Photophysical properties of cationic dyes captured in the mesoscale channels of micron-sized metal-organic framework crystals

Abstract

The optical properties of dye molecules in confined spaces can differ from the solution phase due to confinement effects. Pre-organized mesoscale channels of metal-organic frameworks (MOFs) are very suited for hosting various dyes, and the robust frameworks often render the encapsulated dyes with certain preferential geometries, which are different from those found in solution. Furthermore, pre-organized open channels can efficiently guide the uniform and unique spatial distribution of dye molecules in a controlled manner, which are otherwise difficult to achieve. Thus, sufficiently large dye molecules can avoid the formation of complex aggregates when captured inside open channels. In contrast, small dye molecules can form well-defined dimers or aggregates. The resulting dye-encapsulated MOFs can display unusual photophysical properties of the captured dyes. An anionic framework of In-BTB with mesoscale 3D channels is utilized for the efficient encapsulation of various cationic dyes through cation-exchange processes. Six different cationic dyes are encapsulated in the anionic framework of In-BTB, and their crystal structures are completely solved. Novel photophysical properties of these spatially distributed dye molecules in dye@In-BTBs are investigated.

Amine-Functionalized Mesoporous Silica as a Support for on-Demand Release of Copper in the A3-Coupling Reaction: Ultralow Concentration Catalysis and Confinement Effect

“…Although solid literature exists on the confinement effect for zeolites, knowledge of such phenomenon in materials with larger pores is still being built . The Kim group, for example, has shown that dyes confined in the mesopores of MOFs have photophysical properties that differ significantly from the nonconfined molecules . Another interesting work was published by the Goswami group, in which the authors were able to conduct polyol metal nanoparticles synthesis inside the pores of polystyrene and silica gel particles .…”

Catalytic oxygen evolution from hydrogen peroxide bytrans-[Co(en)2Cl2]@InBTB metal–organic framework catalytic system

“…We also observed similar phenomenon when we used EtOH for encapsulation of various cationic dyes. 6 Nonetheless, we believe that the metal–ligand connectivity may not be seriously damaged because trans -[Co(en) 2 Cl 2 ] + ions did not leach out during catalytic reactions.…”

“… 5 Several cationic dyes were also effectively incorporated into InBTB to give a series of dye@InBTB MOFs with good optical properties. 6 These examples clearly suggest that the cation-exchange-driven generation of functional MOFs is a promising strategy to develop new MOF systems with diverse functions.…”

Coexistence of 1 : 1 and 2 : 1 inclusion complexes of indigo carmine

“…Confining dye molecules in spaces not much larger than the molecules themselves 1 can drastically affect their optical properties. Both absorption and emission of dyes can be altered by encapsulation within the cavities of molecular cages, 2 metal–organic frameworks, 3,4 and protein molecules. 5 For example, cucurbit[8]uril (CB[8]) was shown to stabilize the monomeric form of perylene dyes, thus preventing undesired aggregation and enabling strong fluorescence in aqueous media.…”