Adsorption of a water-soluble molecular rotor fluorescent probe on hydrophobic surfaces.

Environmentally sensitive molecular rotors are widely used to probe the local molecular environment in e.g. polymer solutions, polymer glasses, and biological systems. These applications make it important to understand its fluorescence properties in the vicinity of a solid surface, since fluorescence microscopy generically employs cover slides, and measurements are often done in its immediate vicinity. Here, we use a confocal microscope to investigate the fluorescence of (4-DASPI) in glycerol/water solutions close to the interface using hydrophilic or hydrophobic cover slips. Despite the dye's high solubility in water, the observed lengthening of the fluorescence lifetime close to the hydrophobic surface, implies a surprising affinity of the dye with the surface. Because the homogeneous solution and the refractive index mismatch reduces the optical sectioning power of the microscope, we quantify the affinity with the help of a simple model of the signal vs. depth of focus, exhibiting surface and bulk contributions. The model reduces artefacts due to refractive index mismatch, as supported by Monte Carlo ray tracing simulations.

Novel Hydroquinone-Alumina Composites Stabilizing a Guest-Free Clathrate Structure: Applications in Gas Processing.

Organic clathrates formed by hydroquinone (HQ) and gases such as CO2 and CH4 are solid supramolecular host-guest compounds in which the gaseous guest molecules are encaged in a host framework of HQ molecules. Not only are these inclusion compounds fascinating scientific curiosities but they can also be used in practical applications such as gas separation. However, the development and future use of clathrate-based processes will largely depend on the effectiveness of the reactive materials used. These materials should enable fast and selective enclathration and have a large gas storage capacity. This article discusses the properties and performance of a new composite material able to form gas clathrates with hydroquinone (HQ) deposited on alumina particles. Apart from the general characterization of the HQ-alumina composite, one of the most remarkable observations is the unexpected formation of a guest-free clathrate structure with long-term stability (>2 years) inside the composite. Interestingly enough, in addition to a slight improvement in the enclathration kinetics of pure CO2 compared to powdered HQ, preferential capture of CO2 molecules is observed when the HQ-alumina composite is exposed to an equimolar CO2/CH4 gas mixture. In terms of gas capture selectivity toward CO2, the performance of this new composite exceeds that of pure HQ and HQ-silica composites developed in a previous study, opening up new opportunities for the design and use of these novel materials for gas separation.