Unprecedented second-timescale blue/green emissions and iodine-uptake-induced single-crystal-to-single-crystal transformation in Zn(II)/Cd(II) metal-organic frameworks

Abstract

The long-persistent phosphorescent metal-organic framework (MOF) is a kind of highly desirable but rare material. Here, two new molecular MOF materials, {[Zn(tipa)Cl]⋅NO3⋅2 DMF}n (1) and {[Cd2(tipa)2Cl4]⋅6 DMF}n (2) (tipa = tri(4-imidazolylphenyl)amine), which have 3D twofold interpenetrated (utp) and 2D noninterpenetrated (kgd) topologies, respectively, are reported. They exhibit unexpected long-persistent emissions yet reported: At 77 K, they persist in glowing after stopping the UV irradiation on a timescale up to seconds at 77 K, which can be detected by the naked eye (ca. 2 s). Compounds 1 and 2 also undergo single-crystal-to-single-crystal (SC-SC) transformations through different routes; a simple anion-exchange route for 1 and a complicated replacement of μ1-Cl(-) ions by DMF molecules accompanying I3(-) captured in the void for 2.

Keywords: X-ray diffraction; cadmium; iodine; metal-organic frameworks; phosphorescence; zinc.