Surface interaction and dynamics of molecular spin-probes as guests in tailor-made organosilica, porous hosts for applications in chromatography.

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Mass transport in, trough and out of porous solids is a deciding factor in a number of applications in process engineering, e.g. chromatography. One has to consider a hierarchical process, spanning several orders of length- and time-scales. At the molecular scale, in the range of few nanometers and picoseconds, there is a complex interplay between guest-solvent and guest-surface interactions, and this determines directly the mobility of those guests inside the porous materials. A comprehensive and scale-spanning, experimentally underpinned understanding of the transport of dissolved molecular species inside (functionalized) porous matrices is pivotal for realizing porous solids designated for particular applications (e.g. chromatography) by design rather than by empiricism. However, it is very difficult to "spot" the confined guests with sufficient temporal and spatial resolution at technically relevant conditions (in the presence of solvents and at T >= r.t.). We have successfully established electron spin resonance (ESR) spectroscopy as an analytical "eye". Now, we will advance the ESR methodology, aiming at more precise and first and foremost scale-spanning insights into the diffusion of molecular spin probes in pores. Furthermore, we are going to establish a direct link between the synthesis of tailor-made, porous materials, which will enable to exert a much more controlled influence on the mass transport of dissolved species. We will dedicate ourselves to the exciting question of effects of spectator groups, which are present in addition to the active components (predominantly taking part in the guest-surface interaction). We expect that the mobility of guest molecules is mainly dependent on the surface density of the active components, but spectator groups may have a significant importance as well due to the local affect on solvent properties, for instance. The required, systematic variations of surface properties will be realized via bifunctional organosilica materials. Due to the high degree of novelty, we anticipate a substantial acquisition of new knowledge from the combination of materials with chemical gradients and imaging ESR spectroscopy. The imaging methodology allows recording the spectroscopic signature of the guests at every position of the porous material. From these data we can obtain information about the local dynamics and mobility, and at the same time one can analyse the mass transport through the porous medium at macroscopic dimensions. The direct correlation between molecular and macroscopic transport will finally enable to investigate the separation of a compound mixture, by means of spectroscopy using two different spin probes and also for the concrete application, a chromatographic measurement.