Thionine Dye Confined in Zeolite L: Synthesis Location and Optical Properties

Abstract

The process of light conversion is at present deeply investigated to develop more efficient devices for artificial photosynthesis, water splitting, photovoltaic applications, and targeting therapeutic agents. This process is induced by nanostructured functional materials, such as zeolites light sensitized by dye molecules adsorbed into their pores. Here a detailed study of the organization of the cationic dye thionine (Th) inserted into the linear 12MR channels of zeolite L is carried out by XRPD, FT-IR spectroscopyfor the determination of the host−guest interactionsand UV−vis absorption and photoluminescence spectroscopies for the investigation of the electronic states of the guest. Two composites with different Th loading (labeled ZL/0.15Th and ZL/0.27Th) were obtained through ion exchange. TGA spectra and IR-ATR spectroscopy clearly indicated penetration of Th molecules into the ZL channels. Rietveld structural refinement showed that Th molecules in both composites are aligned parallel to the 12MR channel axis and located on the mirror planes parallel to the c-axis. Water molecules interact strongly with the dye and form a kind of solvent−matrix tube shaped around the Th molecule, favoring the upright arrangement of the molecules. DR−UV−vis spectra of the ZL/Th composites indicated that Th molecules are hosted in the ZL channels in a monomeric form. Photoluminescence spectroscopy demonstrated that photoluminescent dyes correspond to ca. 5% of the total amount of Th molecules in the zeolite porosities. While most of the photoluminescent Th molecules exhibit a lifetime equivalent to Th in solutions, the complementary fraction of photoluminescent Th exhibit significantly longer lifetimes, resulting from an entrapment in defects of the zeolite structure, inducing strong rotational constraints to the molecules.

Supramolecular Organization in Confined Nanospaces

“…Nonetheless, the atomistic structure of these versatile compounds often remains unexplored, as suggested by the scarce number of diffraction studies on dye‐zeolite hybrids ,. Fortunately, computational modeling comes to the rescue .…”

Compressibility behavior and pressure-induced over-hydration of zeolite K AlSi-L

“…The packing of the molecules inside the channel can be modified by increasing the molecules loading, or, for example, applying pressure. Notwithstanding, several studies have dealt with the incorporation of dyes into zeolites [10][11][12][13][14][15], only a work [16] until now exploited the behavior of these systems under high pressure trying to establish whether compression could favor a different distribution of the dye molecules and lead to an improvement of the optical properties of the materials under investigation. Very recently, Gigli et al [16] studied the high-pressure behavior of some hybrid composites formed by zeolite L and fluorenone dye, through an integrated experimental-computational approach.…”

The spatial distribution of the photostability of thionine in zeolite L nanochannels investigated by Photobleaching Lifetime Imaging Microscopy

“…Owing to the molecular dimension of this dye (0.72 x 1.5 nm) and space restrictions imposed by the geometry of ZL, thionine exists within the channels exclusively as a monomer. 13 In this report, wide field fluorescence microscopy is used to generate photobleaching lifetime images of thionine encapsulated in ZL, allowing the visualization of its spatial distribution of photostability. The influence of the sample atmosphere (air and argon) and excitation irradiance on photostability patterns are also investigated.…”