Visual Observation of Contact‐Induced Intercrystalline Migration of Aromatic Species Adsorbed in Zeolites by Fluorescence Microscopy

Abstract

Intercrystalline migration and a migration-assisted chemical reaction of adsorbed aromatic species between zeolite particles in physical contact were visualized by fluorescence microscopy coupled with a particle manipulation technique. The luminescence color characteristics of particular zeolite particles originating from the specific photochemistry of adsorbed species was exploited to follow the migration of the molecules. Two examples are shown that are relevant to the visualization of the time-dependent migration process: A one guest-two sets of zeolite crystals system: chrysene (Chry)-loaded zeolite Na+ -X (the sodium form of zeolite X) crystals were placed in contact with unloaded Tl+ -X (thallium-exchanged X) crystals and allowed to stand at room temperature. Initially, the blue fluorescence of Chry was detected only from the Na+ -X particles, but later, the development of green phosphorescence emission was discernible from the Tl+ -X which suggests that Chry migrated from the Na+ -X to the Tl+ -X crystals. A two guest-species systems: Electron-donating Chry-loaded Na+ -X crystals were placed in contact with electron-accepting 1,2,4,5-tetracyanobenzene (TCNB)-loaded Na+ -X or Na+ -Y crystals. With time, the former system (Chry/Na+ -X and TCNB/Na+ -X) gave rise to the emission of Chry-TCNB charge-transfer complexes resulting mainly from the migration of Chry while the latter system (Chry/Na+ -X and TCNB/Na+ -Y) afforded the same emission resulting largely from the migration of TCNB. The present investigation reveals that there is a certain direction for guest migration depending on the zeolite host and the nature of host-guest or guest-guest interaction.

Supramolecular photochemistry in zeolites: From catalysts to sunscreens

“…This has been observed for anthracene in zeolites NaX and NaY [16,57]. Guest exit from the particle interior has also been observed in similar systems by fluorescence microscopy [58,59] Sample aging can also be an important factor in terms of guest distribution. The emission spectra recorded immediately after preparation of pyrene encapsulated in zeolite Y indicates the presence of predominantly the excimer (excited dimer) form, despite the fact that the calculated occupancy is well below a value indicating doubly occupied cavities [55].…”

Three‐Dimensional Visualization of Defects Formed during the Synthesis of Metal–Organic Frameworks: A Fluorescence Microscopy Study

“…Like in previous studies, fluorescence microscopy reveals heterogeneity within the sample. [33][34][35] Although the vast majority of HKUST-1 crystals display the planar-type defects discussed above after extended crystallization times, some exceptions show other types of defects that are strictly confined to the crystal interior and thus hard to observe using surface imaging techniques ( Figure S2).…”

Fluorescence Microscopy: Bridging the Phase Gap in Catalysis

“…Intercrystalline diffusion between zeolite X crystals in a powder sample has been probed using chrysene or perylene as a guest and NaX or TlX zeolites as hosts [48][49][50]. In a physical mixture of chrysene-loaded NaX and unloaded TlX, one can easily determine the location of the chrysene: chrysene gives a blue fluorescence in NaX, but in TlX, a green phosphorescence is seen, because of spin-orbit interaction with Tl + cations.…”

“…These instruments can directly observe and quantify metal atoms and adatoms on surfaces. Scanning probe techniques are however typically limited to single, idealized crystals in ultrahigh-vacuum conditions (UHV), and www.elsevier.com/locate/cattod Catalysis Today 126 (2007) [44][45][46][47][48][49][50][51][52][53] the discrepancy between such conditions and industrial catalysis ('pressure gap', 'materials gap') has been debated increasingly in the past years. The 'pressure gap' refers to the difference between the UHV conditions of classical surface science (<10 À9 bar) and the pressures in industrial applications (1 to 10 3 bar).…”