Encapsulating Halometallates into 3-D Lanthanide-Viologen Frameworks: Controllable Emissions, Reversible Thermochromism, Photocurrent Responses, and Electrical Bistability Behaviors.

The encapsulation of guests into metal-organic frameworks (MOF) is an efficient strategy to generate novel multifunctional materials with enhanced properties. Herein, four halometallate@MOF composites with formulas of {(Pb2I4Br3)[(Pr(bpdo)4(H2O)2]·(H2O)}n (1), {[Pb3I10(H2O)2][Y2(bpdo)5(OH)2]·4(H2O)}n (2), {(Bi2I9)[(Pr(bpdo)3(H2O)]}n (3), {(Bi4I18)[(La(bpdo)4(H2O)2]2}n (4) (bpdo = 4,4'-bipyridine N,N'-dioxide) were prepared. In these composites, lanthanide-viologen MOF act as matrices, whose cavities were penetrated by halometallates. Consequently, the insertion of electron-rich halometallates into electron-deficient lanthanide-viologen matrices leads to the presence of strong room temperature charge transfer (CT) interactions. Importantly, these composites exhibit enhanced photo/thermal stabilities, controllable white emissions, reversible thermochromisms, and good photocurrent response performances. Specially, the memory devices based on these composites illustrate reversible electrical bistability behaviors, which can be assigned to ohmic and space-charge-limited conduction (SCLC) mechanisms. This kind of composite can be utilized as a multifunctional platform with enhanced stability.