benzenetricarboxylic acid). These coordination polymers characterized by single-crystal X-ray diffraction, elemental analyses, IR spectroscopy, powder X-ray diffraction, and theromgravimetric analysis. Because of the presence of electron-deficient NDI moieties, they exhibit reversible photochromic properties. Furthermore, due to the different pi-pi interactions between the NDI moieties and aromatic carboxylic acid, compounds 1-3 exhibit different photosensitive properties. Moreover, the solvatochromic behaviour of compound 1 was also investigated.