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A micro-spectroscopic method has been developed to probe the accessibility of zeolite crystals using a series of fluorescent 4-(4-diethylaminostyryl)-1-methylpyridinium iodide (DAMPI) probes of increasing molecular size. Staining large zeolite crystals with MFI (ZSM-5) topology and subsequent mapping of the resulting fluorescence using confocal fluorescence microscopy reveal differences in structural integrity: the 90° intergrowth sections of MFI crystals are prone to develop structural imperfections, which act as entrance routes for the probes into the zeolite crystal. Polarization-dependent measurements provide evidence for the probe molecule's alignment within the MFI zeolite pore system. The developed method was extended to BEA (Beta) crystals, showing that the previously observed hourglass pattern is a general feature of BEA crystals with this morphology. Furthermore, the probes can accurately identify at which crystal faces of BEA straight or sinusoidal pores open to the surface. The results show this method can spatially resolve the architecture-dependent internal pore structure of microporous materials, which is difficult to assess using other characterization techniques such as X-ray diffraction. [ABSTRACT FROM AUTHOR]

This road is limited to molecules with a width of 6 Å or less! One of the goals of microscopy is to enlarge our view of functional materials in such a way that we can see what is really going on, as if it were an everyday object you can hold in your hand or walk around. The cover depicts a zeolite scientist's utopia: using model zeolite crystals so large that you can walk around inside. In this work, we learn more about the accessibility of zeolite materials by using fluorescence microscopy in combination with molecules differing in their size. More information can be found in the Full Paper by B. M. Weckhuysen, et al. on page 6305 ff. [ABSTRACT FROM AUTHOR]