Thermal treatment of Ag(+)-exchanged zeolites yields discrete highly photostable luminescent clusters without formation of metallic nanoparticles. Different types of emitters with characteristic luminescence colors are observed, depending on the nature of the cocation, the amount of exchanged silver, and the host topology. The dominant emission bands in LTA samples are situated around 550 and 690 nm for the samples with, respectively, low and high silver content, while in FAU-type materials only a broad band around 550 nm is observed, regardless of the degree of exchange. Analysis of the fluorescent properties in combination with ESR spectroscopy suggests that a Ag(6)(+) cluster with doublet electronic ground state is associated with the appearance of the 690-nm emitter, having a decay of a few hundred microseconds. Tentatively, the nanosecond-decaying 550-nm emitter is assigned to the Ag(3)(+) cluster. This new class of photostable luminescent particles with tunable emission colors offers interesting perspectives for various applications such as biocompatible labels for intracellular imaging.

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Understanding the internal structure of ZSM-5 crystallites is essential for improving catalyst performance. In this work, a combination of fluorescence microscopy, AFM, SEM, and optical observations is employed to study intergrowth phenomena and pore accessibility in a set of five ZSM-5 samples with different crystal morphologies. An amine-functionalized perylene dye is used to probe acid sites on the external crystal surface, while DAMPI (4-(4-diethylaminostyryl)- N-methylpyridinium iodide) is used to map access to the straight channels in MFI from the outer surface. The use of these dyes is validated by studying the well-understood rounded-boat type ZSM-5 crystals. Next coffin-shaped ZSM-5 crystals are considered; we critically evaluate the seemingly conflicting 2-component and 3-component models that have been proposed to account for the hourglass structure in these crystals. The data prove that observation of an hourglass structure is essentially unrelated to a 90 degree rotation of the pyramidal crystal components under the (010) face. Hence, in perfectly formed coffin-shaped crystals, the straight channels can be accessed from (010). However, in other crystal batches, sections with a 90 degrees rotation can be found; they are indeed located inside the crystal sections under (010) but often only partially occupy these pyramidal components. In such a case, both straight and sinusoidal pores surface at the hexagonal face. The results largely support the 3-component model, but with the added notion that 90 degree rotated sections (as proposed in the 2-component model) are most likely to be formed inside the defect-rich, pyramidal crystal sections under the (010) faces.

Structural and temporal inhomogeneities can have a marked influence on the performance of inorganic and biocatalytic systems alike. While these subtle variations are hardly ever accessible through bulk or ensemble averaged activity screening, insights into the molecular mechanisms underlying these diverse phenomena are absolutely critical for the development of optimized or novel catalytic systems and processes. Fortunately, state-of-the-art fluorescence microscopy methods have allowed experimental access to this intriguing world at the nanoscale. In this tutorial review we will first provide a broad overview of key concepts and developments in the application of single molecule fluorescence spectroscopy to (bio)catalysis research. In the second part topics specific to both bio and heterogeneous catalysis will be reviewed in more detail.

The ever-improving time and space resolution and molecular detection sensitivity of fluorescence microscopy offer unique opportunities to deepen our insights into the function of chemical and biological catalysts. Because single-molecule microscopy allows for counting the turnover events one by one, one can map the distribution of the catalytic activities of different sites in solid heterogeneous catalysts, or one can study time-dependent activity fluctuations of individual sites in enzymes or chemical catalysts. By experimentally monitoring individuals rather than populations, the origin of complex behavior, e.g., in kinetics or in deactivation processes, can be successfully elucidated. Recent progress of temporal and spatial resolution in single-molecule fluorescence microscopy is discussed in light of its impact on catalytic assays. Key concepts are illustrated regarding the use of fluorescent reporters in catalytic reactions. Future challenges comprising the integration of other techniques, such as diffraction, scanning probe, or vibrational methods in single-molecule fluorescence spectroscopy are suggested.S ingle-molecule fluorescence spectroscopy (SMFS) has recently developed into a powerful tool for studying biophysical and biochemical phenomena. In studies of enzymatic catalysis, SMFS has revealed that there are large differences between the catalytic activity of individual enzymes within a population (''static disorder'') and that the rate constant (k cat ) of an individual enzyme may strongly fluctuate over time (''dynamic disorder''), the latter resulting from conformational changes of the enzyme. The recent application of SMFS to catalysis by solid materials has shown that heterogeneities in k cat also exist between individual catalytic crystals of one powder sample and even between the sites of an individual crystal. In this case, heterogeneity might arise from different chemical environments within the catalyst sample. The observation of heterogeneity in the k cat of those different catalytic systems suggests that the parallel introduction and evolution of SMFS techniques in bioand chemocatalysis will deepen our insights in almost any type of catalytic conversion. Indeed, the challenge to derive overall kinetics from the contributions of individuals within a population is essentially the same for biological, heterogeneous and even homogeneous systems, as discussed in From Populations to Individuals.From a technical viewpoint, SMFS requires strongly fluorescent probe molecules. The concepts to use such probes and even the probes themselves can be exchanged freely between heterogeneous, homogeneous, and biocatalysis, as discussed in Probes for SMFS in (Bio)Catalysis. If one wants to map in even more detail the contributions of the individual enzymes or catalytic sites to the overall kinetics, further improvements of the spatial and temporal resolution of SMFS will be required (see Spatial Resolution: Micro-and Nanoscopy and Time Resolution and Dynamics). Finally, to complement the information from S...