By incorporating electroactive triphenylamine units into a hexacarboxylate linker, two zinc-based metal-organic frameworks with 3,24-connected rht net were constructed, demonstrating unique anion-dependent intermolecular charge/electron and energy transfer. The crystals of Zn-MOF-1 incorporating nitrate anions within the framework are red and do not show fluorescence at all, while Zn-MOF-2 containing fluoroborate anions within the framework is colorless and exhibits significant fluorescence. Cyclic voltammetry further revealed that the two anions present in the frameworks exerted different influence on the electron transfer processes between the triphenylamine units within the framework. Furthermore, fluorescence quenching experiments with electron-deficient nitrobenzene on Zn-MOF-2 were conducted, indicating favorable electron transfer between the electron-rich linkers and electron-deficient guests. A highly luminescent energy transfer composite (DMASM@Zn-MOF-2) was achieved, which exhibited excellent dual-emission performance and adjustable dual-emission intensity accompanied by a variable emission color observed with the naked eye. In all, the two rare rht-type Zn-MOFs incorporating different anions within respective frameworks were constructed for the first time and can serve as a unique platform to uncover previously rarely explored charge/electron and energy transfer interactions related to the nature of anions, thereby enabling the rational design and construction of multifunctional MOF materials.
Ma et al. (Fri,) studied this question.