Modulating Coordination Microenvironment of Metal Ions to Tune the Photochromic Performances of Three Hybrid Zincophosphites with Isotopological Architecture

The development of new hybrid photochromic materials (HPMs) systems received huge interest of chemists because of their potentialities in many domains and feasibilities of obtaining other photomodulated chemo-physical properties. The photoinduced electron transfer (ET) based on electron-donor (ED) and electron-acceptor (EA) species, together with a crystal engineering strategy, has been efficient in fabricating crystalline HPMs (CHPMs) with a tunable photoresponsive functionality. Compared with the previously investigated polypyridines as EAs, in this work, the introduction of polyimidazoles, tris(4-(1H-imidazol-1-yl)phenyl)amine (TIPA) as potential EAs, into a zinc-halogen ion (X– = Cl–, Br–, I–)-phosphite system produces three hybrid phosphites, [Zn2Cl2(HPO3)(TIPA)] (1), [Zn2Br2(HPO3)(TIPA)]·2H2O (2), and [Zn4I2(HPO3)2(HCO2)2(TIPA)2]·3H2O (3). In isostructural 1 and 2, the TIPA bridges neutral tetramers [Zn4(μ3-HPO3)2X4] to form a layered structure. Complex 3 features similar building units of [Zn4(μ3-HPO3)2I2(HCOO)2], which could be viewed as the partial substitution of terminal ligands X– of [Zn4(μ3-HPO3)2X4] with formate (HCOO–). In 3, the TIPA connects tetranuclear units to yield the resulting layered skeleton. As anticipated, 1–3 exhibit photochromism driven by the ET from tetranuclear species as EDs to TIPA as EAs. Although 1–3 have an isotopological architecture with the same linkers as EAs and similar building units as EDs, they exhibit distinct photochromic performances. Their photochromic performances could be modulated by the coordination microenvironment of metal ions of the tetranuclear units. Our work provides a facile method to tune the photochromic functionality of the resulting complexes via modulating the coordination microenvironment of metal ions or building units.