Two host-guest 2D MOFs based on hexyl viologen cations: Photochromism

Abstract

Two host-guest two-dimensional (2D) MOFs based on N,N′-bis(n-hexyl)-4,4′-bipyridinium dibromide (HVBr2) were prepared {(HV)0.5(C2H8N)[Zn3O(m-BDC)3(H2O)2]·DMF}n (1), {(HV)[Cd3(m-BDC)4(H2O)2]·DMF·4H2O}n (2) (m-H2BDC = 1,3-benzenedicarboxylic acid), which were investigated on the basis of crystal structures, chromic properties, and molecular orbitals. Each metal ion connects m-BDC2− ligands to form a 2D anionic framework, which is constructed in a grid-like square cavities with the intersections of HV2+ cations to achieve charge balance. MOFs 1 and 2 each exhibit photochromic properties. The B3LYP/6–311 (d,p) method of density functional theory (DFT) was applied to explore electronic structures and matching rules between donors and receptors. The results indicate that the balance between electron transfer and photochromic properties is achieved by the regulation of receptors and donors.