Electrocatalytic Energy Release of Norbornadiene-Based Molecular Solar Thermal Systems: Tuning the Electrochemical Stability by Molecular Design.

Molecular solar thermal (MOST) systems, such as the norbornadiene/quadricyclane (NBD/QC) couple, combine solar energy conversion, storage, and release in a simple one-photon one-molecule process. Triggering the energy release electrochemically enables high control of the process, high selectivity, and reversibility. In this work, the influence of the molecular design of the MOST couple on the electrochemically triggered back-conversion reaction was addressed for the first time. The MOST systems phenyl-ethyl ester-NBD/QC (NBD1/QC1) and p-methoxyphenyl-ethyl ester-NBD/QC (NBD2/QC2) were investigated by in-situ photoelectrochemical infrared spectroscopy, voltammetry, and density functional theory modelling. For QC1, partial decomposition (40 %) was observed upon back-conversion and along with a voltammetric peak at 0.6 Vfc , which was assigned primarily to decomposition. The back-conversion of QC2, however, occurred without detectable side products, and the corresponding peak at 0.45 Vfc was weaker by a factor of 10. It was concluded that the electrochemical stability of a NBD/QC couple is easy tunable by simple structural changes. Furthermore, the charge input and, therefore, the current for the electrochemically triggered energy release is very low, which ensures a high overall efficiency of the MOST system.

Molecular Solar Thermal Batteries through Combination of Magnetic Nanoparticle Catalysts and Tailored Norbornadiene Photoswitches.

Cobalt catalysts are immobilized on the surface of iron oxide nanoparticles for the preparation of highly active quasi-homogeneous catalysts toward an efficient release of photochemically stored energy in norbornadiene-based photoswitches. The facile separation of the iron oxide nanoparticles through exploitation of the intrinsic magnetic properties of this material enables efficient cyclization of energy storage and release. Through the transition from cobalt (II) salphen to cobalt porphyrins, a 22.6-fold increase in the catalytic efficiency of the QC-NBD back-conversion is achieved, with an initial TOF of up to 3.64 s-1 and excellent TON of over 3305. In addition, a series of novel "push-pull" functionalized norbornadiene derivatives is prepared, featuring excellent absorption properties with maxima up to 366 nm, quantum yields around 70 %, high energy storage capacities of up to 98.0 kJ mol-1 , and outstanding thermal stability with t1/2 (25 °C) over 100 days. Finally, the energy storage potential of these molecular solar thermal (MOST) systems is harnessed in a heat release experiment. This demonstrates the potential of norbornadiene-based photoswitches in combination with efficient magnetic catalysts for the generation of environmentally benign process heat.

Non-Covalent Postfunctionalization of Dye Layers on TiO2 - A Tool for Enhancing Injection in Dye-Sensitized Solar Cells.

We report on newly tailored dye layers, which were employed, on one hand, for covalent deposition and, on the other hand, for non-covalently post-functionalizing TiO2 nanoparticle films. Our functionalization concept enabled intermixing a stable covalent attachment of a first layer with a highly versatile and reversible hydrogen bonding through the Hamilton receptor-cyanuric acid binding motif as a second layer. Following this concept, we integrated step-by-step a first porphyrin layer and a second porphyrin/BODIPY layer. The individual building blocks and their corresponding combinations were probed with regard to their photophysical properties, and the most promising combinations were implemented in dye-sensitized solar cells (DSSCs). Relative to the first porphyrin layer adding the second porphyrin/BODIPY layers increased the overall DSSC efficiency by up to 43 %.

Encapsulation of Hydrophobic Drugs in Shell-by-Shell Coated Nanoparticles for Radio-and Chemotherapy-An In Vitro Study.

Our research objective was to develop novel drug delivery vehicles consisting of TiO2 and Al2O3 nanoparticles encapsulated by a bilayer shell that allows the reversible embedment of hydrophobic drugs. The first shell is formed by covalent binding of hydrophobic phosphonic acid at the metal oxide surface. The second shell composed of amphiphilic sodium dodecylbenzenesulfonate emerges by self-aggregation driven by hydrophobic interactions between the dodecylbenzene moiety and the hydrophobic first shell. The resulting double layer provides hydrophobic pockets suited for the intake of hydrophobic drugs. The nanoparticles were loaded with the anticancer drugs quercetin and 7-amino-4-methylcoumarin. Irradiation with X-rays was observed to release the potential anticancer drugs into the cytoplasm. In Michigan Cancer Foundation (MCF)-10 A cells, quercetin and 7-amino-4-methylcoumarin acted as antioxidants by protecting the non-tumorigenic cells from harmful radiation effects. In contrast, these agents increased the reactive oxygen species (ROS) formation in cancerous MCF-7 cells. Quercetin and 7-amino-4-methylcoumarin were shown to induce apoptosis via the mitochondrial pathway in cancer cells by determining an increase in TUNEL-positive cells and a decrease in mitochondrial membrane potential after irradiation. After X-ray irradiation, the survival fraction of MCF-7 cells with drug-loaded nanoparticles considerably decreased, which demonstrates the excellent performance of the double-layer stabilized nanoparticles as drug delivery vehicles.

Shell-by-Shell Functionalization of Inorganic Nanoparticles.

The current state of the hierarchical chemical functionalization of inorganic nanoparticles (NPs) by shell-by-shell (SbS)-assembly of organic layers around the NP cores is summarized. This supramolecular functionalization concept is based on two steps: 1) the covalent grafting of a first ligand-shell consisting of, for example, long chain phosphonic acids and 2) the noncovalent interdigitation of amphiphiles forming the second ligand shell. The latter process is guaranteed predominantly by solvophobic interactions. These highly order organic-inorganic hybrid architectures are currently an emerging field at the interface of synthetic chemistry, nanotechnology, and materials science. The doubly functionalized NPs display tunable materials properties, such a controlled dispersibility and stability in various solvents, highly efficient trapping of guest molecules in between the ligand shells (water cleaning) as well as compartmentalization and modification of electronic interactions between photoactive components integrated in such complex nano-architectures. Such SbS-functionalized NPs have a high potential as water-cleaning materials and also some first prototype applications as biomedicinal therapeutics have been presented.

Highly Efficient Encapsulation and Phase Separation of Apolar Molecules by Magnetic Shell-by-Shell-Coated Nanocarriers in Water.

We report on the development of a supramolecular nanocarrier concept that allows for the encapsulation and separation of small apolar molecules from water. The nanocarriers consist of shell-by-shell-coated nanoparticles such as TiO2 and ferromagnetic Fe3 O4 . The first ligand shell is provided by covalently bound hexadecyl phosphonic acid (PAC16 ) and the second shell by noncovalently assembled amphiphiles rendering the hybrid architecture soluble in water. Agitation of these constructs with water containing the hydrocarbons G1-G4, the fluorescent marker G5, the polychlorinated biphenyl PCB 77, or crude oil leads to a very efficient uptake (up to 411 %) of the apolar contaminant. In case of the hybrids containing a Fe3 O4 core, straightforward phase separation by the action of an external magnet is provided. The load can easily be released by a final treatment with an organic solvent.