On the Reversible Photoisomerization of Spiropyran‐Modified Zeolite L Single Crystals

Abstract

Photoisomerization of spiropyrans has been the subject of many interesting studies in a wide number of fields, such as sensors for cations, [1] sensors of pH, [2] switchable surfaces, [3] lasing effect, [4] among many others. This molecule can be photoisomerized upon UV irradiation, giving rise to the zwitterionic merocyanine (MC) form, which dramatically changes its hydrophilicity and photophysical properties (see Scheme 1). Irradiation in the visible region or heating brings back the spiropyran (SP) to the MC form. Solvent polarity and pH have been already shown to strongly influence the properties of spiropyrans.[5] SP does not absorb in the visible range, while the merocyanine, which absorbs at ca 570 nm (in DMSO), exhibits red fluorescence and its lifetime is typically about 260 ps. [6] Recently the use of spiropyrans in the field of dual emission for bio-imaging has been reported, where silica nanoparticles containing spiropyran and a green-emitting perylene derivative were shown to exhibit green or red emission depending on the UV/Vis irradiation. [7] Such systems may become even more efficient if the dyes embedded inside the porous silica nanoparticles aggregate as little as possible, as well as if the dyes are completely isolated from the biosystem being labeled. This problem may be addressed by combining spiropyrans with versatile porous materials, such as zeolite L, which are known to encapsulate organic dyes in the monomeric form and to protect them against the outer chemical environment.Zeolite L is a porous aluminosilicate material consisting of thousands of one-dimensional nanochannels parallel to each other, which run throughout the long axis of the crystal.[8] Zeolite L can be used not only as luminescent devices, [9] in bioimaging, [10] or in photodynamic treatments, [11] but also in many other applications.[12] This class of crystals can still be functionalized on glass, indium-tin oxide or other substrates and can be synthesized from 50 nm up to 20 mm, [13] which may be strategic, depending on the application. SP-functionalized zeolite L crystals with encapsulated dyes may be an interesting option to make new dual emitters, which can be used in bio-imaging experiments, even without taking advantage of energy transfer between encapsulated dyes and SP. Because cells may exhibit auto-fluorescence, a system having two different emissions at different times allows for distinguishing between the auto-fluorescence and the luminescence of the dual-emitters, simply by direct visualization of the sample in the microscope.The advantages of using zeolite L intead of, for example, silica nanoparticles, are: 1) the size of the zeolite L crystals can be synthetically tuned from 50 nm to 20 mm, in order to be used in different experiments; 2) the luminescence of the encapsulated dyes, which can be highly anisotropic, is also strong because the inserted dyes are in the monomeric form and are completely isolated from the outer bio-environment; 3) zeolite L has been already shown to be easily functionalized...

Supramolecular Organization in Confined Nanospaces

“…[615,666,667] The specific modification of the channel openings via the grafting of alkoxysilane moieties (Figure 42) is also fundamental to attain macroscopic organization of zeolite crystals (by covalent attachment to a support, for example) [564,670,671] and to add further functionalities. Typically, the added groups carry magnetic, [672,673] or photo/electroresponsive properties -like phthalocyanine dyes, [40,[674][675][676] spiroxanes, [677] Ru 2 + [562] and Ir(III) [678] complexes. Stopcocks can also be used for molecular recognition processes: for instance, the end-modification of zeolite L with adamantane allowed for the selective aggregation of b-cyclodextrin-coated gold nanoparticles at the zeolite crystal terminations.…”

Cyclodextrin‐Modified Zeolites: Host–Guest Surface Chemistry for the Construction of Multifunctional Nanocontainers

“…Owing to the presence of Al, the framework is negatively charged, which endows the zeolites with cation‐exchange capabilities, thus allowing the uptake and release of charged molecules 9. Some studies concern the surface modification of zeolite L for the attachment of Gd III ‐ and Eu III ‐DOTA (1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid) complexes for MRI imaging,10 an arginylglycylaspartic (RGD) peptide for cell adhesion,11 or spiropyran for biosensing 12. However, to address the suitability of zeolite L as a potential drug carrier, functionalization of its outer surface needs to be studied congruently with its uptake and release properties as the former may influence the latter.…”

“…[9] Some studies concern the surface modification of zeolite L for the attachment of Gd III -and Eu III -DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) complexes for MRI imaging, [10] an arginylglycylaspartic (RGD) peptide for cell adhesion, [11] or spiropyran for biosensing. [12] However, to Abstract: The functionalization of nanoporous zeolite L crystals with bcyclodextrin (CD) has been demonstrated. The zeolite surface was first modified with amino groups by using two different aminoalkoxysilanes.…”

Designing Dye–Nanochannel Antenna Hybrid Materials for Light Harvesting, Transport and Trapping

“…The third stage of organization is obtained by interfacing the material to an external device via a stopcock intermediate; see Figure 8. [10,15,42,47,48,[71][72] A possibility to achieve higher levels of organization is by controlled assembly of zeolite crystals into oriented structures and preparation of monodirectional materials, as we have discussed. The usually strong light scattering of ZL can be suppressed by refractive index matching and avoidance of microphase separation in hybrid polymer/dye-ZL materials.…”