Photophysical Properties and Electrochromism of Viologen Encapsulated Viologen@InBTB Metal–Organic Framework

Abstract

The encapsulation of various types of guest molecules into the preorganized channels of metal–organic frameworks (MOFs) is continuously motivating chemists searching for better MOF host materials to systematically alter or control the photophysical properties of the captured guests in a controlled manner. The unique spatial distribution and a certain preferential geometry of the guests inside MOFs often render guests to exhibit distinct optical properties. Three different viologen cations were encapsulated into the mesoscale channels of negatively charged InBTB MOF ([Et2NH2]3[In3(BTB)4]·10DEF·14H2O, H3BTB = 1,3,5‐benzenetribenzoic acid) via cation exchange process. The cationic viologens were partially encapsulated through cation exchange with [Et2NH2]+ counter‐cations to afford viologen@InBTB. The colorless InBTB crystals changed into yellow in the case of viologen@InBTB. The fluorescence measurement of methylviologen (MV2+) encapsulated MV@InBTB showed different behavior compared to ethylviologen (EV2+) and benzylviologen (BV2+) encapsulated InBTB. Both EV@InBTB and BV@InBTB exhibited unusual quenching of the photoluminescence emission in solid state.